AST 104 Prof B

What type of astronomical object is the sun? A star The source of the sun's energy is: nuclear fusion Light can travel through the: radiative zone The granules seen in the photosphere are the tops of convection cells in the: Convective zone Sunspots are dark spots in the: photosphere Spicules are located in the: chromosphere The solar wind is also known as the: corona The first reaction of the proton-proton chain consist of: two protons fuse to form a deuterium, releasing a neutrino, and a positron which annihilates with a nearby electron The second reaction of the proton-proton chain consist of: a deuterium and a proton fuse to form a helium-3, releasing energy in the form of gamma rays The third reaction of the proton-proton chain consists of: two helium-3 fuse to form a helium-4 plus 2 protons The solar neutrino problem has been solved. TRUE The Maunder Minimum period when sunspot activity decreased dramatically: coincided with a decrease in earth's temperature Sunspots are areas of: intense magnetic fields Over geologic time, the sun is getting: brighter

Quiz 14

1.) The most accurate method to determine the distance to nearby stars is based on the apparent shift of the star against the backgroud of more distant stars as the earth orbits the sun. This Method is called: Stellar parallax 2.) Variable stars fluctuate in: brightness 3.) Compared to a supergiant. a white dwart will have: thicker spectral lines 4.) In order to calculate a star's absolute magnitude, I need to know its: apparent magnitude and distance 5.) The reason we paid so much attention to binary stars is that by studying them, we can determines a stars: mass 6.) Most stars are solitary, as apposed to being in multiple-star systems. FALSE 7.) The computer who initially classified stars in alphabetical order according to the strength of the hydrogen line, believing she was measuring the amount of hydrogen was: Williamina Fleming 8.)The computer who arranged the spectral classification into OBAFGKM was: Annie Jump Cannon 9.) A star has a spectral classification of BOV. According to this diagram, it is: ??????????/////// 10.) According to this diagram, which star is hotter?/////// 11.) Which star is hotter? Spectral type B 12.) According to this diagram, which star is brighter?////// 13.) A star has a parallax shift of 0.05 arcseconds. How far away is it? 20 parsecs 14.) Using the average brightness of delta Cepheids in the Small Magellanic Cloud, Henrietta Leavitt was able to measure that galaxy's: distance 15.) Which type of star clusters have more stars? Globular clusters

Quiz 15 (incomplete)

1.) The gas in the interstellar medium is mostly: hydrogen and helium 2.) Bipolar jets and accretion disks are associated with: protostars 3.) Cocoon nebulae are evidence for: protostars 4.) The type of interstellar cloud which form stars are known as: molecular clouds 5.) 21-cm radio emission provides us with a means to detect: interstellar gas 6.) when hydrogen fusion stops in the core of a MS star, the core: becomes smaller and hotter 7.) A pulsar is a: neutron star 8.) A star with 20 times the mass of the Sun would be a(n): high-mass star 9.) Main sequence stars with more mass will be: hotter and brighter 10.) Which star will undergo the helium flash when helium fusion ignites? low-mass stars 11.) Protostars are powered by: the heat of contraction 12.) Which of the following is NOT true about the first reaction of the NCO cycle? It fuses...and a gamma ray 13.) A star with 6 times the mass of our Sun would be a(n): intermediate-mass star 14.) Our Sun is a: low-mass star 15.) A white dwarf (Type 1) supernova is the result of: a white dwarf building up enough helium to ignite fusion of helium with carbon.

Quiz 16, 17, & 18 answers

1. DArk matter is more likely to consist of: WIMPS 2. Most of the dark matter in elliptical galaxies is: in the centre 3. Most of the dark matter in the Milky Way is in: the halo 4. Our Local Group is part of the.....Clusters of galaxies: Virgo 5. Most of the dark matter in barred spirals is in: the centre bulge and bar 6. Which is true? 7. Which galaxies have little or no gas and dust? Elliptical 8. Why are spiral galaxies blue? Their gas & dust provides lots of star formation, so they have short-lived O- & B type stars 9. Which galaxies have more dust? Spirals 10. Which galaxies have distinct internal structure? spirals 11. Sa galaxies have: Large bulges and tight arms/ 12. Which galaxies are yellowish? elliptical 13. Early galaxies were: smaller than those today 14. Which galaxies have little or no new star formation? ellipticals 15. Which looks more round? An E0

Quiz 20,21,22

Speed is: distance per time Velocity is: distance per time, plus a direction The interaction needed to change an object's momentum is called: force Momentum is: mass times velocity If I move to a place with different gravity, what changes? my weight If I push two objects with the same force,a nd if they have different masses, they will accelerate at different rates. Which of newton's laws is this? Newton's second Law of Motion Which of Newton's laws argue that magic or divine intervention are not needed to explain motion? Newton's first Law of Motion When it drops a beaseball, it starts to fall, converting its (two words) energy into kenetic energy: gravitational potential The total kinetic energy of atoms and molecules in a material is called () energy: thermal Heat and temperature are the same? False The concentration of thermal energy in a material is called? temperature What is the melting point of ice in Fahrenheit? 32 degrees What is the condensation point of steam in Fahrenheit? 212 degrees your textbook has gravity? True -Anything with mass has gravity- Gravity is the strongest of the four known forces: False Which temperature scale is ultimately named after a river, by way of a man who lordship held the name of that river? Kelvin

Quiz 4

Eratosthenes (276 BC to 196 BC):

Researcher, librarian, and at one point head librarian of the Library at Alexandria founded by Alexander the Great. He is most noted for measuring the circumference of the earth by comparing noon shadows at Alexandria and Syene (near modern Aswan). Be sure you understand and can explain his method and calculations. He also measured the tilt of the Earth's axis, and invented the system of mapping the Earth using lines of latitude and longitude. (This is the same Eratosthenes you may remember from math class for having invented the Sieve of Eratosthenes, a method for discovering prime numbers.)

1. Electrons are: leptons 2. Astronomers have a scientific explanation for what caused the big bang. FALSE 3. Which class of particles can occupy the same space? Bosons 4. During which era did protons and neutrons first appear? The particle era 5. During which era did helium nuclei first appear? The era of nucleosynthesis 6. Gluons carry which force? The strong nuclear force 7. Electrons and quarks both belong to which class of particles? fermions 8. Protons are fundamental particles. FALSE 9. Photons carry which force? The electromagnetic force. 10. There is evidence to support the Big Bang theory? TRUE 11. Photons of light are: bosons 12. If i slam my finger in the door, my pain is caused by the application of which fundamental force? the electromagnetic force 13. Photons are: baryons 14. Which two forces were the first to be unified, in the early 80s? the electromagnetic force 15. A neutron is composed of: two down quarks and an up quark

S4,22,23 quiz

Saturn's moons:

Saturn is also known for an incredibly diverse suite of moons; one that spouts geysers into space from a buried ocean; one that hosts both the lightest and the darkest material in the Solar system, one with a mountain range ringing its equator, one that saved hundreds of thousands of lives, and likely has saved the life of someone you know. Three that share an orbit, and two that regularly swap orbits. Oh, and the Death Star is parked in orbit around Saturn

which one is the actual rotation period of the Earth?

Sidereal day

Greek word for "Star"

Sidereus (sidereal day)

During a solar eclipse, the Sun is hidden by the Moon. Naturally, this requires a new moon During a total solar eclipse, the surface of the sun is completely hidden and the corona, the sun's outer atmosphere, is visible. During a partial solar eclipse, the observer is in the penumbra, and the sun's surface is partially blocked There are several solar and several lunar eclipses each year. We don't see eclipses every full and new moon, because the Moon's orbit is tilted with respect to the Earth's. That means that usually the new moon passes above or below the sun, and the full moon passes above or below the Earth's shadow

Since the cone of the umbra is quite small (often only 10 or 20 miles across) where it reaches the Earth, an observer must be in just the right place, and the eclipse will last at most a little over 7 minutes There is a third case. If the Moon is especially far from the Earth (apogee), the umbra cone may not quite reach the surface. Then an observer beneath it will see the Moon centered on the Sun, but not quite covering it. The ring of Sun seen around the Moon gives this eclipse its name, annular (from the word annulus, or ring.)

Brightest star in the night sky is:

Sirius

When a planet is at aphelion, it is moving:

Slowest

a star-forming region in the Large Magellanic Cloud, a small satellite galaxy orbiting our own Milky Way galaxy

Star-forming regions start out as dense, massive clouds of gas and dust. When they are large enough, the outer parts shield the interiors from pervasive ultraviolet light in space, allowing molecules to exist. We call these "large clouds molecular clouds". If a molecular cloud is dense enough, gravity will pull the material in it into more tightly-packed clumps, each clump gets hotter as it's compacted. If a clump is hot enough to glow, we call it a "protostar". If the interior of a protostar becomes hotter than about 10 million Kelvin, the hydrogen nuclei begin to fuse into helium nuclei, and a star is born

On the first day of spring the sun will rise in the east. On the second day of spring, it will rise its own diameter, about half a degree, farther north The next day it rises a whole degree north of east Each day it rises farther north After a couple of months you start to notice it's not moving north as fast as it was Finally in summer, it rises in the same place for about four days in a row

Summer solstice comes from the Latin solstitium, which in turn comes from Latin Sol, the name of the Sun, + a conjugated form of the verb sistere, "to sit" Prehistoric people didn't have designations for east and west (they had six compass points instead of four) so the equinoxes were meaningless to them, but they could observe the solstices

The calculation also implies that the Earth's rotation would distort the shape of the Earth, flinging the surface outward at the equator by that same percentage

Take the radius of the Earth, multiply by that percentage, and we get a theoretical equatorial radial bulge of 27.4 miles

the Pleiades (seven sisters) star cluster is in:

Taurus, and the Summer Triangle which spans three constellations

The North Celestial Pole (NCP) is the point that would be at your zenith if you were at the North Pole. The South Celestial Pole (SCP) is the point that would be at your zenith if you were at the South Pole. Expand the equator out onto the sky and it becomes the Celestial Equator

The Celestial Equator rises precisely in the east and arcs across our southern sky reaching a high point at our latitude (36º) south of the zenith, then sets precisely in the west

Presented the following argument as to why Jupiter could not have any moons: ---------------------------------- "There are seven windows in the head, two nostrils, two ears, two eyes and a mouth; so in the heavens there are two favorable stars, two unpropitious, two luminaries, and Mercury alone undecided and indifferent. From which and many other similar phenomena of nature such as the seven metals, etc., which it were tedious to enumerate, we gather that the number of planets is necessarily seven. ... Besides, the Jews and other ancient nations, as well as modern Europeans, have adopted the division of the week into seven days, and have named them from the seven planets: now if we increase the number of planets, this whole system falls to the ground. ... Moreover, the satellites are invisible to the naked eye and therefore can have no influence on the earth and therefore would be useless and therefore do not exist."

The Florentine astronomer Francesco Sizzi, in 1611

Which of the following is NOT a factor in causing precession

The moon orbits the Earth at the same rate that the moon rotates

Aristotle (384 BC to 322 BC):

The most influential Greek scientist-philosopher. He rejected the Pythagorean's arguments for a mobile earth. He argued that we could not feel the motion of the earth, therefore it did not move. Further, if the earth moved, then we should be able to detect it by parallax that would make the stars shift and the constellations distort. What he did not know was that the stars were much further away than he could imagine and that the parallax he was looking for needed optical aid to detect. He did accept the spherical shape of both the earth and moon, and Eudoxus' idea of nested spheres. He also argued that the phases of the moon and solar eclipses demonstrated that the moon passed between the earth and sun making the sun more distant than the moon and larger. His ideas, and those of Plato, became important to Renaissance astronomers because they were incorporated into Roman Catholic theology in the 13th century by Thomas Aquinas.

The part of the universe of which light has had time to reach us is called:

The observable universe

Currently the North Celestial Pole is about one-and-a-half full moon widths away from Polaris, so Polaris is a decent marker for north

The pole will pass closest to Polaris in the year 2102, when it will be about two moon-widths away. After that, we can continue to use Polaris as a marker for north, with decreasing accuracy, for another 400 years or so. Sometimes the North Celestial Pole is passing through an empty patch in the sky, and there is no north star, just as there is no south star at the moment

Scientific Method ---------------------------- Many early civilizations used a system of priests or priestesses who told the average person what the deities said. Of course, one flaw in the system was that the deities only spoke to the priests, so if you're not a priest, how do you know if you're being scammed? logic systems was formalized by the Ancient Greeks. Deductive reasoning from the general to the specific, Example: "All astronomy students pay attention to the phases of the moon. I am an astronomy student. Therefore I know what phase the moon is in today." Inductive reasoning from the specific to the general, of the form "Garth and David are rude. Garth and David are men. Therefore, all men are rude." ---------------------------------------------- The operation of deductive logic is flawless, but the conclusions are only as good as the premises. In this case, the premise "All astronomy students pay attention to the phases of the moon." is incorrect. Some do, many do not. So the conclusion may be incorrect; you may not know the phase of the moon today. Inductive reasoning can be very useful. It is the basis behind much of "common sense", but it is not flawless. Both the cited premises may be correct, Garth and David may be rude, and they may be men, but that does not mean that all men are rude.

The reasoning tools of Greek logic are extremely powerful, and still form the basis for much of Western thought. They are widely applicable in science, philosophy, theology, sociology, and most other endeavors. But they are not perfect. As we saw in the above examples, they can lead to incorrect conclusions. By the late Middle Ages in Europe, a few people were coming to the conclusion that perhaps no one system of thought worked best in all cases; that different aspects of existence might yield to different logic systems. In particular, one way of thinking proved to be especially useful for studying the natural world around us. We see glimmerings of it in the writings of ancient Greeks such as Thales of Miletus. Roger Bacon in the 1200s espoused it. Galileo practiced it and drew attention to it in the early 1600s, and Newton formalized it in the latter part of that century. This way of thinking grew out of disillusionment with Greek logic and other forms of thought. Too many times in history, evidence seemed to prove an idea true. The idea would be accepted, only to have later evidence show it was false.

Our modern calendar is not the Julian calendar because of one further flaw that was not noted until much later. The actual length of the year is 365.2422 days. The Julian calendar (average length 365.25) is long by about 11 minutes per year

This does not sound like much, but it accumulates to one day every 125 years or about 3 days every 400 years. At the time of Julius and Augustus, the Vernal Equinox occurred on March 25. By 321 AD, the date of the Council of Nicea (more on this below), the Vernal Equinox was occurring on March 21

Newton's Law of Universal Gravitation is usually expressed as follows: Every object in the universe attracts every other object with a force that is directly proportional to the product of their masses and is inversely proportional to the square of the distance between them. where F is the force of attraction between the two objects (equal but opposite, see Newton's 3rd Law), G is the Universal Gravitation Constant (value is determined by the choice of units for the other quantities), M1 and M2 are the masses of the two objects, and R is the distance between them (expressed as the radius of the position of the second object from the center of the first). Each object will experience an acceleration towards the other according to Newton's 2nd Law.

This is usually presented as the following formula: F = G *M1 * M2/ R2

Kepler's Second Law (The Law of Areas) The radius vector sweeps over equal areas in equal times, or, planets move faster when closer to the Sun --------------------------------------- After Kepler had determined the shape of the orbits, he then concentrated on the motion of the planets on each orbit. It was quickly obvious to him that the speed was not constant. He noticed that planets tended to move faster when nearer the sun and slower when further. By 1610, he had found the relationship that accurately described the speed of a planet at each point on its orbit. The term radius vector is used for the line connecting a planet with the sun. It is like a radius except that the length changes with direction (a vector). He found that the radius vector swept over equal areas in equal times.

When the planet was near perihelion, the radius vector was short and the planet had to move faster to meet the condition. When the planet was near aphelion, the radius vector was long and the planet moved slower. The differences in speed were inversely proportional to the changing length of the radius vector. He recognized that this meant the Sun was exerting an attraction on the planets somehow, but didn't know what the cause of that attraction might be. At that time gravity was only recognized as the reason things fell here on Earth; nobody knew that the Earth's gravity might reach to the Moon, or that things besides the Earth might have gravity.

Kepler's Formulae for Perihelion and Aphelion Distances ------------------------------------- Once Kepler found that planet's orbits are elliptical, he apply use known mathematics for ellipses to determine how close a planet gets to the Sun, its perihelion distance, and how far it gets from the Sun, its aphelion distance. Perihelion distance = a(1-e) Aphelion distance = a(1+e) -------------------------------------------- In addition to astronomy and mathematics, he cast horoscopes and practiced law for a living

Where e is the eccentricity. Eccentricity is a number ranging from 0 to 1 that describes how flattened an ellipse is. An orbit with an eccentricity of zero is a circular orbit. An orbit with an eccentricity of 1 would be a line segment - the planet would just move back and forth on the line. Of course, this is impossible as a planet in such an orbit would crash into the sun! One hundred times the eccentricity is the percent deviation from a circle; a planet with an eccentricity of 0.03 has an orbit three percent off from being a circle. In our solar system, planets have orbits with very low eccentricities, typically just a few percent. Asteroids and Kuiper belt objects often have higher eccentricities, maybe 10% or more. Comets usually have very high eccentricities of more than 90%. Earth's eccentricity is 1.67%. When we are closer to the Sun, that makes the Sun look a bit larger. We are closest to the Sun in the first week in January, and farthest from the Sun in the first week in July. (No, that's not a mistake! Obviously our distance from the Sun is not the cause of our seasons. The difference in distance is too small to have much effect on our temperature.)

To complete his calendar reform, Pope Gregory wanted to drop ten days out of the calendar to bring the seasons back in step to what they had been at the time of the Council of Nicea. The reform was instituted in 1582 when October 2 was followed by October 13 instead of October 3. Of course special laws had to be passed to prevent landlords from collecting a full months rent for that month and other such inequities.

The Gregorian calendar reform came in the middle of the Protestant Reformation in Europe. Only the Catholic countries adopted the new calendar. The Protestant countries stayed with the Julian Calendar. Eventually, the improved accuracy of the Gregorian calendar was generally recognized and more countries began to adopt it

My favorite nebula is known as M42. Which naming system is this name from?

The Messier list

The Andromeda galaxy is also known as NGC 206. This name is from which system?

The New General Catalogue (wikipedia)

two reference points on Earth, the places where the rotation axis penetrates the surface

The North and South Poles

Here in the northern hemisphere, the sun rises farthest north on:

The Summer Solstice

Planet Atmospheres

The atmospheres of the Jovian planets consist of hydrogen and helium captured from the nebula in which the planets formed. Some of the terrestrial worlds (Luna and Mercury) don't have enough gravity to hold atmospheres. The remaining terrestrial planets, Venus, Earth, and Mars, originally had atmospheres composed of the gasses released by melting rock, mostly carbon dioxide and water vapour with a little bit of nitrogen. All three of these worlds had the water removed from their atmospheres, and Earth had its carbon dioxide removed as well; we'll see how this worked for each world. And of course, life produced oxygen on Earth

Declination measures how far a star is from:

The celestial equator

the places in the sky that the Earth's axis points to are called:

The celestial pole -Since the axis is moving, the North and South Celestial Poles move, tracing circles in the sky every 25,772 years. Whenever the North Celestial Pole passes near a star, we can call that star the North Star for a few hundred years, until the pole moves on

Just as the Earth's daily rotation causes the daily motion of things across the sky from East to West, so the Earth's annual revolution around the Sun can be seen in the sky

The constellation will appear in a different place. That's because your viewpoint (the Earth) has moved 1/12th of the way around in its orbit during that time. If you go out at the same time each night, the constellations appear to roll around the sky, taking a year to come back to their starting points. (This is called annual motion)

the seasons are due to the tilt of Earth's axis. in the northern hemisphere, the daily track of the Sun moves northward in the summer, and southward in the winter. The equinoxes are the only two days of the year when the sun rises in the east and sets in the west

The diagram below shows the the position of the Sun at sunrise on the summer solstice, seen from the latitude of Las Vegas. [The north/south white line is your meridian; there is a corresponding east/west white line - I don't know of a name for that one. Where they cross is the zenith. The east/west blue line is the celestial equator. (It crosses the meridian south of the zenith at an angle equal to your latitude.) You can ignore the north/south blue line. It's the zero-hour line of Right Ascension. I would have turned it off if the simulation had that option. Most important for us is the yellow line. It's the track of the sun for that day (the Summer Solstice). Notice how the sun isn't rising in the east, it's rising fairly far north of east. Throughout the day it will follow the yellow track, cross the meridian at noon, and set fairly far north of west.

The Moon rotates at the same rate it revolves, so we only ever see one face, the nearside

The farside was "luna incognita" until a Soviet spacecraft sent back the first pictures

Apollonius of Perga (Dates uncertain, but between Eratosthenes and Hipparchus):

The first to suggest explaining retrograde motion via epicycles rather than nested spheres. Developed the mathematics of the conic sections (circles, ellipses, parabolas, and hyperbolas that Newton would later use in describing how the shapes of orbits are dictated by gravity.

there is more than one way to define a year. The table below is taken from David Ewing Duncan's 1998 book Calendar from Avon Books

Year / Length of Year 2000 (in days) -Sidereal / 365.2564 -Mean Tropical / 365.24219 -Between two vernal equinoxes / 365.24237 -Between two summer solstices / 365.24162 -Between two autumnal equinoxes / 365.24201 -Between two winter solstices / 365.24274

Terry Pratchett said it well in The Globe: The Science of Discworld II when describing the task of a scientist:

You might imagine that what she should be trying to do here is to prove her [hypothesis] is correct. However, that's not good science. Good science consists of designing an experiment that will demonstrate that a [hypothesis] is wrong - if it is. So a large part of the scientist's job is not 'establishing truths', it is trying to shoot down the scientist's own ideas. And those of other scientists. This is what we mean when we said that science tries to protect us against believing what we want to be true, or what authority tells us is true. It doesn't always succeed, but that at least is the aim." In a footnote, Pratchett goes on to talk about the way pop culture frequently misunderstands the function of science. "On TV news [and online] we are repeatedly told about scientists who are 'proving'[an idea]. Either the people making the programme [or website] were trained in media studies and have no idea how science works, or they were trained in media studies and don't care how science works...

The angle between the North Celestial Pole and the horizon determines:

Your latitude

We are closest to the Sun (perihelion) in early January

and farthest away (aphelion) in early July.

Copernican Revolution

archaeoastronomy*, the study of what prehistoric cultures knew about astronomy Galileo: Used observations with a telescope to support Copernicus' arguments, and wrote a book popularizing the heliocentric model. We'll also look at his studies of how gravity affects falling objects, and at his use of the scientific method. Kepler: Promoted Copernicus' idea, and used Tycho's data and his own mathematical insights to improve the heliocentric model by using elliptical orbits Tycho: His extremely accurate data on planetary motion was used by Kepler Copernicus: Revived heliocentrism. Be particularly careful in considering the cause of retrograde motion. This was key to Copernicus' arguments Ptolemy: Make sure you understand how his model accounted for retrograde motion

1. How long does a typical species last? 10 million years 2. looking at the span of geologic history, life on earth arose very early on, making it likely that life starts easily when conditions are suitable. TRUE 3. Looking at the span of geologic history, complex multicellular life (plants, fungi, animals) on earth arose very early on making it likely that complex life starts easily when conditions are suitable. FALSE 4. we believe that most stars have planets. TRUE 5. We believe that most stars are suitable to host life. FALSE 6. I would like 75 free points. YES

chapter 24 quiz

the knowledge that the Earth rotates once a day, combined with an understanding of the equatorial coordinate system, tells us that stars will seem to describe daily circular paths across the sky, parallel to the celestial equator is called:

daily motion

Sidereal year is

measured against the stars (meaning the time it takes the sun to return to the same spot on a starchart) so its the actual period it takes the earth to orbit the sun

The traditional answer is somewhen around 11,500 years ago in the Tigris-Euphrates Valley (Mesopotamia), though virtually everyone in the research field has their favourite earlier example. Barley may have been the first crop, but the traditional eight early ones were hulled barley, emmer wheat, einkorn wheat, peas, lentils, chick peas, flax and bitter vetch

most prehistoric societies were well aware of the seasonal change in the Sun's daily track, and used observations of the solstice dates to adjust their calendars as needed

Stars shine by:

nuclear fusion (by fusing lightweight atomic nuclei into more massive atomic nuclei in the star's core. All stars begin by fusing hydrogen into helium)

How long does it take the Earth to rotate

one day

Tycho Brahe (1546-1601) Tycho observed the relative positions of stars looking for heliocentric parallax that would be caused by the motion of the earth around the sun. His observations were limited only by the limit of resolution of the eye (about 1 arc minute). He correctly observed that either the earth was stationary or the stars were at least 7000 times further away than the sun (the nearest star is actually 270,000 times farther away). However, he went on to conclude that 7000 times the earth-sun distance was so great that it could not possibly be true and concluded that the earth was stationary.

in the 16th Century, Tycho Brahe rose as the greatest observer prior to the telescope. The son of a minor Danish nobleman, At the age of 20, he became famous by using parallax to show that a new star that appeared in the sky was not in the atmosphere, but was indeed in the heavens. His fame got him appointed Astronomer Royal by the King of Denmark, but when the king actually met him (after he accepted the post), the king took a great disliking to him. To save face, the king honored the job offer - but not at the royal court. Instead, Tycho was granted the island of Hveen ("Heaven") off the north coast of Denmark. Here he built the most precise pre-telescope observatory ever built. The observatory was named Uraniborg. From the mid-1570's until he fell out of favor with the Danish court, Tycho amassed an incredible series of observations.

equatorial coordinate system

is related to the latitude and longitude system used on Earth, other planets, and moons

England and its American colonies switched in 1754. Since another day of error between the calendars had crept in, 11 days had to be dropped. September 4, 1754 (Julian calendar) was followed by September 16, 1754 (Gregorian Calendar). Similar protective laws were passed, but people still felt they were being cheated out of eleven days of their lives. There were even riots ("Give us back our fortnight")

it is not unusual to see dates followed by "N.S." for New Style (Gregorian calendar) or "O.S." for Old Style (Julian calendar). Today we celebrate George Washington's Birthday on February 22. However, when he was born in 1732, a calendar on the wall would have read February 11 since the Julian calendar was in use at that time. Sometimes during the transition, both days would be combined. An invitation to George Washington's birthday party in 1755 could have had the date written as February 11/22, 1755.

Messier list of items

-M1 through M110 (techincally there is only 109) -Charles Messier was a comet hunter -it's a popular list of the best and brightest targets for binoculars and backyard telescopes

24 equal periods are called:

hours

Greek alphabet has:

only 24 letter

the Year of Confusion

-44 BC -the year was given over 440 days in order to shift the old Civil Calendar into the new Julian Calendar -its how december went from being the 10th month to the 12th month.

Earlier in the chapter, the concept of the electromagnetic spectrum was introduced. We shall now look at the origin of that spectrum and how we can use it to study the rest of the Universe. Isaac Newton was the first to demonstrate that the colors produced when light passed through glass or water (a rainbow) were part of the nature of the light itself and not something added to the light by the substance it passed through. White light is a combination of all of the other colors. Those colors, in order of decreasing wavelength, are Red, Orange, Yellow, Green, and Blue. It is important to know this sequence. By the beginning of the 19th Century Joseph Fraunhofer noticed that when expanded, the Sun's spectrum showed a series of dark lines. Fraunhofer could not explain the origin of these lines. The most prominent lines in the solar spectrum are still called Fraunhofer lines. You can see lots of them in the spectrum of the Sun at the beginning of the textbook chapter. -----------His results are today summarized as Kirchoff's Laws.------------ Kirchoff's First Law A continuous spectrum arises from a hot solid, a hot liquid, or a hot high-pressure gas. Kirchoff's Second Law An emission spectrum arises from a hot gas at normal pressures. Kirchoff's Third Law An absorption spectrum arises when a continuous spectrum source is viewed through a cool gas. The book has a diagram illustrating Kirchoff's laws, showing how each spectrum is produced. Two very useful facts were eventually noted about spectra. Each chemical element produces a unique emission spectrum. This was a great boon to chemical analysis. It was now possible to take every element on the periodic table, dissolve it in acid, squirt a mist of that acid in a flame, send the resulting light through a spectroscope, and record the spectrum of each element. Now an unknown material could simply be dissolved and its spectrum noted, and its constituent elements could be identified by comparison with the library of known spectra. In the case of hit-and-run accidents, for example, a fleck of paint left at the scene can help police identify the make, model, year, and dealer of the car involved. The second useful fact is that the emission spectrum and the absorption spectrum of each element are complementary. The same wavelengths that are present in the emission spectrum will be the ones missing from an absorption spectrum. This meant that scientists only had to record one of the two types of spectra to know what the other would look like. Astronomers learned that about 90% of all stars show absorption spectra; their surfaces are at sufficiently high pressure to produce continuous spectra per Kirchoff's first law, but their atmospheres are cool enough to obey Kirchoff's third law. About 10% of all stars have sufficiently hot atmospheres to produce emission spectra, per Kirchoff's second law. Still, there were many fundamental questions unanswered. Why did hot solids give continuous spectra? Why were emission and absorption spectra complementary? Why did the emission spectrum of sodium consist of two yellow lines, while that of hydrogen was a red, a green, a blue, and many violet, and that of neon had many reds and oranges and a yellow? Nobody knew, and the questions were becoming important. Chemist knew the periodic table was incomplete. There were gaps, undiscovered elements. If their spectra could be predicted, perhaps we could find them. The opposite problem also existed. It was an embarrassment that one of the most prominent sets of spectral lines in the solar spectrum could not be identified. Was there an element on the Sun that was not found on Earth? If it was on Earth, where was it? Was it a solid, liquid, or gas? Should we look in sea water? In rocks? In air? We named it helium after the sun god Helios, but had no clue what it was like or where to find any. Two generations of scientists tried to find the missing link between the identity of an element and the wavelengths in its spectrum. They wasted their time. They might as well have tried to predict how many raindrops will fall next year. The key lay in the internal structure of the atom, and that, they did not know

Chapter 5 (Spectroscopy Interaction of light and matter

We've made it sound like spectroscopy is fairly simple. To do chemical analysis on stars, all a scientist would have to do would be to document the spectra of the 90 stable chemical elements, then examine the spectrum of a star to see which elements are present. In practice, there are a huge number of complications, but astronomers regard that as a good thing. If temperature and magnetic fields for example, can change the spectra, that means the spectrum can be used to study the temperature and magnetic field of the star. Let's look very briefly at a few of these complications, and how we can use them. Changing the ionization state of an atom changes the spectrum. Remember that an ion is an atom with an electrical imbalance, it does not have the same number of electrons (-) as protons (+). In stars, the major cause of change in the ionization state is temperature. Studying the ionization of stars by spectroscopy has been turned into a very accurate way to take their temperatures. Wien's Law can determine the temperature of a star ±100°, but ionization studies can often make the determination ±10°. Since the surfaces of stars tend to be much hotter than typical temperatures on Earth, atoms in stars typically exist in high ionization states not normally found on Earth. Scientists have had to make special studies of the spectra of elements at very high temperatures in order to understand stars. Another possible complication in spectroscopy is that the spectra of molecules is nothing like the spectra of their constituent atoms. A molecule is a collection of atoms chemically bonded together, either by swapping or sharing of electrons. This completely rearranges the spacing of the orbits, resulting in a new spectrum. The spectrum of water, H2O, is nothing like the spectrum of either hydrogen or oxygen. Molecules are quite rare in the high-temperature environments of stars, but exist in interstellar gas and dust clouds. There are many millions of possible molecules, so identifying the ones floating in distant space isn't always easy. If all the atoms contributing to a star's spectrum were under identical conditions, the wavelengths each one absorbed or emitted would be identical, and would superimpose exactly on each other, giving a spectrum with sharply defined lines. However, many factors can shift the wavelengths slightly, so the combined light from the star shows lines that are noticeably broadened. Spectral lines can be broadened by high temperature, pressure, magnetic field strength, rotation speed, and many other factors. It's not always possible to decipher which factor is broadening the lines of a particular star, but if we can figure it out, that's one more piece of information we know about that star. Of course our Solar system has only one star. What about the spectra of planets? In the visible, UV, and much of the IR portion of the spectrum, the light from a planet is simply reflected sunlight. We already know that sunlight is an absorption spectrum, but reflecting that light off a planet will add additional absorption lines. So the spectrum of a planet will be an absorption spectrum. Whichever absorption lines aren't found in plain sunlight, must belong to the planet.

Chapter 5 (Sprectral complications)

Today we know what the spectroscopists of the late1800s did not - the internal structure of the atom. For our purposes, we can stick to a simplistic model in use 70 years ago, the Bohr atom, a model devised by the Danish physicist Niels Bohr. We need only consider three of the atom's constituent particles: the proton, the neutron, and the electron. The fact that the protons and neutrons are composed of up and down quarks need not concern us, any more than the soup of gluons and virtual quarks that surrounds each quark, or the sea of virtual mesons which fills an atom. And of the eight fundamental properties that define any subatomic particle, only the charge and the mass are important here. The electron has a negative charge, the proton has a positive charge, and the neutron has no charge; i.e., it is neutral (hence the name.) The electron has a tiny mass. The neutron and proton have similar masses, which are over 1800 times that of the electron. The neutrons and protons of an atom are tightly packed in a dense central region called the nucleus. The electrons circle around this nucleus at relatively great distances, leaving most of the atom as empty space. If we shrunk a typical atom to the size of the Rose Bowl, the nucleus would be the size of a strawberry lying on the 50 yard line, with the electrons as dust specks circling in the upper stands. In an electrically neutral atom, the numbers of electrons and protons are the same. If they are not balanced, an electric charge results, and the atom is said to be ionized, turned into an ion (an electrically charged atom.) The Bohr model's image of a large central mass (the nucleus) with many much smaller masses orbiting it is sometimes known as the planetary model in analogy to the Solar system. The analogy doesn't fully hold, however. Electrons follow different rules than planets. For example, a planet can exist at any reasonable distance from its star, but electrons are restricted to particular distances; it is impossible for them to orbit between those particular distances. The unusual rules that govern electron behavior are collectively known as quantum mechanics. The quantum mechanics rules in their full mathematical form are complex, and well beyond the scope of this course, but most of them can be stated simply in words. ------The ones we will need are these:--- *An electron can have only certain amounts of energy, which means it can orbit only at certain distances from the nucleus. *An electron must lose energy to move closer to the nucleus, and must gain energy to move away from the nucleus. One of the ways it can do this is by emitting or absorbing light. *An electron will tend to move to the state of lowest energy, i.e., closest to the nucleus. *Each orbit can hold only a certain number of electrons. Those farther from the nucleus hold more. *The spacings and energy differences of the orbits are different for each element, and for each ion state of each element. Absorption Spectra---------------- The first diagram below depicts an electron absorbing energy from light and moving from the innermost orbit to the second orbit. For this hypothetical element, the amount of energy needed to make this particular transition is the amount contained in yellow light. Any other color of light would not result in this transition. In the second diagram, An electron in the second orbit absorbs energy and moves to the third orbit, an amount of energy equal to that contained in red light. The same electron could make both transitions sequentially, starting in the first orbit, absorbing some red light to jump to the second, then absorbing some yellow light and continuing on to the third. It's important to remember that I'm making these colours up. Atoms of a different chemical element would have different colours for the same jumps, so don't fall into the trap of thinking that moving between the first and second orbit always involves yellow light! Or, an electron in the first orbit could absorb even more energy from light of shorter wavelength (say, blue), and jump straight to the third orbit. In no circumstances could the electron end up between the orbits. If I had a collection of these atoms, and bathed them in white light, some of the atoms would absorb red light, some yellow light, and some blue light. Hence, the absorption spectrum of this element would have three dark lines in the red, yellow, and blue. Since each element has atoms with different orbital spacings, each element will have a characteristic absorption spectrum. Emission Spectra--(red wave to the right) The process for producing emission spectra is similar, except that the electrons are moving inward toward the nucleus, and must give off energy, which they can do be emitting light. If an atom of our hypothetical element has an electron in the third orbit, and if there are empty spaces in the first and second orbits, the electron can proceed in one of two ways. It can jump initially to the second orbit, then to the first, resulting in flashes of red and yellow light, ... ... or, it can move directly from the third to the first orbits, giving off blue light. In a collection of such atoms, some will follow each path, resulting in an emission spectrum of red, yellow, and blue light. The image below illustrates the utility of this in a chemistry lab. The Petri dishes are filled with a flammable alcohol, and each one contains grains of a different salt (likely the chlorides) of the metals listed. The heat from the flame provides energy to the electrons of the metal atoms, causing the electrons to move away from the nucleus. They then emit light as they come back down, each emitting colours of light characteristic of their particular elements. Remember that about 90% of all stars show absorption spectra, while the other 10% show emission spectra. This is because the visible surfaces of most stars have sufficiently high pressure to follow Kirchoff's First Law and produce a continuous spectrum. That light then has to shine through the cooler outer atmosphere. In that area, the cooler temperatures mean that electrons tend to have less energy, and lie in lower orbits. They can absorb energy from the emerging light; the result is an absorption spectrum. About 10% of the stars are so hot that the electrons of atoms in their atmospheres are mostly in outer orbits, and occasionally jump inward, giving emission spectra.

Chapter 5 (the atom)

By solar activity, we mean the sunspots, prominences, and solar flares we see on the surface of the Sun. These can influence the flow of gas in the solar wind, which in turn can have effects on Earth, and especially on our technology. ----sunspots and the solar cycle---- Sunspots are dark spots that appear on the face of the Sun and last for hours to over a month. You saw a picture of one on the previous page, but they're not all round like the one in that picture. Since the Sun is glowing gas, it should be obvious to you by now why the sunspots are darker. Think Stefan's Law. That's right, they're cooler. The umbra of a typical sunspot is about 1,000 K cooler than the surrounding photosphere, so they glow a dim orange instead of a bright yellow. As a matter of fact, many pictures of sunspots are properly exposed for the surrounding photosphere, so the umbra looks black in those pictures. But of course, saying sunspots are dark because they are cool simply begs the question. Why are they cool? We have spectroscopic evidence that they are cooler because they have strong magnetic fields. For certain types of atoms, their absorption lines split into multiple lines in the presence of strong magnetic fields; the stronger the field, the wider the separation of the split lines. This is known as the Zeeman effect. The spectroscopy of light from sunspots shows they have magnetic fields about a thousand times stronger than those of the surrounding photosphere. But it seems we're just replacing one mystery with another. OK; sunspots are dark because they're cool, and they're cool because they have strong magnetic fields. Why do they have strong magnetic fields? Our best hypothesis at the moment, and there is reasonable evidence to support it, has to do with the way the Sun rotates. Recall that the Sun is not a solid object; it's a ball of gas. Most rotating spheres of fluid, whether liquid or gas, undergo differential rotation; that is, they rotate faster at the poles than they do at the equator. We see this in stars, Jovian planets, raindrops, et c. So what does this have to do with sunspots? Think back to Chapter 4. Recall that a plasma is an ionized gas, and the Sun is hot enough to ionize the gasses there. If a gas is not ionized, it's independent of any magnetic field; on Earth the blowing wind doesn't carry the Earth's magnetic field with it, and when the Earth's magnetic field moves it doesn't carry the wind with it. That's not true for an ionized gas; move an ionized gas, and the electric charge on the atoms drags the magnetic field with it. Now think of the Sun, where the gasses at the equator are moving faster than those near the poles. They drag the Sun's magnetic field with it, so the magnetic field gets more wound up as time goes on. That stores energy, just like winding the spring of a watch or clock. Calculations show that the Sun's magnetic field can be wound up for about 11 years before so much energy is trapped in the tightly-wound field that dramatic things start to happen. Kinks develop in the magnetic field, areas of intense magnetism, which would produce pairs of locations with intense magnetic fields, one of each pair being a magnetic north pole, the other a magnetic south pole. The intense magnetism at these areas would lead to cool spots on the surface. Over a period of a few years, these kinks would release all the stored-up energy in the magnetic field, returning it to its unwound state. But the differential rotation continues, so after another 11 years, the same thing would happen. This is indeed what we observe. Sunspots occur in pairs, with the members of each pair having opposite magnetic polarity. Take a look at the graph below, which shows sunspot activity versus time for the last four centuries. Blue data is from observatories, red data is from naked-eye observations at European monasteries. It's evident that the sunspot intensity comes and goes in a cycle of roughly 11 years. As I write this in the autumn of 2020, we are just beginning to emerge from the latest minimum of the cycle. [Update in summer of 2022; the cycle now beginning is proving to be stronger than predicted.] But it's also evident that the individual 11-year cycles are not equivalent; some are much more intense than others. We don't fully understand why. There are mathematical models that have been able to successfully predict that the last two minima would be less intense than usual, but those models have not been able to explain the past 400 years of behaviour. It's also very mathematically complex; it's beyond my understanding, and I've yet to find an explanation in terms that I can understand and pass on to you. If you have a differential equations course under your belt, here's a good summary. image saved (red and blue ekg) Another success of these so-called magnetohydrodynamic models is that they describe how sunspots at the beginning of each 11-year solar cycle should appear at high latitudes far from the Sun's equator, then progress toward the equator during each cycle. This behaviour was first noted in the 1800s by the Northern Irish astronomer Annie Maunder. She and her husband published a graph similar to the one below, plotting latitude against time. She noted the resemblance of the pattern to butterfly wings, and the graph is now known as a butterfly diagram. inage saved (butterfly type image) So, do sunspots affect the Earth? No and yes. They don't change the amount of light and heat we get from the Sun. Recall that the Sun's energy is generated in the core, and has to filter up through the RTZ and the CZ. When hot gasses bubbling up through the convective zone encounter a sunspot, they just go around it. The result is that the area around a cool, dark sunspot is a bit warmer and brighter, and the total light and heat output from the Sun doesn't change. We've known about sunspots since at least the time of Ancient Greece; generations of scientists have spent much time and effort looking for anything on Earth that fluctuates with the 11-year sunspot cycle, in vain. We've checked heat waves, cold snaps, tornadoes, hurricanes, floods, ocean currents, population cycles, even sociological factors such as crime and economic statistics. We have not found any reliable connections; nothing on Earth seems to follow the 11-year solar cycle. Abd yet sunspots may affect the Earth's atmosphere; not the weather, but the climate. Go back to the first diagram on this page, and you'll notice the almost complete lack of sunspots in the late 17th and early 18th centuries. It was Annie Maunder who described this while studying monastery sunspot records, and the time period is now known as the Maunder Minimum. Interestingly enough, it roughly corresponds to a time period in climate history known as the Little Ica Age. The Little Ice Age was not an ice age, just a cold spell that lasted several decades. But of course, correlation does not imply causation; the two events could be unrelated. Researchers at the Desert Research Institute in Las Vegas investigated the last 40,000 years and found six other times when the climate got cooler, and six other times when the sunspot cycle shut off. Five of them matched. One of the cool spells was unrelated to a sunspot cessation, but was instead caused by volcanic ash from the eruption of Mt, Tambora. And one of the periods when the sunspots shut off had no corresponding cool spell. But how could turning off the sunspot cycle cool the Earth, since sunspots don't alter the Sun's light and heat output? A team of researchers at the University of Colorado at Boulder has found that sunspots increase the amount of ultraviolet light from the Sun. Ultraviolet light destroys ice crystal in cirrus clouds in the upper atmosphere, so they have hypothesized that when the sunspot cycle shuts off, cirrus clouds accumulate, shading and cooling the Earth. This hypothesis is indirectly supported by studies of landscape paintings during the Maunder Minimum/Little Ice Age. This period in European art history is known as the Dutch Golden Age, and landscape paintings not just from Europe, but also from China and Japan, show a preponderance of paintings with overcast skies. The jury's still out, however, as the Little Ice Age began a bit before the Maunder Minimum. ------Prominence and solar flares-------- Three other phenomena associated with solar activity are quiescent prominences, active prominences, and solar flares. Recall that sunspots occur in pairs with the sunspots of each pair having opposite magnetic polarity. Prominences are arches of gas lifted above the surface of the Sun by the magnetic fields between the sunspots in a pair. Sometimes the magnetic field is stable, and the result is a quiescent prominence like the one in the 5-o'clock position in the video below. These have no effect on Earth. But sometimes the magnetic field is unstable and can expand outward, flinging the gas in an active prominence away from the Sun to become a gust in the solar wind, a Coronal Mass Ejection. The Earth has a magnetic field that normally deflects the solar wind around much of the Earth, only allowing it to reach the top of the Earth's atmosphere in rings around the Earth's north and south magnetic poles. When high-energy electrons in the solar wind strike atoms in the Earth's atmosphere, they can cause electrons in those atoms to gain energy and move away from the atomic nuclei. As the electrons return to their vacated orbits, they can emit light, as we saw in Chapter 5. Oxygen emits green or red, depending on how the electrons move, while nitrogen emits blue. The resulting light is the aurora, the northern and southern lights. When a gust in the solar wind reaches the Earth, it can cause the aurora display to be more intense. It can also deform the Earth's magnetic field, causing the aurora to be seen closer to the equator. Aurora were seen here in Las Vegas a few years ago during the last solar maximum, but because they happened early in the morning, few people were aware of them. Of course, deforming the Earth's magnetic field causes compasses to point in different directions, and can induce electric currents in wires, damaging satellites and causing power surges in our electric distribution grid. Even more impressive is a solar flare. These are explosions that occur near some sunspots; they are caused by the sudden collapse of complexly-tangled magnetic fields, and release considerably more energy than hydrogen bombs. We can't predict particular ones, but they are more common and larger near solar maximum in each cycle. The bright flash seen near the 4-o'clock position in the video below, with the resulting spray of material, is a solar flare. Intense solar flares present a radiation hazard to astronauts, and even to airline passengers. They can cause aurorae to be seen all the way to the equator, and can rip off the Earth's magnetic field (which will rebuild over days). As the Earth's magnetic field is rapidly deformed, strong electric currents can produce electric power blackouts, fry electronics, and disable satellites. We don't know how strong a solar flare our Sun can produce. The strongest to strike Earth in recent history was the Carrington Event of 1859, which caused extreme aurorae, telegraph failures, and fires. Although there were electric telegraphs and a few very limited electric power distribution grids at the time, electronic devices had not yet been invented. It's believed that such an event today would destroy virtually every electronic device on Earth; computers, TVs, cell phones, ATMs, the computer chips in cars and cash registers. The effect on civilization would be catastrophic. Lloyds of London has estimated the cost in the tens of trillions of dollars. In 2012 such an event just missed Earth by hours. It's the main reason why a large portion of NASA's Solar System Exploration budget is devoted to the study of the Sun; we really need to learn how to predict solar flares!

ch 14 our star, sol, the sun- its activity and its effects on earth

The path the Sun follows across the sky in the course of a year (which is really just a projection of the Earth's orbit onto the sky) is called:

the ecliptic

The halfway between the north ans south pole is called:

the equator

Copernicus

the number system we call "Arabic numbers" was invented by Hindu mathematicians in India (who also invented the concept of zero, a symbol to stand for nothing) This enabled the creation of the positional number system we use today, where the symbol "1" can mean 1, 10, or 100, et c., depending on which position it occupies in a number. This makes calculations much easier than they were in Roman numerals, and in particular made division simpler, and more accessible to many people. The Islamic world adopted these innovations and passed them on to us (which is why we call them Arabic numerals) Also during this time the Islamic world produced more accurate star charts, made more accurate measurements of things like the tilt of Earth's axis and the rate of precession, and used those improved measurements to improve the accuracy of Ptolemy's model.

The part of the universe we can see, the part from which light has had time to reach us is called:

the observable universe

rotate means:

to move around an axis passing through the object itself; the Earth rotates once a day around an axis passing from the North Pole though the center of the Earth to the South Pole

revolve means:

to move around something else; the Earth revolves once a year around the Sun

Nicolas Copernicus (1473-1543)

was a Polish monk who was a young student when the New World was discovered. Copernicus was trained in classical astronomy, mathematics, medicine and economics. He served as a cleric, administrator and diplomat. In his studies of astronomy, the use of equants by the Ptolemaic system particularly bothered him. He felt that it should be possible to describe the motions of the planets more simply

sky is not a surface

we use imaginary surface the "celestial sphere"

Wein's Law says

when things are hot enough to glow, the cooler one glows red, and the hotter one glows blue.

Kepler's First Law (The Ellipse Law) Every planet orbit is an ellipse with the sun at one focus ------------------------------------ Using the relationship between the synodic and sidereal periods of a planet, Kepler determined the sidereal period each planet needed to circle the sun. That relation is: 1/P = 1/E + 1/S for an inferior planet (Venus & Mercury) or 1/P = 1/E - 1/S for a superior planet (Mars, Jupiter & Saturn)

where E is the sidereal period of the earth (1 year), S is the synodic period of the planet and P is the sidereal period. We observe the synodic period of a planet by measuring the time from one conjunction to the next similar conjunction or the time from one opposition to the next opposition. Using the above formulas, we can then determine the sidereal period of each planet. As an example, the synodic period for Mars is 2.135 years. Thus 1/P = 1/1 - 1/2.135 or 1/P = 1 - 1/2.135. Solving this equation gives us P = 1.881 years. (A similar calculation can be made for each planet.)

Kepler's Third Law (The Harmonic Law) The square of the sidereal period is proportional to the cube of the average distance from the Sun. ----------------------------------- For nearly 10 years (1610-1620) Kepler tried to find some relationship between the relative positions of the planets from the sun. He was generally unsuccessful in this. While he was at it, however, he did find a relationship between the average distance of a planet from the sun and its sidereal period. This became his third law. The third law is usually expressed as: P2 = a3

where P is the sidereal period of a planet in years and a is the semimajor axis (average distance for the sun) of the orbit in Astronomical Units (AU) or the average distance of the earth from the sun). The farther from the sun a planet is, the slower it's average velocity.

Henry Draper catalog

stars are designated with the initials HD followed by sequential numbers, but the HD Catalog is more than just a map and a list of stars. It contains many facts about each star, such as its brightness, temperature, distance, rotation rate, magnetic field, etc

If you live in a temperate zone, your planting season is temperature-dependent. Plant too soon, your seedlings may be killed by a late frost; plant too late, an early frost may destroy your crop before it ripens; either way, you go hungry. Two bad years in a row, and your population's in trouble If you live in the tropics, your planting season may be determined by a wet/dry season cycle. Plant too soon, your seedlings die before the rains come; plant too late, your crop withers before it ripens.

synodic month (average length is 29.53 days) a purely lunar calendar based on it usually alternated between 29-day months and 30-day months. Twelve of those months gives a 354-day year, more than 11 days short of the actual year length of 365 and just under a quarter days early agricultural societies developed luni-solar calendars, with 11 intercalary days inserted in various ways.

Altitude and azimuth...

the Altitude and azimuth coordinate system (which specifies how far something is above the horizon (its altitude) and which direction to look (using the Arabic word for direction, azimuth.) -Altitude is specified in degrees, with the horizon being 0º and the point straight overhead (known by the Arabic word zenith) as 90º. -A north/south line through the zenith is called "the meridian". -Azimuth can be specified by compass directions (north, south-southwest, etc.) or more precisely using degrees. When degrees are used, the measurement begins from the north and proceeds eastward, so North is 0º, East is 90º, South is 180º, West is 270º, etc. -The zenith is in the center of the picture, the concentric circles connect points of equal altitude, the radial lines connect points of equal azimuth

There are 2 trillion galaxies in the observable universe, the part of the universe from which light has had time to reach us since the Big Bang. Are they all like ours? No. GALAXY CLASSIFICATION Our galaxy classification scheme basically divides galaxies into spirals and ellipticals, Edwin Hubble came up with the system we use, although it's been modified since his day. It's not as satisfactory as our stellar classification system, and continues to be modified. SPIRALS Spiral galaxies are the ones we all think of when we think of a galaxy; a disk with spiral arms, a central bulge, and a halo. Until fairly recently, we assumed our Milky Way galaxy was a spiral. *(It turns out to be a barred spiral.) Spirals have lots of gas and dust, the raw material that forms stars, so they have lots of star formation, and lots of new stars. -Spiral galaxies are designated with a capital S. The direction in which the arms spiral is NOT related to the direction the galaxy rotates; Disk galaxy: the arms are stirred up by passing galaxies, and their direction determined by the direction of passage. whether or not one has spirals depends on the neighbourhood. There are four subclasses of spirals; Sa, Sb, Sc, and Sd. (Hubble's original scheme only ran Sa through Sc.) *Sa galaxies have large central bulges and tightly-wound arms, *Sd's have small bulges and loosely-wound arms. -Intermediate classifications are also used, Sab, Sbc, and Scd. The photo below is of the spiral galaxy M106, an Sbc. (galaxy with red spiral in the middle and 2 bright stars in the front) lifespan of stars**** -Cool stars, that are dim and either orange or red, last a long time. -Hot O- and B-type stars, that are bright and blue, don't. So if star formation is ongoing, there's a constant supply of bright blue O- and B-type stars. They outshine the others, so spirals tend to look bluish. LENTICULARS Lenticular galaxies: a large central bulge that resembles an elliptical galaxy, with a disk extending out from that, but no spiral arms, so in shape they are intermediate between spirals and ellipticals. Just Like ellipticals they lack significant amounts of gas or dust, and so have little or no star formation, appearing mostly yellowish. *They are designated S0. Since a lenticular galaxy seen face-on will look like an elliptical, galaxies that are classed as E0 through E3 may actually be lenticulars, or vice versa. (looks like fishes in the ocean) DARK MATTER (looks like pink purple stars) *most of the matter in the Milky Way is dark matter; (meaning, matter that can't be seen at any wavelength. Back in the '80s: two major competing ideas. 1. One idea was that dark matter was cold and in dark places, so maybe it was made of things like large planets far from stars. To remain undetected, and to fit the gravity profiles of galaxies, they would have to be out in the galactic halos. They would have to be massive, and compact, or we would have seen them already. These were termed MAssive Compact Halo Objects, MACHOs. 2. The second possibility was that dark matter was not composed of protons, neutrons, and electrons at all; that it consisted of new types of subatomic particles we hadn't discovered yet. They would need to be massive, about as massive as a bacterium, and since they obviously didn't interact via the electromagnetic force (or we would see them) or via the strong nuclear force (or they would be found in atoms), they were termed Weakly-Interacting Massive Particles (WIMPs). The current difficulty is that lots of searches have pretty much eliminated the MACHOs, and ongoing searches are rapidly eliminating the various hypotheses for WIMPs. So either dark matter will turn out to be one of the few remaining proposed WIMP ideas, or some variety of WIMP we haven't thought of yet, or something else entirely. Either way, it's quite embarrassing for scientists to learn that for the past 400 years, we've built up a science that was only studying the less common type of matter in the universe. We've learned a little bit about where dark matter is. It's not evenly distributed throughout the universe. Since it interacts through gravity (that's how we discovered it), it is clumped in the galaxy clusters. Within different types of galaxies, it's distributed differently. In spiral galaxies it's concentrated in a shell around the visible galaxy. In elliptical galaxies it's concentrated in the centre. In barred spirals it's concentrated in the centre, and seems to end where the bar makes its turn to become the spiral arms. I've found little information about its location in lenticular or irregular galaxies. ACTIVE GALAXIES Remember those supermassive black holes in the centres of most galaxies? Would you like to know how they fit into the story of galaxy evolution? So would we. We know that they were present in most galaxies at a very early stage. Did they form from the dark matter? Did they form as early Population III stars were born and died in the centres of young galaxies? Did they form as stars, crowded into the centres of young galaxies, merged? That last idea was once the most popular, but observations and models have made it less so. It's very much an active research question at the moment. But the fact that the supermassive black holes were there early in the history of galaxies has helped us understand the natures of active galaxies, which were once big mysteries. In the late 1950s, around the time I was born, astronomers detected galaxies emitting more than just the combined light of their stars and emission nebulae. Even stranger, they were finding things that were bright, and just looked like points, as a star does â€" except that their light was not star light. They called these quasi-stellar objects, or QSOs. Eventually the awkward phrase QUASi-stellAR object was shortened to quasar. Since the prefix "quasi-" is pronounced "KWAHsee", the term "quasar" is properly pronounced "KWAHsar", not "KWAYzar", as is so common. For several decades this zoo of strange objects proliferated: radio galaxies that had broadband radio emission similar to that coming from the particle physics devices know as synchrotrons that accelerate particles to very high speeds; radio lobe galaxies that looked like ordinary galaxies in visible light photos, but that had lobes of radio emission on either side; Seyfert galaxies that looked like ordinary spirals, but that had extraordinarily bright cores; the aforementioned quasars; and blazars, that were like quasars on steroids. A decade ago, the textbook for this course dedicated an entire chapter to this zoo. (And don't worry, I'm not going to ask you about the specifics of any of the members of this zoo.) Now we've figured out that these are all the same thing. Think of water going down your drain in the bathtub. It doesn't head straight in; the turbulence of small eddies in the water ensures that it spirals inward in a whirlpool. Now think of that supermassive black hole sitting in the middle of a young galaxy. Stars and gas clouds orbit within the galaxy, taking maybe a hundred million years to complete one orbit. A few (not many, but enough) have orbits that intersect the central supermassive black hole. Many more will come close enough to it to be ripped to shreds. So over the next few hundred million years, that black hole is a glutton, swallowing up lots of material. But back to the bathtub analogy, the material forms a spiraling accretion disk (Remember that term?) around the black hole. Some of it gets swallowed up. But some of it, especially the stuff that comes in at an angle to the plane of the accretion disks, gets spun up to very high speeds, appreciable fractions of the speed of light, then spat out along the black hole's rotation axis in two jets, one in each direction, bipolar jets. (Remember those?) Two factors create the differences between the members of the zoo; the activity level of the jets, and our viewing angle. Let's say it's early in that galaxy's history, so the black hole is swallowing up lots of stuff, and the jets are ginormous and bright; as a matter of fact, they extend out farther than the galaxy is wide. To see a galaxy that early in the universe's history, I'm looking far out from Earth, so the galaxy is small and faint, so faint I don't even see it, just the jet. If I'm face-on to the jet, it's super bright, and that's what a blazar turned out to be. If I'm viewing the thing at an angle, I still can't see the galaxy, and the jet is too far away for me to resolve â€" it's just a point; that's a quasar. At some intermediate distance and age, I can see both the host galaxy and the jets, but most of the material with an orbit that intersected the black hole has already been swallowed, so the jets are weaker. Edge-on I have a radio-lobe galaxy, if face-on it's a Seyfert. For the nearby oldest galaxies, the jets are even weaker. If I notice them at all, I perceive a radio galaxy or a weak Seyfert. The artist's rendition below shows a supermassive black hole, with an accretion disk and bipolar jets. HUBBLE LEMATRE LAW Vesto Slipher: discovered that the light from virtually all galaxies is red-shifted; redshifted means:they are going away from us. Einstein's general relativity equations published in 1915 and 1917 are quite difficult to solve, with many possible solutions. Einstein said: we can't understand general relativity because it is outside the realm of human experience. We can only do the math and then check to see if what the math tells us matches the universe. TRUE The same is true for quantum mechanics. Einstein came up with an solution, but it described an expanding universe. Einstein assumed the universe was static, so he added an arbitrary constant to make the solution come out that way, an act he later called his "biggest mistake". In 1922 Alexander Friedmann published a solution that showed that the universe could be expanding. As physicists, both he and Einstein were unaware of the astronomer Slipher's work. In 1927, Belgian priest and astronomer Georges Lemaître published a solution that showed not just that the universe could be expanding, but that it is. He knew of Slipher's work and cited it as evidence. By this time Hubble had measured and published distances to many nearby galaxies that included the ones Slipher had studied. In his paper on the expanding universe, Lemaître cited Slipher's redshifts and Hubble's distances, derived the relationship that we call Hubble's law, and calculated the value of the constant we call Hubble's constant. He also pointed out that this implied a hot, dense beginning for the universe; in other words, he came up with the idea of the Big Bang. He published in French, in the journal of the science academy of the city of Brussels, Belgium. Physicists like Einstein and Friedmann knew of his work; most astronomers did not. The following year, Hubble and Lemaître met at a conference and discussed Lemaitre's ideas. Hubble came back very excited, made new red shift measurements, and in 1929 published his own paper in the prestigious journal Nature. He cited Slipher measurements, but not Lemaître's work. The paper was widely read, the relationship became known as Hubble's Law, and Hubble was credited with having discovered that the universe was expanding. (Hubble was always a consummate self-publicist â€" he even hired a publicist.) As a Jesuit-trained priest, Lemaître did what he felt his profession of faith called him to do. When Einstein urged him to translate his paper into English, he included his general relativity solutions that showed the universe is expanding, but simply omitted any reference to the astronomical evidence, or the equation now known as Hubble's law, arguing that there was no point in publishing something the world already knew, saying, "I did not find it advisable." Einstein was always quick to credit Lemaître, but Hubble is the only astronomer I know of who hired his own professional publicist. It wasn't until 2018 that Hubble's law was officially renamed the Hubble-Lemaître law, after your textbook went to press. In 1931, Lemaître published further work showing that the expansion of the universe is accelerating â€" in other words, he predicted what we now call "dark energy". This was virtually ignored until observations in the 1990s confirmed it. The photograph below is the Hubble Extreme Deep Field image. The "Hubble" here refers to the Hubble Space Telescope, named in memory of Edwin Hubble. Astronomers wanted to explore the distant reaches of the universe by pointing the Hubble telescope at a few seemingly-empty spots in the sky and taking really long time-exposures. It's about 23 days worth of exposure time of a patch of sky about 1/30th of the width of your little fingernail at arm's length (2.3 by 2 arcminutes). That exposure time is long enough to detect galaxies out to the edge of the observable universe. I've noticed only two stars in the image; pretty much everything else is a distant galaxy. In an image like this you can see the redshift caused by the expansion of the universe, astronomers call it the cosmological redshift. Notice that the nearby galaxies that look larger are either bluish (spirals), orange-ish (ellipticals), or overexposed white. But notice the scattering of small, deep-red ones, out near the edge of the observable universe, near the beginning of time. It's the cosmological red-shift that makes them look red. By the way, it's by counting the galaxies in these photographs, and multiplying that total by the ratio of the area of the whole sky to the area in the photographs, that we come up with our estimates for the number of galaxies in the observable universe.

chapter 20,21,22 BARRED SPIRALS Barred spiral galaxies resemble spiral galaxies except that their central bulges are elongated into an oval shape. Their arms go straight out from the ends of the ovals before turning sharply and taking on spiral shapes. They are designated SB, and are subdivided into SBa through SBd, with similar meanings to the spiral subdivisions. Like the spirals, they have lots of gas and dust, and lots of new star formation, making them bluish in colour. Our own Milky Way galaxy is now known to be a barred spiral, with a relatively small central bar, and is classed SBbc. The photo below is of the barred spiral galaxy NGC 1300. (galaxy that looks like a backward S) ELLIPTICALS Elliptical galaxies have no internal structure. They have little or no gas and dust, and so, no active star formation. With no new stars being formed, their short-lived O- and B-type stars are all gone, so they are yellowish in colour. They are designated with the letter E, and subdivided into E0 through E7, with E0 being more round, and E7 more elongated. The subdivisions may be relatively meaningless, since an E7 seen face-on would be called an E0. Ellipticals come in a wider range of sizes than spirals or barred spirals, the giant elliptical galaxies are several times larger than the largest spirals. (bright yellow frisbie) IRREGULARS Irregulars are, as their name implies, irregular in shape. They are small, and have no internal structure. They often contain large amounts of gas and dust, and so have ongoing star formation, giving them a bluish colour. (purple blob gas)The Magellanic Clouds pictured above are satellite galaxies orbiting our own Milky Way galaxy, and are easily visible to the naked eye from the southern hemisphere, as seen in the photo below by Hernán Stockebrand of the European Southern Observatory. GALAXY CLUSTER Galaxies are not often found in isolation. The majority of them are found in galaxy clusters consisting of hundreds to thousands of galaxies. But while stars must form in star clusters, that's not true for galaxies. Many if not most galaxies formed separately, and then were drawn by their mutual gravitation into clusters. Our Local Group is part of the Virgo Cluster of about 1,500 galaxies, which in turn is part of the Virgo Supercluster. The photo below is of the galaxy cluster Abell 2151. (looks like milky way purple/orange) GALAXY EVOLUTION**** So, here's a quick summary of what we know so far. The Big Bang produced hydrogen and helium gas (and possibly dark matter). The sound waves from the Big Bang caused matter to clump, each clump destined to become a galaxy. By a 0.2 to 0.3 billion years after the Big Bang (recall from Chapter 1 that the universe is 13.8 billion years old), stars were forming in the first galaxies. Recall also from Chapter 1 that the farther out we look in space, the further back we are seeing in time. (Be sure you understand why this is true and be able to explain it.) We find that as we look farther out, the percentages of different galaxy types changes. The earliest galaxies were small spirals (with or without spiral arms) and irregulars. As time went on, they would merge and become larger, and as their gravity increased, merger speeds would become higher. Recall that nebulae are millions of times larger than stars. When two galaxies collide, the stars almost always miss each other, but the nebulae are much larger, so are more likely to hit each other. At slow speeds, nebulae may merge, but at higher speeds the collision of two nebulae compresses them and produces a starburst, a sudden wave of star formation. Since the collision also disrupts the aligned orbits of stars in the disk of spiral galaxies, the result is a larger galaxy with its gas used up, and no internal structure left, an elliptical. The largest of these so far are today's giant ellipticals. What role did dark matter play in this story? We'd like to know, since it does make up the majority of each galaxy. The most we can say right now is that computer simulations suggest that the dark matter clumped before the normal matter did, and that the gas that formed the stars that we see in the galaxies, accreted around the dark matter clumps. DISTANCE TO GALAXIES Recall that we've now met three ways to tell the distance to an astronomical object: stellar parallax, good for only the closest stars; spectroscopic parallax, good for bright stars across the galaxy; and the magnitude/luminosity relationship of delta-Cepheid variables, good for within the Local Group. What about the rest of the universe? Here we'll meet three more methods: the Tully-Fisher relationship, "standard candles" such as Type-I supernovae, and Hubble's Law. (By the way, there are many more methods we're leaving out.) TYPE -1 SN AND OTHER STANDARD CANDLES Recall from Chapter 15 the inverse-square law, which says that brightness changes as the inverse square of distance. So, if I know how bright something is, I can compare that to how bright it appears and determine its distance. Just as the original laboratory standard for brightness was a "standard candle" of pure spermaceti weighing 1/6 of a pound and burning at a rate of 120 grains per hour, so astronomers today use the phrase "standard candle" to refer to an astronomical object of known brightness, so that if one is seen in a distant galaxy, it can be used to determine the distance to that galaxy. Type-I supernovae are used as such. Recall from Chapters 17 and 18 that Type II SN result from the implosion/explosion of high-mass stars, while Type-I SN are the carbon-detonation supernovae of white dwarfs. Type II supernovae don't make good standard candles because their brightness depends on the mass of the parent star, but Type-I supernovae are all pretty much the same brightness. Of course, there's an obvious problem; how do I know how bright a Type-I supernova is, since supernovae are rare, and there hasn't been one in our galaxy in modern times? The answer is that there have been a few in nearby galaxies whose distance is known through the delta-Cepheid variable method, so their brightness has been calibrated. Other less-reliable standard candles include planetary nebulae, emission nebulae, globular clusters, and novae. THE TULLY_FISHER RELATIONSHIP Brent Tully and Richard Fisher says: there's a relationship between the luminosity of a spiral galaxy and its rotation rate. -the rotation rate can be calculated from the spectral line width due to the Doppler effect, - if I can get a spectrum of a distant galaxy, I can read find its rotation rate on the y-axis of the graph below, then read its luminosity off the x-axis, and then compare that to its apparent brightness to get its distance via the inverse square law. THE HUBBLE_LEMATRE LAW Hubble's law: Hubble did not discover, - is a way to measure the distance to a distant galaxy from its redshift, The hubble constant-the distance is equal to that galaxy's redshift (a measure of its speed of recession) divided by a constant THE EXPANSION OF THE UNIVERSE< THE BIG BANG< AND DARK ENERGY The universe is expanding. As Lemaître said the universe is expanding means that in the past, things in the universe were closer together. He argued that Einstein's general relativity equations, which link time and space, show that time and space had to have a beginning, and that near that beginning, the matter in the universe must have been extremely compressed. Since compression heats matter, the universe also must have been really hot. Today we call this idea the Big Bang, a name Fred Hoyle gave it in derision in the '50s when he was trying to argue for a now-defunct competing hypothesis. More on the Big Bang in the next chapter. For now, let's talk about what the expansion can tell us about the future. We know the universe is expanding. We also know that gravity attracts all matter to all other matter, and must be opposing the expansion. So, the obvious question was, which would win? There seemed to be two likely possibilities. Either there's enough matter in the universe that gravity will win, eventually reversing the expansion and bringing everything back together again, an idea dubbed the Big Crunch. Or there's not enough matter to stop the expansion; the universe will keep expanding, slower and slower due to gravity, but never quite stopping. There was theoretically a third possibility, that there is exactly enough matter to stop the expansion, but not enough to reverse it. That seemed ridiculously unlikely â€" one electron too many, and the expansion would reverse; one too few, and it would continue forever. The problem was that throughout the '60s and '70s and '80s, as telescopes and measurements kept improving how accurately we knew the Hubble- Lemaître constant, its value remained very near that knife-edge case. But by the '90s, telescopes got good enough to answer the question, and the answer shocked everyone who hadn't read (or believed) Lemaître's all-but forgotten 1931 paper â€" the expansion is actually speeding up, getting faster and faster! What was causing that? Since gravity must be fighting against the expansion, many people argued there must be some unknown effect causing the acceleration. In 1998 Michael Turner coined the term "dark energy" for the effect, in reference to the term "dark matter". Many astronomers and physicists objected to the term since whatever the effect is, it's almost certainly NOT some unknown form of energy. But the name caught on. One possible explanation is that the brightness of Type-I supernovae has varied over the 13.7-billion-year history of the universe, which could mean that the expansion isn't speeding up after all. Or perhaps Lemaître's 1931 paper is right after all, and the acceleration is simply a property of space/time itself, as predicted by his solution to Einstein's general relativity equations. After all, Lemaître has a pretty good track record. If you're lucky, maybe you'll live long enough to hear the answer. Or maybe you'll become an astronomer, or a physicist, and be the one to figure it out! If you do, be sure to let me know.

LIFE IN THE UNIVERSE the origin of life. There are two possibilities: (1) Life is unique to the Earth (2) Life is common in the Universe Earth would be the only place in a Universe containing 100's of billions of galaxies with 100's of billions of stars each, many of which should have planets. -Earth or humanity is not special -Earth is not the center of the universe. -The sun is not at the center -our galaxy is not at the center and is not the largest. Later we believed that our galaxy was at the center and the largest. This was wrong too. It seems a bit anthropocentric to believe we are the only planet with life in the Universe. ---- The flip side of this argument suggests that life will occur wherever conditions permit it to occur. This leads to the difficult question of: Where is everybody else? Biologists now believe they have a good understanding of the chemical evolution of life. They had first to demonstrate that the basis of life could come from common chemical reactions. In 1953, Harold Urey and Stanley Miller conducted a very basic experiment. -In a closed environment, they generated a mixture of the gases they believed were in the early atmosphere of the Earth. -The mixture consisted of ammonia, methane, carbon dioxide and water vapor. -A continuous electric arc was produced in the mixture to simulate lightning in the early earth's atmosphere. -After a few days, a reddish goo appeared to coat most of the interior of the vessel. -An analysis of this goo showed that it consisted of a mixture of amino acids. -Amino acids are the basis of proteins which are the basis of life on Earth. Today we know that the Earth's early atmosphere was different than that in the original Miller-Urey experiment. But the early environment still supported the chemical reactions necessary to produce the precursors of life. precursers of life: amino acids, simple sugars, and the bases found in DNA and RNA are found in meteorites, so they were delivered already-formed to the early Earth. We now have evidence that: -the first very simple self-replicating molecular structures appeared within the first million years after the crust solidified and the oceans condensed, at roughly 4 billion years ago. -It took roughly a hundred million years for single-celled life to appear. -within the last billion years: single-celled critters evolved into multi-celled life and eventually the great diversity of life we have today. This all implies that life is common in the Universe. So, why have we not discovered evidence of civilizations? Astronomer Frank Drake asked this same question *Frank Drake: developed a formula to investigate the various quantities that could influence our ability to detect other civilizations. For the sake of this analysis we will assume a technological civilization is one that is using radio for communication as this appears to be the most likely way we can detect another civilization. The Drake Equation is: N = R* x fp x np x fh x fl x fi x fc x L N= is the current number of communicating technological civilizations. R* is the average rate of star formation. This is one of the easier quantities to determine. The value is about 10 stars per year. This would lead us to expect that civilizations could form at up to 10 per year. The other factors then reduce this to a more realistic level since not all stars will have planets with civilizations. fp is the fraction of the stars that form that also have planets. We now believe that planet formation is a natural consequence of star formation and this fraction has a value near 1. np is the average number of planets circling a star that would be suitable for life. There are two aspects of this quantity. Not all stars that have planets would have worlds suitable for life. Very massive stars are very hot and produce tremendous quantities of UV energy that would break up complex molecule. In addition, these stars have very short life spans that would not allow enough time for evolution to produce complex life. And just because a star is suitable doesn't mean that all its worlds are. In our own solar system, Earth has life, but what about Europa, or Enceladus, or Mars? If the average is one suitable world per star, then this factor has a value of about 0.1. fl is the fraction of habitable planets where life actually occurs. Optimists believe that if life is possible, it will occur. Pessimists believe that complex life is a very rare and unusual phenomenon. There is no general agreement on what the value of this factor could be. The range could be anywhere from 1 to 10-9 (one in a billion). fi is a factor that recognizes that just because life occurs, intelligence does not have to occur. If intelligence is truly a survival factor, then intelligence should occur and proliferate. How much of a survival factor intelligence is is debated. We cannot even agree on the number of intelligent species on our own planet, although the current definition of intelligence places the number at three. Again optimists will assume this factor to be near 1. Pessimists will assume a much smaller value. Just because intelligence occurs, does not necessarily mean a communicating technological civilization will occur. fc expresses that fraction of planets where intelligence has occurred that a civilization arises. It has been argued that cetaceans (whales and dolphins) are comparable in intelligence to humans. Because they live in water, they will never develop technologies (such as metallurgy) that would enable the creation of radio communication abilities. While this is likely to be a significant factor, we have no way to estimate its value at this time. The final factor, L, is the average life span of a communicating civilization. We know that the average lifetime of a species on Earth is about 10 million years. The human species is younger than that. Of course, we haven't been capable of interstellar radio communications for most of our existence. As a civilization, we have been emitting artificial radio waves for about 100 years (since Marconi). During the Cold War many people feared that our lifetime as a radio-communicating species would be about a century. The assumption here was that the development of nuclear energy would follow close behind the development of radio and a civilization would destroy itself. A more optimistic view says that any civilization that can find solution to the proliferation of nuclear weapons could last millions of years. *most pessimistic estimates for the factors in the Drake Equation suggest that less than a dozen civilizations exist in a galaxy at any time. Because of the size of a galaxy, these civilizations would be hundreds of thousands of light years apart. Communication would be virtually impossible. *More optimistic estimates suggest millions of civilizations among the several hundred billion stars in the galaxy. The average distances would be tens of light years and communication would be much easier. You must keep in mind the long time scales involved in the Universe. It took us, after many diversions and accidents, nearly 4.5 billion years to develop a communicating civilization that has been around for only one century. If there were a civilization developing on a planet around a nearby star, if they were only 100 years behind us, they are not ready yet. If we do detect another civilization, it is likely to be much in advance of us, possibly by millions of years. It is even possible that in the next century, we will find a much more efficient means of communication and stop using radio. If this were typical, it would not be surprising that we have found no one else. There have been several systematic searches for other civilizations that are referred to generally as SETI (Search for ExtraTerrestrial Intelligence). The last government supported project (NASA SETI) was ended several years ago when Senator Richard Bryan (D, NV) led the cancellation of the project just as it was beginning to show some promising results. NASA donated the equipment that was developed to several private, non-profit organizations (such as The Planetary Society) to carry on the work using private donations. One of the more promising projects to develop is SERENDIP run by the University of California, Berkeley. They have developed a radio receiver that listens to nearly 1 billion different frequencies simultaneously using the 1000 foot radio telescope at Arecibo, Puerto Rico. Generating over 25 Gigabytes of data per day, it will be a while before the data can be analyzed to a point that will provide results. You can help by using a free screen saver that will analyze data in free moments on your computer; available at: http://setiathome.ssl.berkeley.edu /. SETI is the search for extraterrestrial life, but there is also an academic discipline devoted to the study of extraterrestrial life; it's called astrobiology. Astrobiology folk study how life might have started here on Earth, where else might such life start, how might life elsewhere be different from life on Earth, how we might be able to detect microbial life on other worlds, and lots of other fascinating topics. One of the best web pages I know on the topic is the astrobiology web page at the University of Washington. On their website you can find a link to NASA's astrobiology page, which is also good. And be sure to check out the other astrobiology links on the Useful Links page here.

chapter 24

formula for cercumference

2 x pi x radius

Helix Nebula

Looks like eye of God

The universe is expanding: means more compressed and hotter in the past. our telescopes reveal the formation of galaxies, and then of stars; they weren't always here. early universe: filled with hot gas, expanding and cooling. back far enough: it's so hot that the atoms are completely ionized, so there's no gas, just a plasma farther back in time: it was hot enough that atomic nuclei couldn't stay together. PARTICLES AND FORCES *the twelve fundamental particles *the four forces *the categories of particles; -fermions, -bosons, -leptons, -hadrons, -baryons, -mesons, "Particles of the Standard Model". FORCES AND THEIR CARRIER PARTICLES there are 4 of them It's pretty obvious that the force that makes a spark when I shuffle my feet on a carpet on a cold winter day and then touch you, is the same force that makes lightning in a thunderstorm, but it wasn't so obvious that the force I feel when I drop a book on my foot is the same thing. *Any physical pressure you've felt is really just the electric charge on the electrons in your body being repelled by the electric charge on the electrons in the thing pushing on you. All three of these examples, as well as the attraction and repulsion of magnets, are now known as the 1. electromagnetic force. 2. gravitational force is another of the four fundamental forces. *similar electrical charges repel each other, and opposite electric charges attract; that's what keep electrons in orbit around the atomic nucleus when Newton's first law of motion says they should go flying off in a straight line. The only electrically-charged particles in an atomic nucleus are positively-charged protons, which repel each other. So why doesn't an atomic nucleus fly apart? Because there's a stronger force acting between the protons and neutrons in it. 3. This strong force in the nucleus is called the strong nuclear force. the first reaction of the proton-proton chain, a proton in a nucleus was changed into a neutron, with the production of a positron and a neutrino? It's this fourth force that did that. It's not as strong as the strong nuclear force, so guess what they called it? 4. That's right, the weak nuclear force. It's why we have sunlight, and may well be why there is matter in the universe. Unification: in the universe these four forces behave separately, but at high energies different ones start to behave identically. By the early 1980s, particle accelerators reached sufficient energies that we saw electromagnetism unified with the weak nuclear force, a unification predicted by the electroweak theory. The mathematical grand unification theory (GUT) predicts: that at even higher energies, the strong nuclear force will become identical to the electroweak force. Our particle accelerators aren't there yet, but many predictions about particle behaviour and cosmological observations shortly after the Big Bang support the grand unification theory. The standard model: Together the set of differential equations that describes this. -It predicts the existence and properties of many particles, all of which have been found, and found to have precisely the properties predicted. -It also explains and correctly predicts the properties of the three forces it incorporates. We hope that eventually we shall be able to understand gravity, and that it can be unified with the other forces. Such a hoped-for theory of everything is called the Theory of Everything (TOE). Forces are carried by one or more particles. Photon (aka light) the carrier particle for the electromagnetic force, The strong nuclear force is carried by eight different particles called gluons. (Because they glue the nucleus together) The weak nuclear force is carried by three particles called the W+, W-, and Z0. What about gravity? We're not sure yet. We presume it has a carrier particle too, and we've even coined a name for it; the graviton. But so far, we haven't detected a graviton. Gravity is MUCH weaker than the other forces1, which makes its carrier particle really hard to detect. THE PARTICLES THAT MAKE UP MATTER molecules and atoms: are composite particles â€" they are made up of smaller particles. Others, as far as we know, are not; they are indivisible, fundamental or elementary particles. Electrons, neutrinos, and quarks are all fundamental particles. You likely remember that each fundamental particle has eight properties. If you remember what they are, great, but the only ones we shall talk about here are mass, spin, and electric charge. You may also remember colour if you have read much about quarks and gluons, and you'll see flavour listed on the chart, but we'll mostly ignore those. The electron has two cousins, *the muon and the tauon. -All the properties of the electron, muon, and tauon are the same except for the masses; *the muon is about 207 times more massive than the electron, *the tauon is almost 3,500 times the electron's mass. Tauons and muons are short-lived, and decay into other particles, producing electrons in the process. three particles is associated with a different type of neutrino; -electron neutrino -muon neutrino -tauon neutrino. The neutrinos given off in the two hydrogen fusion chains in stars are electron neutrinos, and the fact that electron neutrinos interconvert into the other two flavours on their way from the Sun to the Earth turned out to be the solution to the Solar Neutrino Problem. neutrinos are produced inside your body by the decay of radioactive potassium. Protons and neutrons are composite, not fundamental; they are made up of quarks. There are six flavours of quarks; -up -down -charm -strange -top -bottom quarks2. The proton is composed of two up quarks and a down quark, the neutron is composed of one up and two down quarks. The other four flavours of quarks are short-lived, and decay into other particles, producing up and down quarks in the process. So those are the fundamental particles. Twelve that can make up matter; the six quarks, the electron and its two heavier cousins, and the neutrinos associated with each of those three. Today in the universe, all stable normal matter is made up of up and down quarks (in the form of neutrons and protons) and electrons. Then there are the carrier particles for the four forces. That's it. (Except for the Higgs; we'll get to that later.) THE EARLY UNIVERSE We don't know what caused the Big Bang. Science has not been able to answer that question; you'll have to turn to philosophy or theology for proposed answers to that. Not that scientists don't have plenty of S.W.A.G.s on the topic, just that we have no evidence. MISCONCEPTION ABOUT THE BIG BANG Sometimes people ask, "What came before the Big Bang?" It's a meaningless question, not because we don't know the answer, but because the question makes no sense, because time did not exist before the Big Bang. Speaking of "before the Big Bang" is as nonsensical as speaking of "north of the North Pole" â€" there simply is no such thing! Big Bang happened at one point, one place; that the universe started at one spot, and expanded outward. No NOT TRUE There is no "central point" to the universe. The universe is not only infinite in size now, it was infinite in size at the moment it came into existence. Some people have trouble with the concept of how an infinity can expand because they think infinity is the largest possible size. Nope. For example, the number of integers is infinite; the list goes on forever. But the number of real numbers (the list that includes irrational numbers like Pi), is larger than the number of integers. There are different levels of infinity. (If you want to know more, try any popular book about Georg Cantor's work on levels of infinity. Beware though; thinking about these drove Cantor mad.) So yes, an infinite universe can still expand. SO, WHAT HAPPENED IN THE EARLY UNIVERSE? some 10-43 seconds after the Big Bang, the electromagnetic force and the weak nuclear force had not yet begun to act separately from the strong nuclear force; they were all unified into the Grand Unification Theory (GUT). We call this era the GUT era. Before the GUT era, we presume that gravity was unified with the GUT, but until we have a theoretical understanding of why gravity exists and how it works, not just a description of its effects, we won't know. During the GUT era, all the fermions behaved the same, and no particles lasted very long. Remember pair production, by which a high-energy photon becomes a particle and an antiparticle? And annihilation, by which a particle and its antiparticle become high-energy photons? Those were both happening rapidly and simultaneously, in equilibrium, so the universe was just a turbulent soup of short-live fermions and bosons. *By 10-38 seconds the universe had cooled to the point where the strong and electroweak forces started to behave separately. (The physics jargon here is that the symmetry between the two forces had broken.) -This begins the electroweak era- -During this time quarks behaved differently than the leptons, but both leptons and quarks were still in rapid equilibrium with bosons. *By 10-10 seconds the electromagnetic and the weak force had separated, and the temperature had fallen to the point where quarks could combine to form protons and neutrons. So, pair production was now creating (and annihilation destroying) not just elementary particles, but protons and neutrons; the universe at this point was a seething hot sea consisting mostly of photons, electrons, neutrinos, protons, and neutrons. -This era is called the particle era.- So, all the familiar players are here, but it's still to hot for atomic nuclei to exist. *By 0.001 seconds, a thousandth of a second after the Big Bang, the universe -entered the era of nucleosynthesis- Remember those hydrogen fusion reactions that happen in the cores of stars? The universe was still hot enough at this point that the entire universe acted as one big stellar core. Throughout this era, protons and neutrons could fuse, only to be demolished by high-energy photons. By the end of the era, the photon energy had dropped enough to allow 2H, 3H, 3He, and 4He to continue to exist. By the time the universe was about five minutes old, -it entered the era of nuclei- when the universe consisted of H and He nuclei, electrons, neutrinos, and photons. Conditions would have been similar to those in the radiative transfer zone of our sun today. At about 380,000 years, the universe cooled to the point where electrons could orbit atoms, and -the era of atoms began.- It's during this period that the universe cooled to the point where the gas in it stopped emitting visible light, so the universe would have been transparent and dark. That leads to another name for this era, the Dark Ages Imagine floating in space, with no visible light left anywhere in the universe. By about a billion years after the Big Bang, the gas had clumped into galaxies. Our book calls this -the age of galaxies- , but I think it's more useful to talk about --the age of stars- as many astronomers do. Light returned to the universe, massive stars started producing and spewing out heavy elements, so things like dust, rocky planets, and life formed. This is the era we're in now.

S4,22, and 23 The Big Bang PARTICLES CLASSIFICATION So what's with all the strange category names; bosons, fermions, leptons, quarks, hadrons, baryons, and mesons? All these different particles, and many more, can be made by high-energy collisions in particle accelerators. physicists at the time spoke of the particle zoo. So naturally they started to explore ways to classify them; asking which properties would lead to groupings for which the members of the group also had other things in common. The classification schemes were heavily influenced by algebra and Buddhism, and many of the names were based on Greek, following the examples of proton (first one), electron (electric one), neutron (neutral one). One early attempt was to divide them into light, medium, and heavy particles; -leptons "small ones", -mesons "middle ones" -baryons "heavy ones". the amount of spin3 it has dictates some of the ways it overlaps with other particles -in particular, whether they can occupy the same space or not. Particles of light can pass through other particles of light, but electrons or quarks can't â€" they bounce off each other. Think of you and your friend; you can't both stand in the same spot, but maybe two ghosts could. The rule is that particles with integer spins (0, 1, 2, ...) can occupy the same space, but particles with half-integer spins (1/2, 3/2, 5/2, ...) cannot. Enrico Fermi: figured out the half-integer case Satyendra Nath Bose: deciphered the integer case so the two classifications of particles are named Fermions and Bosons in their honour. As you see in the chart, the force-carrying particles are all bosons, while the matter-constituents like electron and quarks are all fermions. FERMIONS There are two classes of them; -leptons -quarks. Murray Gell-Mann: predicted the existence of quarks, got the name from James Joyce's novel Finnegan's Wake Danish chemist Christian Moller: came up with the name lepton, suggesting it to physicist Leon Rosenfeld who first used it in his 1948 book Nuclear Forces. *At the time the only known leptons were less massive than the proton. A lepton (from Greek leptos, "small") was a pre-Euro unit of Greek currency so small that they never actually issued lepton coins, just used it in calculations of taxes and interest. the hadrons (Greek "bulky ones", from hadros), composite particles made of quarks. There are two sorts you're likely to run into. -Baryons (baryos, "heavy") like the proton and neutron are fermionic hadrons made of three quarks each. -Mesons (mesos, "middle") are bosonic hadrons made of quarks paired with their antimatter equivalent. They don't last long, but they are important components in the cosmic rays that contribute to our cancer risk. THE HIGGS BOSTON We mentioned the four fundamental forces. The three that we understand (we don't really understand gravity) each have carrier bosons associated with them. Not every boson is a carrier boson; -mesons are an example of bosons that don't carry their own unique fundamental forces. Forces are associated with fields. You've heard of electromagnetic fields. An electrically-charged particle, or a magnet, is surrounded by an electromagnetic field, and other charged or magnetic particles will feel that field as either an attraction or repulsion â€" the electromagnetic force. There's another fundamental boson we haven't mentioned yet, the Higgs boson, named after physicist Peter Higgs. (It's not on the chart because its discovery postdates the creation of the chart.) It is surrounded by a field called the Higgs field. -The Higgs field does not generate a force. -Instead, it supplies mass to fundamental particles. (But not to composite particles. More on that in just a moment.) How does it do that? Think of Newton's Second Law of Motion, F = ma. Rearranging for m gives m = F/a; mass = force divided by acceleration. *In other words, mass can be thought of as a resistance to motion. -Push on a small mass, it moves easily; push on a large mass, it's harder to move it. The Higgs field is what provides that resistance to motion, and we call that resistance mass; more resistance to motion â€" more mass. A common analogy goes like this. Let's say there's a crowded room at a party. I come into the room, and walk across the room to the buffet. I'm just an astronomy professor; few people want to interact with me, so I cross the room without much resistance. According to Google, the most popular actress at the time of this writing is Emma Watson. If she came into the room, everybody would crowd around her, slowing her down. I'd get to the buffet first. Of course, in the analogy, the crowd is the Higgs field, with Emma Watson and I as particles, and popularity as mass. As for the masses of protons and neutrons, most of it comes from a different source. The protons and neutrons are composed of quarks that get their masses from the Higgs field, -but the combined masses of the three quarks in each is only a tiny fraction of the masses of the proton and neutron. The quarks are moving at nearly the speed of light, so it takes a tremendous amount of energy for the strong nuclear force to hold them in their protons and neutrons. That energy is called "binding energy". Einstein's special theory of relativity says that energy and mass are two ways of experiencing the same thing, just as Maxwell showed that electricity and magnetism are two ways of experiencing the same thing. Einstein's famous equation E = mc2 can be rearranged as m = E/c2, and the masses of protons and neutrons (and hence of us) comes from plugging the tremendous binding energy of quarks into that equation. We would not have most of our mass without special relativity THE FUTURE We know that stars are turning hydrogen to helium. Eventually the hydrogen will run out, and shortly after that, the stars will stop. And we know that the expansion is speeding up. First, other galaxy clusters will move out of our observable universe. Then other galaxies. Then other stars. Of course, we won't be here to see it. By 8 billion years into the future our sun will become a red giant, engulfing and vaporizing the Earth. Our sun's light output is slowly increasing, so within half a billion years, it will be too hot for multicelled life on Earth. All life will be microorganisms hanging on in the deep subsurface. By about 2 billion years when the oceans boil away, Earth will be a lifeless ball of hot rock. If we want to still be around, we're gonna need a space program! SUPPORTING EVIDENCE There are more than a dozen types of evidence for the Big Bang, but let's stick to the three our book mentions. *The early universe was hot enough to glow. That light is still around, but the expansion of the universe has stretched its wavelengths out into the microwave range. We call it the cosmic microwave background (CMB). It's direct evidence for the Big Bang, and the details of it have a great deal to tell us about the history of the early universe we've just discussed. *A second strong piece of evidence consists of the relative abundances of 1H and 2H, and of 3He and 4He. Even slight changes in the era of nucleosynthesis would have produced different ratios of those isotopes, so they tell us a great deal about conditions in that era. *A third is Olbers' paradox. Our book's explication of Olbers' paradox in incomplete, so let's see if we can clarify it. The paradox is that if the universe is infinite and filled with an infinite number of stars, then in whatever direction we look, we should be looking at the surface of a star, so why is the night sky dark? Olbers wasn't the first person to write about it; Thomas Digges did it, then Kepler did it, and several other people, but somehow Olbers' name got attached to it. There are several possible solutions. One is that the universe isn't infinitely old, so that light from distant stars hasn't had time to reach us yet. Edgar Allen Poe even wrote about this in his 1848 essay Eureka: "Were the succession of stars endless, then the background of the sky would present us a uniform luminosity, like that displayed by the Galaxy â€" since there could be absolutely no point, in all that background, at which would not exist a star. The only mode, therefore, in which, under such a state of affairs, we could comprehend the voids which our telescopes find in innumerable directions, would be by supposing the distance of the invisible background so immense that no ray from it has yet been able to reach us at all." Did you know Poe was a science geek? After all, he invented science fiction! Anyway, that's the explanation our book mentions; that the universe is not infinitely old, so we can only see the light from the observable part of the universe. What the book fails to mention is that the Big Bang creates another problem for Olbers' paradox; the early universe was hot enough to glow, and that glow comes at us from all directions, so the night sky should not be black. Of course, we've just seen the solution to that half of the paradox; the expansion of the universe has shifted that glow into the microwave region of the spectrum. Now let's take a look at a very interesting question. Is there life anyplace else in the universe?

The Greek word "planetes" means:

Wanderer

At what time did the universe become transparent?

About a third of a million years after the Big Bang

3 stars on Orions belt

Alnitak, Alnilam, Mintaka

Flamsteed numbers ( a system created by):

John Flamsteed- an astronomer royal to the throne of England, in which each star is given a number followed by the constellation name

Copernicus' model was able to eliminate the need for equants. It also explained retrograde motion in a different way, as an illusion whenever a slower outer planet passes Earth.

Although Copernicus' model was simpler than Ptolemy's it was not more accurate; Tycho's more precise observations at the end of that century showed that similar errors existed in both models. It wasn't until Kepler introduced elliptical orbits into the heliocentric model that it finally became more accurate than Ptolemy's geocentric model. after Revolutions was published it was not initially considered a threat by the Church. However, by 1610, the Protestants were using Copernicus' work as an example of how what was taught in Church schools could be wrong, and arguing that therefore the Church's theology could be wrong too, so Revolutions was placed on the Index, the list of banned books.

If I view a typical star at the same time from the US and Japan, Which set of celestial coordinates will change?

Altitude and azimuth

-Willamina Fleming colleagues at Harvard observatory are:

Antonia Maury, Henrietta Swan Leavitt, Cecilia Payne Gaposhkin, and my favourite astronomer Annie Jump Canon

Yellowish star in the top left of Orion is:

Betelgeuse

Tycho (continued) In the picture at right, Tycho is observing with a large mural quadrant. This measuring device allowed him to get the precise altitude (to an arc minute) of a star or planet as it crossed the meridian. This gave an accurate value for the declination of the object. The time it crossed the meridian gave a value for the right ascension of the object to a similar precision. Tycho felt his observations did not support the Ptolemaic model (so he created his own model). The Tychonian System has the Earth at the center. The Moon and Sun both revolve around the Earth on circles. The planets, however, revolved around the Sun. In essence, his model was the same as Copernicus' (except that earth was stationary and everything else continued to move in the same relative manner.)

By 1597, Tycho fell out of favor with the Danish court and moved to Prague. There he hired a young Polish mathematician, Johannes Kepler, to make sense of his observations and hopefully prove his theory on the nature of the Solar System. Tycho was one of the more unusual characters in the history of astronomy. As a teenager in University, he got into a disagreement with another student. In those days disagreements were settled with swords, and Tycho lost his nose in the duel. F or the rest of his life, he wore a silver artificial nose (he had a gold nose for state occasions). As the Lord of Hveen, he so mistreated the serfs in his domain that when he left, they burned his castle and observatory to the ground. Tycho's death was even stranger. It was long said that he was attending a state dinner at the court in Prague in 1601 that resulted in his death. His rigid interpretation of protocol was that no one left the table before the king. After much drinking and dining, Brahe collapsed at the table from a burst bladder and died several days later from the infection. But it has recently been claimed that Kepler murdered Tycho and stole the famous data on planetary motion, and their is some forensic evidence to support this.

Chapters 16, 17, and 18 -These three chapters tell the story of the life cycles of stars. I know stars aren't really alive, but the temptation to anthropomorphize them is too great; we talk about stellar nurseries, star birth, stellar lifespans, star death. Forgive us, please. They mostly consist of a flowchart called the "Stellar Evolution Study Guide", as well as a bit of supplemental text here. The Study Guide is available in three versions. *primary version is the gold edition. *secondary version is the silver edition. *third is bronze (The Interstellar Medium) Stars form from clouds of gas and dust floating in interstellar space. We call such a cloud a "nebula", which is simply the Latin word for cloud; the plural is "nebulae". A typical nebula is huge, a thousand up to a million times the size of our solar system, but the gas inside is very thin, about 1015 (10 quadrillion) times less dense than the Earth's atmosphere. The gas produced by the Big Bang was about 90% hydrogen and 10% helium, but over time stars have been fusing hydrogen into helium, and helium into heavier elements, so a nebula today is about ¾ hydrogen, about ¼ helium, and about 2% everything else. Half of that "everything else" is gas, but half has condensed into dust, so dust makes up about 1% of a typical nebula. A volume of a nebula the size of a football stadium might hold a couple of dust grains. So, the gas is about ¾ hydrogen, ¼ helium, and 1% heavier gasses. What's the dust? First of all, the dust grains are tiny; about the size of the particles in cigarette smoke. The particles have an inner core of a mineral grain, usually the silicate mineral olivine but occasionally iron/nickel metal, or the silicate minerals feldspar or pyroxene. Then the mineral grain is surrounded by a mantle of an ice, a mixture of frozen water, methane, and ammonia. (Detecting the Gas) Since gas is transparent, how do we know it's there? One way is fluorescence. I'm sure you've seen black-light posters, and paints that glow under UV light. (Think EDC.) O- and B-type stars are hot enough to give off substantial amounts of UV light. When electrons in gas atoms absorb that light and move to larger orbits, they can drop back down and emit light, just as we learned when studying emission spectra. When light emission is triggered by the absorption of UV light, it's called fluorescence. The UV light will probably be absorbed before it travels completely across the nebula, so only a portion of the nebula will fluoresce. Astronomers call these emission nebulae, since they were named before it was understood that the emission was due to fluorescence. Different gasses fluoresce with different colours, but the most common colour in the universe is the red emission line in the hydrogen spectrum know as H-alpha. Recall H-alpha light as the characteristic light of our sun's chromosphere. In the photo below, the large areas glowing red are emission nebulae fluorescing with H-alpha light. (What constellation is this?) Other gasses have their characteristic colours; oxygen, for example, glows green. Suppose there is no nearby O- or B-type star? If there is a star behind the gas cloud, the passage of that star's light through the gas cloud will cause absorption lines in the star's spectrum, besides the absorption lines already there from gasses in the star's atmosphere. Since it's likely that the nebula and the background star are not moving at precisely the same velocity, the Doppler shifts of the two sets of lines will be different. And recall that pressure affects spectral line width, so the absorption lines from the nebula will be much thinner than those from the star's atmosphere. Both these methods depend on circumstance. Is there a nearby hot star to cause fluorescence? Is there a sufficiently bright background star from which we can get a spectrum? But there's one method that will detect a gas cloud even when the others fail, radio emission. Recall from our study of spectroscopy that visible light is emitted by orbital electrons moving closer to the nucleus. Radio emission spectra are produced not by electron transitions between orbits, but by electrons, atomic nuclei, or molecules changing rotation states. Hydrogen, for example, has a radio emission with a wavelength of 21 cm. Not only can we detect gas clouds by their radio emission, the emission can typically pass through dust clouds so that we can see gas clouds behind dust clouds, and radio spectroscopy can identify various molecules present in the clouds. Radio spectroscopy has now identified in nebulae many building blocks of biological systems such as all the common amino acids that make up proteins, all the common nucleic acids that make up DNA and RNA, and several of the sugars that are ubiquitous as structural components and fuels of cells. (Detecting the Dust) (extinction, reddening, reflection) How do we detect dark dust in the darkness of space? One way is that if there's a light source behind the dust, and the dust hides it; that's called extinction. Of course, the challenge is to know that there's a light source back there you can't see! In the picture of the Horsehead Nebula below, it's fairly obvious the swirl of dust in the shape of a horse's head is blocking H-alpha light from the emission nebula behind it. Sometimes in a part of the sky where stars are common, dust clouds can also be obvious due to extinction; we'll see an example of this below. Another detection method is reddening. Due to the typical size of interstellar dust grains, light passing through a dust cloud will preferentially have its blue light scattered, leaving the redder light to come straight through. Look at the picture below, near the Milky Way in the summer sky. In the top center and at left you can see extinction due to dark lanes of thick dust silhouetted against the densely-packed background stars. But along the left and bottom edges the dust is thinner, not completely blocking the light, but causing reddening. Near the center of the picture above is a triangle of stars each surrounded by a seemingly glowing region. The one surrounded by red is a case we've seen before, a hot star sitting in a gas cloud, causing H-alpha fluorescence in the nearby gas. But what about the yellow star surrounded by yellow, or the blue-white star surrounded by blue? Those are cases of reflection, another way to detect dust. All those methods depend on circumstance; a background light source or a nearby light source. But, just as gas can relaiably be detected by its radio emission, dust also has a method that allows us to detect the majority of dust clouds. Dust is dark, and will absorb starlight and warm up a bit. It's typically 10 K to 15 K warmer than the surrounding cold, dark space, which is at 2.7 K. Plug that temperature into Wien's Law, and the resulting emission is at millimeter wavelengths, long-wavelength infrared. So, to a long-wavelength infrared telescope, dust clouds glow. It's not quite as good as using radio to detect gas clouds, since dust clouds can be hidden behind other dust clouds. But, it's the best method we have. (Star Formation) Now lets turn to the Stellar Evolution Study Guide. Download it, open it, and follow along, and I'll walk you through it. At the top you see the interstellar medium listed, with most material recycled from previous generations of stars, but ultimately coming from the Big Bang. Gas in a vacuum tends to expand, so a nebula can diffuse away and dissipate. But, if the nebula is large enough, its own gravity can cause it to collapse inward and shrink to form stars. If you see a nebula today, obviously it hasn't done either one â€" it's still there. But, things can trigger the collapse, like compression from passage through a galactic spiral arm, the shock wave from a nearby supernova, or collision with another gas cloud. Gas atoms in a nebula can bump into each other and chemically bond together to form molecules, but these typically don't last long, as stray photons of UV from distant hot stars break the molecules apart again. But, as the shrinking cloud grows more dense, incoming UV gets absorbed in the outer parts of the cloud and the interior of the cloud is shielded, allowing molecules to exist. This is known as self-shielding, and the cloud is now a molecular cloud. By chance, the mass a cloud needs to have this happen is about the mass it needs to form stars, so molecular clouds (identifiable by molecular emission lines at radio wavelengths) are potential sites of star formation. Not every molecular cloud will go on to form stars; some can still diffuse and dissipate. And nebulae are not quiet, homogenous places; they are rather turbulent. [Do other nebulae ever say about them, "We walk in the garden of his turbulence"? Kudos if you know that reference!] So, the nebula gets twisted into clumps, each of which may go on to become a star. Recall from high school science class that compressing a gas heats it; that fact will be extremely important to us in these three chapters. In the stages we've discussed so far, the shrinking cloud has been able to shed heat and maintain its temperature by emitting infrared light, but as a cloud fragment contracts further, the density becomes sufficiently high that infrared radiation can no longer escape, and the cloud's internal temperature starts to rise. The inner, hot part of the cloud is now a protostar. Most protostars aren't seen with visible light telescopes because any light they emit is shrouded by the cool, dusty, outer part of the cloud fragment. But recall that infrared light can penetrate the dust, and the hot protostar is giving off plenty of that. So, if I look at a molecular cloud like the Orion Nebula, I can see compact dust clumps within it. Infrared telescopes reveal that many of those clumps harbour protostars; such a clump is known as a cocoon nebula. As a protostar heats up, convection starts in its interior, and gasses start to boil off the surface, a stellar wind analogous to our sun's solar wind. As more material spirals into the protostar, centrifugal force funnels the infalling material into an accretion disk ("to accrete" means "to come together") in the plane of the protostar's equator. This accretion disk blocks the outgoing stellar wind so that it escapes mostly along the rotation axis in two jets, one at each pole â€" bipolar jets. Eventually the stellar wind blows the surrounding dust away and the protostar is revealed. When the temperature and pressure in the protostar's core become sufficient to support the nuclear fusion of hydrogen into helium, the protostar is now a main sequence star. But not every protostar will become an MS star. If a protostar is less than 8% of the mass of the sun, it will never reach conditions to support hydrogen fusion, so even though it was glowing and looked like a star, it will soon fade. Such a failed protostar is called a brown dwarf. And surprisingly, a protostar can be too massive to become a star It was Kepler who first proposed that light exerts pressure, though it took James Clerk Maxwell to explain how radiation pressure works. If a protostar is sufficiently massive, it will generate enough light to tear itself apart before reaching the necessary conditions for hydrogen fusion. The exact mass needed for this depends on the precise amounts of heavy elements present, but if a protostar is more massive than around 150 times the mass of the sun, it will be disintegrated by its own radiation pressure, and not form a star. The critical masses at the branch points on the Study Guide flowchart are shown in green, and the characteristic colour of light given off at each stage is suggested by the colour of the boxes surrounding the labels. ------------------------------------------------------------------------------------------ (Star Life and Death) Once hydrogen fusion starts in the core of a collapsing nebular fragment, the fragment is no longer a protostar, but a star. For our purposes, we're going to divide stars into three categories; * low-mass stars with less than twice the mass of the sun, *intermediate mass stars whose masses range from twice the mass to eight to ten times the Sun's mass *high-mass stars with more than eight to ten times the sun's mass. Depending on their area of research different astronomers might put these dividing lines at different masses, or use different categories altogether, but these are pretty much the ones our book uses, and will best suit our purpose. (Low-Mass Stars) Let's start with the low-mass stars, defined for us as stars with less then twice the mass of the sun. Of course, that makes our sun a low-mass star. For a star of one solar mass, like our sun, hydrogen fusion happens when the core temperature reaches 10 million Kelvin. Critical temperatures are shown on the flowchart in purple, in units of GigaKelvin (billions of Kelvin). What defines this low-mass category is the way hydrogen fusion happens. Low-mass stars fuse hydrogen primarily via the proton-proton chain, called the pp chain. It's the set of three reactions that power the sun, so if you didn't learn them then, you'll need to be sure to learn them for this next exam. Each chemical element is defined by its number of protons; *hydrogen has one, *helium two, *lithium three, et cetera. Atoms can differ in the number of neutrons, producing different isotopes. The isotopes are written as the chemical symbol with the mass number (the number of particles in the nucleus) superscripted at the top left. *Hydrogen for example has two stable isotopes, 1H and 2H; both have a single proton, but 1H has no neutrons while 2H has one. *Isotope names are pronounced with the chemical symbol first, then the mass number; *1H is called "aitch one", 2H is called "aitch two". *Hydrogen also has a radioactive isotope, 3H, with a half-life of 12.32 years. *Half-life is the length of time it takes half of a radioactive material to decay. *After one half-life, you have half what you started with; after two half-lives, a quarter; *after three half-lives, an eighth, et cetera. *Hydrogen is the only element whose isotopes have alternate names; *2H is deuterium, and 3H is tritium. *Helium has two stable isotopes, 3He and 4He. the sun that the three main reactions of the pp chain are: 1H + 1H> 2H+ B+ v 1H + 2H > 3H + ys 3H + 3H > 4He + 1H + 1H where the symbol beta + is a positron, nu is a neutrino, and gamma is a gamma ray. There are some side reactions listed on the gold-edition flowchart, but you needn't memorise those. While any nuclear reaction is running in a star, it is in balance between two forces; gravity that wants to make it shrink, and radiation pressure that wants to make it expand. The star will be stable, and its size, brightness, core temperature and surface temperature can change only very slowly. Our sun will stay on the main-sequence, fusing hydrogen into helium via the pp chain, for about 12 billion years. Given that it's 4.54 billion years old, it has another 7.5 billion years to go as a MS star. (The Earth won't be inhabitable nearly that long, though. Within another half billion years there will be no multi-celled life on Earth.) It's important that you understand what happens to a star when a nuclear reaction in its core runs out of fuel and stops, as we'll see this happening over and over again, and it will be the driving mechanism behind the changes a star undergoes throughout its life. When the hydrogen in the sun's core is used up (it's currently about 50%), hydrogen fusion of course stops. With no nuclear reaction taking place to generate radiation pressure, the balance between radiation pressure and gravity is shifted. Gravity wins (for the moment), and the core shrinks. Recall that compressing a gas raises its temperature, so the core not only shrinks, it gets hotter. That heat soaks out to the outer layers. Recall from high school science class that heating up a gas makes it expand, so the outer layers expand and" the sun will engulf the Earth at this point. Recall also that letting a gas expand lowers its temperature, so the surface of the sun will cool from yellow-hot to red-hot; the sun will become a red giant. And yes, this means that the outer layers received more heat, but got cooler. Recall that heat and temperature are not the same thing; in this case, the heat energy didn't go to raising the temperature, it went to expanding the outer layers. We'll see this repeatedly, that when a nuclear reaction in a star's core stops, the core contracts and heats up, while the outer layers expand and cool. The core won't keep shrinking and heating up forever. Once the core temperature reaches 100 million K (0.1 GK) a new nuclear reaction starts, helium fusion via the triple-alpha process. You'll need to know these three reactions for the exam****** 4He + 4He > 8Be 4He + 8 Be > 12C + b+ B 4He + 12C > 16O + y Since this reaction happens at much higher temperatures and pressures than the pp chain, it runs faster; our sun will only stay a red giant for about 0.01 billion years. You can see on the gold edition that there are some other named phases the sun goes through at this point (horizontal branch and asymptotic giant branch stars), but this semester we'll just lump them all under red giant, as seen in the silver edition. We'll come back to the s-process later in this chapter. Low-mass stars have a problem with the triple-alpha process; it's not stable for them. Here's how that works. Helium fusion starts. More energy is produced in the core, making it expand. That makes it cool off, so the temperature drops below the minimum for helium fusion, and the triple-alpha process shuts off. Once it shuts off, there's less radiation pressure in the core, so it shrinks, which makes it heat up, which starts helium fusion again. Helium fusion thus cycles on and off, with periods of 100,000 years or so. And each time fusion starts again, more heat leaks to outer layers, which expand with each cycle. Eventually they expand out to about the distance of Neptune's orbit, where the gravity from the core can't hold them any longer, and they just keep going. The result is that the star's core is exposed, and is surrounded by an expanding shell of glowing gas. The exposed core is made of carbon at this point. It's shrunk to the size of the Earth, and is called a white dwarf. More on them in the next chapter. The gasses in the expanding outer shell are exposed to lots of high-energy radiation (UV and X-rays), causing them to fluoresce. They are visible for a few 10,000s of years or so before dissipating, and while we can see them, we call them planetary nebulae. The term is misleading; they have nothing to do with planets. William Herschel coined the term in 1790 when he was looking at NGC 1514 because it was round, and had the blue colour as the planet Uranus he had recently discovered. The gas in a planetary nebula doesn't expand evenly; nobody's sure why. Perhaps the shell is shaped by the presence of a second star in a binary system. Perhaps the outflow is restricted along the equator by dust from vaporised planets. Perhaps the flow is channeled by the star's magnetic field. Or a mixture of these. But many planetary nebulae are bipolar; then how they appear to us depends on whether we are seeing them from the side, or looking down the axis. The montage of 100 planetary nebula below, all to the same scale, was assembled from Hubble images by Judy Schmidt, better known online as geckzilla or SpaceGeck, an avid amateur astronomical image processor. (Intermediate-Mass Stars) Now let's look at intermediate-mass stars, those from two solar masses up to eight to ten solar masses. The flexibility in the upper mass range is because there's some dependence on the chemistry. If a star of nine solar masses has fewer heavy elements, it behaves as an intermediate-mass star; if it has more heavy elements, it behaves as a high-mass star. Intermediate mass stars differ from low-mass stars in two primary ways; they fuse hydrogen differently, and their helium fusion is stable. Intermediate-mass stars fuse hydrogen primarily via the CNO bicycle. The last two syllables of "bicycle" here are pronounced like the word "cycle", so the word is pronounced differently than the name of the two-wheeled conveyance. Chemists already had the concept of a "catalyst", a substance that takes part in a chemical reaction but is not used up in it, often because it's changed, and then changed back. The same thing can happen in nuclear reactions. ---- ---- ---- ---- ---- ---- In this case, carbon, nitrogen, and oxygen nuclei are catalysts in a four-step chain that fuses hydrogen to helium. The four reactions in the first cycle are: 1H + 12C > ys + 13N > 13C + B+ + v 1H + 13C > 14N + ys 1H + 14N > ys + 15O > 15N + B+ v 1H + 15N > 12C + 4He The carbon-12 produced in the last reaction feeds back into the first one, making a cycle. You'll need to know these first four reactions for the exam. As you can see in the flowchart, one out of every 2,000 times a second cycle follows this first cycle, making the whole thing a bicycle. Just as in low-mass stars, when the hydrogen is used up the core shrinks and heats up, and the outer layers expand and cool. Helium fusion will ignite in the core, but now the more massive star exerts enough pressure on the core to keep the reaction running smoothly with no pulses. The higher pressure makes the triple-alpha reaction run faster than it did in low-mass stars, swelling the star to a supergiant. Eventually, just as in low-mass stars, the star will expand to the point it loses its outer layers as a planetary nebula, exposing its core as a white dwarf made of carbon with a bit of oxygen. (High-Mass Stars) Stars greater than eight to ten solar masses also fuse hydrogen into helium via the CNO bicycle, and also then smoothly fuse He into C and O via the triple-alpha reaction, but they can reach sufficient pressures and temperatures to go on to other nuclear reactions. The products of these reactions are what you would get if you added 4He to 12C to get 16O, added 4He to that to get 20Ne, then up through Mg, Si, S, Ar, through all the even-numbered elements up through Fe. The process stops there, because adding He to Fe produces a radioactive isotope of Ni which decays back into Fe again. That's not really what happens, but the results are similar. The silver edition calls this process the serial fusion of He, and it's what you should know for the exam. But it's not what really happens. The gold edition shows what really happens. Yes, the serial fusion of He with C proceeds through O and Ne to Mg, but along with that, C nuclei are also fusing with other C nuclei to form Ne and releasing more He to help the process along. The conversion of the core to Mg and Ne takes only about a thousand years, much less time than the star spent as an MS star, or while fusing He. After that the core contracts and heats up. It's so hot now, 1.2 GK, that according to Wien's law, the core is emitting mostly -rays. The gamma rays break down some of the remaining Ne into O and He, and the He can then combine with any remaining Ne to make Mg. This takes only a few years. Now the core again contracts and heats up. Oxygen from a shell around the core can fuse to make Si and He, a reaction that takes only months. Once again the core contracts and heats up. Finally Si can undergo serial fusion with He to form Fe, which takes only a day. Things are getting hectic for this core now. Once the core is made of Fe, no more nuclear fusion reactions are possible. Radiation pressure lessens, gravity wins, and the core implodes. The iron atoms are rushing inward now at about ¼ the speed of light. As the core heats up, Wien's law ensures that it's now glowing with high-energy gamma-rays, which soon have enough energy to shatter the Fe nuclei into He nuclei and neutrons, a process known as photodisintegration. All the work that fusion has done since the triple-alpha reaction is now undone in a few seconds Fe, Ni + y > 4He + n We've been ignoring the electrons. Back when this thing was a protostar, it got hot enough to ionize the atoms, and ever since then we've just been letting the electrons mill around whilst we concentrated on the atomic nuclei. But they're still there. Now the temperatures and pressures are high enough that they can combine with the protons in the He nuclei, producing neutrons and gamma-rays. 1H + B > n + y Now this core is nothing but neutrons, heading inward at a quarter the speed of light. Soon the neutrons collide and bounce off each other â€" now they're headed outward at a quarter the speed of light (except the ones in the middle that got bounced off of). The temperature is now high enough that neutrinos are being produced by the high heat. The rebounding neutrons and the neutrinos tear the outer layers of the star apart; a supernova explosion. The neutrons in the middle, the ones that got bounced off of, are left behind as a ball of neutrons called a neutron star. More on these in the next chapter. If the resulting neutron star has less than 20 times the mass of the sun, we can see it. But if it has more than 20 times the mass of the sun, it will have sufficient gravity to hold in its own light, and we won't be able to see it directly. We call these sorts of neutron stars black holes. More on them too, in the next chapter. If you look on the gold edition, you'll see two other possible fates for very high-mass stars. If the star is more massive than 50 times the mass of the sun, the core collapse will sufficiently concentrate its gravity so that the collapsing core becomes a black hole. The rest of the star will fall onto this black hole, and no supernova will occur. As of this writing, we've seen this once. The second case is with stars over about 140 times the mass of the sun. (Recall that no star over 150 solar masses can form, so these are rare indeed!) The collapsing core can become so hot that extremely high-energy gamma rays will undergo pair production, changing into electron/positron pairs. 2ys > B+ +B- Since positrons are antimatter to electrons, they will annihilate with the next electron they hit, producing two gamma rays, the exact opposite of the pair-production reaction above. The entire star is destroyed in a pair-instability supernova, a much more energetic event than the sort of supernova we've just been discussing. We've observed just one of these, as well. (Nucleosynthesis) You may have noticed that this story goes a long way towards explaining the origin of the chemical elements. H and He nuclei were produced during the Big Bang, a process scientists call Big Bang nucleosynthesis. All the other elements are produced in stars â€" stellar nucleosynthesis. But we haven't yet explained them all. After the Big Bang, the universe was 90% H, 10% He. Hydrogen fusion happens in every star, and is turning H into He. Today the universe is about ¾ H and ¼ He. The triple-alpha reaction happens in every star, turning He into C and O, but in low-mass and intermediate-mass stars that material stays locked up in white dwarfs, so it can't be the source of the C in our bodies and the O we breathe. The carbon and oxygen in our bodies is produced in high-mass stars. The other fusion reactions in high-mass stars produce the even-numbered elements between carbon and iron, then thrown out into space when the star explodes. We've seen that. But what about the odd-numbered elements, and the elements heavier than iron? Enter the s-process and the r-process. The letters s and r stand for "slow" and "rapid". The s-process is the slow neutron capture process. (It's the capture process that's slow, not the neutrons. There are such things as slow neutrons, produced by moderation of fission neutrons in reactors, but I digress.) Go back to the red giants, technically to the asymptotic giant phase of the red giants. Carbon and oxygen are being produced by the triple- process. Some side reactions we haven't discussed are occasionally producing neutrons. What happens if I add a neutron to the nucleus of an even-numbered element? I get the next heavier isotope of that even-numbered element. Maybe it's stable, or maybe it's radioactive. But if I keep adding neutrons, eventually I'll get to a radioactive isotope of that even-numbered element. It will decay by converting a neutron to a proton, emitting an electron and a neutrino in the process, just as we saw in the first reaction of the pp chain. So that nucleus has now gained a proton â€" it's now the next element along on the periodic table, and now an odd-numbered element. That's how the odd-numbered elements get produced. This process can get past Fe, up to Sr and Y, and sometimes even up to Bi. This is why elements heavier than iron, like gold, are rare â€" they're only made by this side reaction. But there aren't that many neutrons running around in stars, so an atom might undergo the s-process once every half million years or so, working its way up as the star ages to once a decade; this reaction can't produce enough of these to account for their abundance in the universe, and can't make elements heavier than Bi. Where do those elements come form? That's where the r-process comes in. The r-process is the rapid neutron capture process. Again, it's the capture process that's rapid, although in this case the neutrons are rapid, too. Let's say there are a kajillion neutrons around, enough so that a nucleus can capture one hundreds of times a second. A nucleus captures one and becomes radioactive. But before it can decay, it captures another, and becomes a shorter-lived isotope of the same element. Soon it's captured dozens, and is an extraordinarily neutron-rich, unstable, radioactive isotope of the starting element. Now when the neutron flood ebbs, these dozens of extra neutrons all quickly change to protons, resulting in elements dozens of places farther along on the periodic table. Where do we find such a flood of neutrons? One place is during a supernova explosion, but detailed modelling showed that the mix of elements and isotopes produced there doesn't quite match what we see in the universe. There must be another place where a flood of neutrons can occur. We now believe this second source is in collisions between neutron stars. Those would be unlikely if neutron stars were just drifting around galaxies at random, but all it takes is two massive stars in a binary pair to produce an orbiting pair of neutron stars, which will then spiral into each other as they lose energy by shedding gravitational waves. (That's a subject for a sophomore-level class.) ------------------------------------------------------------------------------------------ (Corpses & Zombies) How are stars like fictional humans? Their corpses can be reanimated. First, we'll talk about the variety of stellar corpses, then about the varieties of stellar zombies. (Stellar Corpses) You've already met the three types of stellar corpses; white dwarfs, neutron stars, and back holes; we'll talk a bit about each. (White Dwarfs) Recall that white dwarfs are the corpses of low-mass (like our sun) and intermediate-mass stars. Most white dwarfs are composed mostly of carbon (though the book mentions some exceptions). Take a star the mass of the sun, and compress it down to the size of the Earth. A sugar-cube size chunk of a white dwarf would weigh about a ton, so the surface gravity is more than a hundred thousand times greater than Earth's. Take your weight, and multiply it by 100,000 â€" that's what you would weigh on a white dwarf. Of course, you wouldn't survive that; your bones would be powdered, your cells ruptured, and you would be a grease spot on the surface. Oddly enough, the more massive white dwarfs are smaller, since their greater gravity further compresses them. Another way to describe the strength of the surface gravity of a white dwarf is its escape velocity; how fast would something have to be going to escape the surface. The escape velocity of Earth is 11 km/s (25,000 mph), that of the Sun is 620 km/s (1,400,000 mph). To escape from the surface of a white dwarf, you would need to be travelling at 6,500 km/s (15,000,000 mph). (Neutron Stars) Recall that neutron stars are the corpses of high-mass stars, the remnants left behind after a supernova implosion/explosion. They are compressed to very small sizes, roughly ten miles across. Neutron stars have densities similar to those of atomic nuclei, so a teaspoon-full brought to Earth would weigh what a mountain would. The surface gravity is about 100 billion times that of Earth, so if you landed on a neutron star, not only would your cells be ruptured, the chemical bonds between your atoms would be broken, and your atomic nuclei broken down into protons and neutrons. To put it another way, the escape velocity from a neutron star is at least 100,000 km/s (220,000,000 mph). Since neutron stars are so very small, no matter how much light they give off per square inch, they just don't give off that much total light, so they are very hard to detect. But as they were compressed during formation, gravity wasn't the only property that was concentrated. They have extremely strong magnetic fields, and they spin very fast, at least once per second. Consider that a neutron star has just been at the center of a supernova explosion. It's very hot, so the stellar wind (the particles boiling off its surface) is quite strong. But the magnetic field is so strong that the charged particles boiling off the surface are funneled into two jets exiting above the magnetic poles. Since it's unlikely that the magnetic poles are aligned with the rotational poles, the neutron stars rotation sweeps these jets around like the beams from a lighthouse. The strong magnetic field also causes these jets to emit electromagnetic radiation such as light along these beams. If the beams don't happen to be pointed towards us, it's unlikely we will detect the neutron star. But if a beam sweeps across us, we'll see a flash every rotation. We call a neutron star detected this way a pulsar. The first pulsar was detected in 1967 by Cambridge graduate student from Northern Ireland Jocelyn Bell, and deciphered by her major professor Anthony Hewish. He received a Nobel prize for that, a prize many of us feel she should have shared. Jocelyn Bell (now Dame Susan Jocelyn Bell Burnell, DBE, FRS, FRSE, FRAS, FInstP) was later award the $2.3 million Special Breakthrough Prize in Fundamental Physics; she donated the entire prize to helping female, minority, and refugee students seeking to become physics researchers. Incidentally, if you're interested in the attitudes of religious scientists, I recommend her chapter, Quiet Path, Quiet Pool in the book, Spiritual Evolution: Scientists Discuss Their Beliefs in which she describes her personal and Quaker faith. (Stellar-Mass Black Holes) We mentioned that neutron stars are very compressed, and their surface gravity is so strong that their escape velocity is at least 100,000 km/s. Depending on the mass of the neutron star, it can be higher than that; 200,000 km/s, 300,000 km/s, 400,000 km/s. But nothing can go as fast as those higher numbers. Einstein's General Theory of Relativity shows that there is a maximum speed at which anything can travel through space (technically, spacetime). Light and a few other things travel at that speed, the speed of light, 300,000 km/s (670,000,000 mph). So, if nothing can travel faster than the speed of light, and if something would need to travel faster than the speed of light to escape a massive neutron star, obviously nothing is going to escape those massive neutron stars, not even their own light. Not only that; we can't even see them by reflected light, since once the light bounces off the surface, it still can only travel outward at the speed of light. We call such neutron stars black holes. Specifically, they are stellar-mass black holes, since they have roughly the mass of a star. Consider a neutron star whose escape velocity is exactly the speed of light. Nothing could escape from its surface (making it a black hole), but a bit above the surface the escape velocity would be lower, so light could escape from a bit above the surface. But now consider a more massive neutron star. The escape velocity at its surface would be above the speed of light, so nothing could escape from there, but even for something just above the surface, the escape velocity would still be greater than the speed of light, and nothing could escape. So, for any neutron star above the minimum mass to be a black hole, there's a volume of space around it from which nothing can escape. We call the outer limit of this volume the event horizon. Unfortunately, there are several popular myths about black holes. Let's address some of them. Black holes don't reach out and pull everything in. Consider a massive star with three planets, A, B, and C. Now let the star go supernova and its surviving neutron star be a black hole. Assume by some magic the planets survive that supernova just fine. Will the gravity the planets feel from the star be any stronger now that it's a black hole? NO! Since some of the star's mass was blown away during the explosion, the star actually has less gravity now that it's a black hole. It's the surface gravity, the gravity at the surface, that has increased. And it only increased because the surface is now closer to the center. If you'd gotten that close to the center while the star was still a star, you'd have been inside it, and some of the star’s mass would be pulling you upward. Now all the mass is concentrated, and you can get much closer to the center without being pulled upward. The only locations where the black hole's gravity is stronger than the parent star's used to be are places that would have been inside the parent star. Physical singularities almost certainly don't exist. There are equations that describe how gravity behaves. We've met one of them, Newton's Law of Universal Gravitation. Remember that the distance between two things attracting each other is in the denominator; as the distance decreases, the force of gravity gets stronger. Newton's Law of Universal Gravitation is not the right one, we'd need Einstein's Theory of General Relativity, but that's beyond us. So what happens to the calculation of the force of gravity when the distance between two particles in a black hole is zero? Try it on a calculator, you'll get either "ERROR" or "UNDEFINED". Talk to your math teacher, they'll tell you that division by zero isn't really undefined, it just results in plus or minus infinity. That's what mathematicians call a singularity, a value for which an equation doesn't work. Take the high school ideal gas law for example, PV = nRT. Solve it for n, the number of molecules in the system; n = PV/RT. With temperature in the denominator, at zero degrees, the equation tries to tell you that the number of molecules suddenly equals either plus or minus infinity. Does this make sense? Of course not; it just means the equation doesn't work at that value of T; you've encountered a singularity. That's precisely why scientists came up with the Kelvin and Rankine temperature scales, so that temperature could never be zero. That's why we call the idea of gravity squishing everything in a black hole to an infinitely small point a singularity. We'll call it a physical singularity, to distinguish it from its math counterpart. But if that were the only problem, couldn't we just come up with some gimmick like when we wrote new temperature scales? Sure. But there's a much more important reason why the neutron stars in black holes don't get squished down to infinitely small points; particle physics. Neutrons are made of quarks, and it's possible that the most massive black holes crush the neutron stars down to quark stars. But to keep crushing them down to infinitely small would require an infinite chain of smaller and smaller particles, and there's absolutely no reason to think that's the case. Wormholes almost certainly don't exist. Remember the quadratic equation from high school algebra? It has two solutions, a positive and a negative root. If you are using that equation to describe some physical situation, sometimes both roots have a physical meaning, sometimes only one does, and you can ignore the other. The equation that describes physical singularities (which likely don't exist, remember?) has two mathematical roots. One describes black holes. The other almost certainly doesn't have a physical interpretation, but the concept is that if it could, it would describe a situation in which gravity is repulsive instead of attractive. That gave rise to the idea of "white holes", and the even more bizarre idea that somehow the matter that makes up a black hole would be transported and emerge from a white hole, with the interdiensional connection between the two dubbed a wormhole. Never mind the fact that then the matter would be gone from the black hole, so no more gravity there, so no more black hole. I won't go into all the theoretical reasons why this almost certainly can't happen, but consider this: over 150 back holes have been found, but not a single white hole, which should be much easier to detect. (Other Types of Black Holes) Although they're not stellar corpses, so technically don't belong in this chapter, this seems like a good place to discuss the other types of black holes. (Supermassive Black Holes) In the centers of most galaxies lie supermassive black holes. Such a black hole does not form from a dying star; indeed, these black holes have masses of from hundreds of thousands up to billions of times the mass of the sun. There are many hypotheses about how these arose. Some researchers think they formed out of gas from the Big Bang, and the galaxies formed around them. Others (I'm one of them) think they formed by the coallescence of stars in the tightly-packed centers of their host galaxies. (Microscopic Black Holes) The theoretical possibility exists that microscopic black holes may have formed due to the high densities immediately after the Big Bang. Such small black holes would no longer exist today; they would have evaporated by means of an effect predicted by Stephen Hawking, and named Hawking radiation. We have not observed this, so such black holes may not actually have formed, but we can't rule them out yet. (And see below.) (Intermediate-Mass Black Holes) We have detected about a dozen black holes with masses between 100 and 100,000 times the mass of the sun; too massive to be stellar-mass black holes, and not massive enough to be supermassive black holes. Did they form by the mergers of smaller black holes? Did they form by the collisions of massive stars in dense star clusters? Could they be primordial black holes that swallowed enough matter to still be around? ----- ------ ------ (Stellar Zombies) Now let's talk about ways to reanimate a stellar corpse. (Novae and Type-1 Supernovae) Recall that most stars are binary. The more massive star in a binary pair will age faster. Let it become a white dwarf. Eventually the other member of the pair will leave the main sequence and become a giant. If the pair are sufficiently close, the giant will swell to the point where material gets pulled off of it in a stream that spins down through a spiraling whirlpool known as an accretion disk and onto the surface of the white dwarf, building up a layer of mostly hydrogen on the surface of the white dwarf. When the temperature in this layer becomes hot enough to support hydrogen fusion, this fusion will now occur at the surface of the star. The fusion will soon use up the hydrogen and stop. What we see from Earth is a star that suddenly gets a lot brighter. We call these novae. Nova is Latin for new; such flare-ups were initially mistaken for new stars. Of course, once the hydrogen layer builds up again, the same thing will happen again. Once we've seen it happen twice to the same star, we designate it a recurrent nova; there are currently ten of these known. Take a recurrent nova. Each time it erupts, it's producing helium, and building up a helium layer on the surface of the carbon white dwarf, increasing the white dwarfs mass. Eventually the mass may be increased to allow carbon fusion to ignite in the core of the white dwarf, destroying the star in a Type-Ia supernova, also known as a white dwarf supernova. (X-Ray Binaries, Millisecond Pulsars, and X-Ray Bursters) Take the binary star case above, but with more massive stars. The first one blew up and is now a neutron star, so now the second one has expanded and is dumping mass through a spiraling accretion disk onto the neutron star. Due to the higher mass of a neutron star compare to a white dwarf, the inner region of the accretion disk is much hotter than in the white dwarf case, and is a significant source of X-rays. As the stream spirals onto the surface of the neutron star at an angle, it spins it up from its initial rate of one rotation a second to perhaps a thousand rotations a second (a rotation every millisecond). If we detect that neutron star as a pulsar, we call it a millisecond pulsar. Under the higher pressure exerted by the strong gravity of the neutron star, the hydrogen layer at the surface continuously fuses at the bottom of the layer (which is only a few feet thick), converting to helium. Each time the helium layer builds up sufficient pressure, it fuses, resulting in a burst of X-rays. Star systems that do this are known as X-ray bursters.

CH 16 Star Birth

Galileo's observation of the phases of venus supported:

Corpernicus's model

During an eclipse, one object prevents us from seeing another

Eclipses are named for the object that disappears.

The universe is:

Expanding

Aristarchus of Samos (310 BC to 230 BC):

Extended Aristotle's work by measuring the size of the earth's shadow on the moon during a lunar eclipse and correctly deduced that the moon was about 1/4 the size of the earth. By comparing the angle between the moon and the sun when the terminator on the moon was exactly straight (1st quarter and 3rd quarter phases), he determined that the sun was at least seven times further from the earth than the moon and more likely over twenty times further away. Since the sun and moon appeared about the same size in the sky, the sun had to be larger than moon in the same proportion as its distance. This meant the sun had to be also larger than the earth. He then argued that the larger object (the sun) was more likely to be the central object. This argument was not generally accepted because he could not account for the lack of parallax or sense of motion.

A light-year is a unit of time True or False

False

All stars are the same size; they just differ in brightness True or False

False

An astronomical unit (AU) is larger than a light-year True or False

False

Stars are organized into:

Galaxies

In the northern hemisphere, on the first day of spring, the sun rises in the east. Where will it rise on the second day of spring?

Half a degree north of east

The new calendar begins with the end of the Saturnalia placing the Winter Solstice at December 25

In this calendar the Vernal Equinox then falls on March 25.

In which month are we closest to the sun?

January

Kepler's Laws as derived by Newton Newton applied his three Laws of Motion and the Law of Gravity to the problem of planets orbiting the sun. He found that Kepler's Laws were a natural consequence of Newton's Laws. When Newton derived Kepler's Laws, he found a more general solution. ******Kepler's 1st Law******* "Every orbit is a conic section with the central object at one focus" Conic sections: are simply slices of a cone. Depending on how you slice a cone, you get one of four possible figures. Slicing the cone parallel to its base give you a circle. Tilting the slice a bit gives you an ellipse. Slicing the cone parallel to one side gives you a parabola. Slicing the cone vertically gives you an hyperbola. Imagine this gedankenexperiment; Superman is standing on a mountaintop high enough to stick out of the atmosphere. He has a bucket of baseballs, and is throwing them horizontally. At low speed the baseball curves off and hits farther down the mountain. At higher speed it hits farther down. Keep increasing the speed, and it will hit on the plain beyond the base of the mountain. Further increases in speed cause it to strike farther* from the base of the mountain. The paths in each of these cases will be a portion of an ellipse, though it is often easier to approximate the path as a portion of a parabola. There is one particular speed (orbital speed) that will produce a circular orbit. Faster speeds will produce elliptical orbits, with the center of the Earth at one focus. There is a critical speed that is about 1.41 (the square root of 2) times the circular velocity that will produce a parabolic orbit. This is called escape speed. Any higher speed will produce a hyperbolic orbit. Kepler was concerned only with the planets, which all move on elliptical orbits, so he did not see the other possibilities. **********Kepler's 2nd Law********** "The radius vector sweeps over equal areas in equal times" Newton showed that Kepler had this one right, but that it also applied to all of the conic section orbits. ********Kepler's 3rd Law************ (M1 + M2) * P2 = a3 Newton found a whole additional factor when he derived the 3rd Law. The sum of the masses (in terms of the mass of the sun) appeared in the derivation. Kepler did not see this factor because the masses of the planets were so small compared to the mass of the sun that this factor was approximately 1 for every planet. Jupiter is the most massive planet at 0.1% the mass of the sun. This makes the sum of the masses for Jupiter = 1.001. The sum of the masses for each of the other planets is a number even closer to 1. The importance of Newton's general solution is that the relationship now applies to all orbits. If you can observe the size of the orbit of a moon orbiting a planet and its orbital period, you can solve the relationship for the sum of the masses of the planet and the moon in terms of the mass of the sun. Since the mass of a moon is typically very small compared to the mass of the planet, this gives us a means of measuring the masses of planets. The principle later extended to stars when we found cases of one star orbiting another (called a binary star). This gave us the means of determining the masses of stars with respect to the sun. ********Gravity and Tides******** The Moon's gravity pulls water towards the Moon, creating a bulge of water on the side of the Earth facing the Moon. At the same time, the Moon's gravity pulls the Earth out from under the water on the side away from the Moon, creating an equal bulge on that opposite side. Rotation of the Earth would carry a coastal town from the bulge, to the low area, to the other bulge, to the other low area, creating a pattern of high tide, followed six hours later by low tide, followed by high tide, et c. But it's not that simple. Although the Moon is the closest astronomical body to Earth and creates the highest tides, the Sun plays a role too. As massive as it is, it's also much farther than the Moon, so it's gravitational pull on the Earth is only 46% as strong. That means it raises high tide bulges pointing toward and away from the Sun, but they are only 46% as high as those from the Moon. In mid-ocean, the theoretical tides due to the Moon would be 21 inches, and 10 inches due to the Sun. When the Moon and the Sun are aligned, at New and Full Moons, their tides work together, causing higher-than-usual high tides, and lower-than-usual low tides. We call these spring tides. The use of the phrase is not from the the season spring, but simply from the fact that the high tides spring up higher than normal at those times. The opposite situation occurs at neap tides, when at the quarter moons the Sun and the Moon fight against each other. The Moon wins, and the result is that the high tides aren't very high, and the low tides aren't very low. Remember the word "Universal" in Newton's Law of Universal Gravitation? That means that theoretically, everything in the universe contributes to the ocean's tides. But the third-strongest component, the tides due to Jupiter, are too small to be measured. Tides don't just affect the oceans. The top of the atmosphere rises and falls with the tides, something people launching spacecraft have to keep track of. And the ground rises and falls, too. Ground tides due to the Moon are about 14", and 6" due to the Sun. We don't notice this because everything around us rises and falls, and we have no reference to judge it against, but it can be measured by averaging lots of GPS altitude measurements at different times in the tidal cycle. For those learning English as a second language, this sentence illustrates the use of two frequently-confused words, "further" and "farther". "Farther" refers to physical distance, while "further" is used in a broader sense for magnitudes other than distance.

Kepler's Law

When the phase of the Moon is halfway from full to new, the phase is:

Last quarter

A cloud of gas is called a:

Nebula

Newton said - "I was able to see so far because I stood on the shoulders of giants." Newton began with all of the work accomplished by Kepler and Galileo, among others, and created a whole new paradigm that created a new way of looking at the universe. Newton proposed a "clock-work" universe where cause and effect dominated. According to Newton, if you knew the initial conditions to a sufficiently high precision, everything should be predictable. Within limits, this model works quite well. Newton was a great admirer of Euclid, the Ancient Greek responsible for geometry Euclid based his work in geometry on deductive reasoning, the "if-then" style of logic; if these two things are true, then this must be true. Deductive reasoning is often more challenging than inductive reasoning, but it has the advantage of being fool-proof so long as the input statements are correct. If you select good input statements, you can then go on to prove other statements on the topic. Euclid called his twelve starting statements "axioms", and used them to build up hundreds of statements about geometry. Newton wanted to put science on a similar foolproof footing. He failed, and today science is based on experimental disproof. Newton did succeed with one narrow branch of science; the branch of physics dealing with motions and forces. He adopted as his axioms three ideas from Ancient Greece; today these are known at Newton's Three Laws of Motion. He did NOT originate these, he's simply saying that these are so simple and obvious that we can accept them without proof, and use them as our axioms to develop new statements about motions and forces, which he did in his book Principia. Much of Newton's theoretical breakthroughs occurred in the period 1665-1667 when the black plague was rampant in London. During this period, Newton returned to his family estate, Woolsthorpe (at left), where he was born. He later was elected as Lucasian Professor of Mathematics at Cambridge (a chair later held by Steven Hawking, and held in the final episode of Star Trek, The Next Generation by Data, the android). Newton's First Law of Motion (The Law of Inertia) "An object at rest tends to remain at rest, and an object in motion tends to remain in uniform, straight-line motion, unless acted on by an outside force" -newton It means any change in the state of motion of an object is due to a force. Magic does not exist. Here on the surface of the Earth, moving things eventually slow down and stop. Newton recognized that this is due to the force of friction. Since there is no friction in space, planets keep going. In Newton's day, there were people who didn't accept the idea of a force of friction, nor its absence in space; they maintained that since planets didn't slow down, and stop, they must be pushed by supernatural entities, angels. Newton is saying that we don't need the push of angels to keep planets in motion. The flip side of this argument is that an object at rest will remain at rest, unless acted on my an outside force. If I balance a white-board marker on end on a tabletop, and if magic existed, a magic-user student might be able to make that marker move. It's never happened. Consider this gedankenexperiment. Suppose I bring into the classroom a six-foot length of fine sewing thread tied to a brick, and begin whirling the brick around my head? As a student sitting in that classroom, would you be comfortable? Probably not. You're going to duck. You have, likely very early in life, developed an intuitive understanding of Newton's First Law of Motion. You know that if that string breaks, the brick will not continue circular motion around my head; instead, it will continue in straight-line motion tangent to wherever it was on its circular path when the string broke. Newton's Second Law Of Motion (The Law of Acceleration) "The acceleration of an object is related to its mass, and the force applied to it. F=ma" When a net force is applied to an object it will accelerate. The acceleration will be in the direction of the force and the magnitude of the acceleration will be directly proportional to the magnitude of the force and inversely proportional to the mass of the object. This is usually expressed by the formula: F = m * a Where "F" is the force,"m" is the mass and "a" is the resulting acceleration. Newtons Third Law of Motion (The Law of Action-Reaction) "For every action there is an equal but opposite reaction" This law explains how jet engines and rockets work. When their fuel is burned, the resulting exhaust gases take up more space than the initial fuel and oxidizer. The shape of the engine directs the exhaust gases out the back; that's the action. The reaction is that the engine (and hopefully the vehicle attached to it) goes forward. This law also explains why a gun "kicks" when fired. The expanding gas in the chamber applies a force to both the bullet and the gun (equal, but opposite). Since the gun has much more mass than the bullet, its acceleration will be less (1st Law). The bullet, with a small mass will accelerate to a very high speed as it travels down the barrel of the gun.

Newton and Motion

Archaeoastronomers have to take precession into account before deciding if some old structure had any significant astronomical alignments at the time it was built.

Precession used to be called "The Precession of the Equinoxes"

Aristotle's argument won out. He argued that if the Earth moved around the Sun, we would see an apparent shift in nearby stars, back and forth throughout the year, a shift called stellar parallax. Since that can't be seen without a telescope, Aristotle convinced folks that the Earth is the center of the universe. Two of the planets, Mercury and Venus, orbited closer to the Earth than the Sun did. Their epicycles had to stay near an Earth-Sun line. The other three planets, Mars, Jupiter, and Saturn, orbited farther out than the Sun's orbit; their epicycles were not restricted to an Earth-Sun line, allowing them to be found anywhere along their deferents. These arrangements allowed the model to account for the fact that Mercury and Venus were always seen near the Sun, while the other three could be anywhere along the ecliptic, even opposite the Sun.

Ptolemy's model was geocentric. It had planets moving on small circles called epicycles. The centers of the epicycles moved on larger circles called deferents. The Earth was near (but not at) the center of the deferent. The epicycles didn't move at constant speed around the epicycles, but they did move at constant speed as seen from the equants, points on the far side of the deferent's centers from Earth.

constellation second brightest of Orion

Rigel (Beta Orionis) Bellatrix (Gamma Orionis)

equinox

Roughly halfway between these two dates, the sun rises directly in the east and sets directly in the west. On those dates, we get equal amounts of daylight and darkness, the equinox ("equal night") date

You can tell the Moon didn't pass through the center of the Earth's shadow because the lighting is uneven

Since red light is more easily refracted than blue, the eclipsed moon often appears blood-red or copper-colored

which one do we use in everyday life

Solar day

In everyday life, our clocks are based on:

Solar days

Yes, I know, centrifugal force isn't really a force; it's an effect of inertia. But it's often useful to consider it as if it were a force

Sometimes I've run into people who think the north star is the brightest star in the night sky. It's not; it's the 49th brightest. Sirius is the brightest

Thales of Miletus (624 BC to 546 BC):

Statesman, geometer and astronomer. Most noted for using Egyptian and Babylonian astronomical records to predict an eclipse in 585 BC which led to the end of a war between two Greek factions. He was one of the first to speculate that the sun and stars were not gods, but physical objects. This was a crucial step in scientific reasoning and led to an intellectual explosion which lasted hundreds of years.

Prehistoric civilizations used observations of the rising and setting points of the Sun at solstices to keep their calendars accurate

The Homo sapiens species is hundreds of thousands of years old most of human history, hunter-gatherers would have used either crude calendars based on seasons ("Grandma died five winters ago."), or lunar calendars based on the phases of the moons. Our word month, of course, comes from the word moon.

Altitude and Azimuth system can be made percise...

There are 360 degrees in a circle. Divide a circle across the sky into 360º, and each degree is about twice the width of the full moon. If we need to specify a location more accurately than that, we can subdivide each degree into 60 arcminutes (so the full moon would be about 30 arcminutes across), and each arcminute into 60 arcseconds

It was not long before the government of Rome needed to keep track of events in the "Dark Time", this time from the ending of one calendar year and the beginning of the next. Two new months were created: Januarius and Februarius. Unfortunately, a year consisting of 12 alternating 29 and 30 day months has only 354 days in it. This is about 11 days short of the actual length of the year. This caused Marchis to slip back with respect to the Vernal Equinox by about 11 days per year

To correct this problem, the calendar keepers would let the slippage occur for two or three years. When Marchis was starting sufficiently before the Vernal Equinox, it would be stopped halfway through (the Ides of March) and a month of between 22 and 33 days would be inserted (called Mercidonius) so that when Marchis was resumed, Aprilis would start with a new moon. Unfortunately, it was left the the Prelate of each Prefecture (Region) of the Roman Empire to maintain their calendar. With no fixed rule of the insertion of Mercidonius, the calendar became chaotic. You could travel from one region to the next to find each was on a different month.

From a dark site with the naked eye, one can see thousands of stars in the night sky True or False

True

You noticed that the Moon is more lit up than yesterday, and that more than half of the circle is lit up. The phase is:

Waxing gibbous

A group of stars that forms a recognized pattern, but is not a formal constellation, is an

asterism

middle star on Orions belt is:

four times brighter, but twice as far away

the record-holder is Saturn, which is rotating fast enough to be flattened by 9.8%.

he Moon is so much closer to Earth than the Sun is that its gravity has a 50% greater effect than the Sun's gravity, and the Moon's orbit is tilted even farther from the Earth's equator. As the gravity from the Moon and the Sun battle to tip the Earth, the result is precession.

Stars use ______for most of their lives

hydrogen fuel

Earth goes around the sun

in one year

Winter Solstice (sun stand)

in the fall, if you watch where the sun rises or sets on the horizon, you will see that it moves farther south each day. Then, for a few days on either side of the shortest day of the year, it seems to rise or set at the same place.

Betelgeuse:

is a dying star, about 200 light years away

Milky way galaxy:

is about 100,000 light years away

Galaxies are:

made of stars (and their planets), gas, dust, and dark matter

the "Great Red Spot" is:

not a storm

Inverse square law:

relates brightness and distance

faintest stars we can see with the naked eye is:

several tens of thousands of light years away

Stephan's Law:

tells how much light you get per square inch at different temperatures.

The one in the spring is the vernal equinox

that in the autumn is the autumnal equinox. The dates of the equinoxes and solstices vary from year to year, but lie between the 19th to the 22nd of March, June, September, and December.

Summer Solstice (Northern Hemisphere)

the sun rises in the same spot in the northeast for several days

In the course of a year, the Sun passes through 13 constellations*, collectively known as:

the zodiac

What happens if you point the Hubble Space Telescope at a seemingly empty part of the sky and take exposures totaling 23 days?

-The result is the "Hubble eXtreme Deep Field" image below. -Covering an area about 1/15th as wide as the full moon -it contains about 5,500 galaxies -the oldest dating back to 13.2 billion years ago.

Orions Belt:

-are 3 stars

The suns temperature is:

5,780k

The Roman's Julian calendar used a year of:

365.25 days

Four thousand years ago the north star was Thuban, in the constellation of Draco the Dragon

400 years ago the star Polaris became the north star

Moon is:

a generic term for any natural objects orbiting a planet

Saturnalia:

begins at the time of the Winter Solstice and lasts seven days

Corpernicus' system was:

heliocentric

Ultima Thule:

was visited in 2019 on new years day and of this writing in march of that year -has rolling hills, troughs, pits, bright and dark areas

Pre-Greek Historic Astronomy:

We have Babylonian records of the motions of planets across the sky, Chinese records of unusual events in the heavens, Egyptian records of annual motion that they used to foretell the annual flooding of the Nile, and many more

1. The computer who initially classified stars in alphabetical order according to the strength of the hydrogen line, believeing she was measuring the amount of hydrogen was: Willamina Fleming 2. The variable star brightens quickly and dims more slowly, it is a: delta cepheid variable 3. Using the average brightnesses of delta cepheids in the small magellanic cloud, Henrietta Leavitt was able to measure that galaxy's: distance 4. A star has a parallax shift of 0.05 arcseconds. How far away is it? 20 parsecs 5. Which type of star clusters have more stars? Globular clusters 6. What is the life expenctancy of Serious A? three hundred million years 7. according to this diagram, a MS star with a luminosity of 10 to the power of 4 times that of the sun has a mass of: 10 solar masses 8. The most accurate method to determine the distance of nearby stars is based on the apparent shift of the star against the background of more distant stars as the earth orbits the sun. This method is called: stellar parallax 9. Most stars are solotary, as opposed to being in multiple-star systems. FALSE 10. The computer who arranged the spectral classification into OBAFGKM was: Annie Jump Cannon 11. According to this diagram which star is brighter? Mira 12. According to this diagram, whic star is hotter? Sirius B 13. Compared to a supergiant, a white dwarf will have: thicker spectral lines 14. who discovered that all stars are primarily hydrogen and helium? Cecilia Payne-gaposhkin 15. A star has a spectral classification of B0V. according to this diagram it is: much brighter than the sun 16. Variable stars fluctuate in: brightness 17. In order to calculate a star's absolute magnitude, I need to know its: apparent magnitude and distance 18. Which type of star clusters are still forming today? open clusters 19. Which is hotter? Spectral type B 20. The reason we paid so much attention to binary stars is that by studying them, we can determine a stars: mass 21. A star with 20 times the mass of the sun would be a(n): high-mass star 22. 21-cm radio emission provides us with a means to detect: interstellar gas 23. A star with 6 times the mass of our sun would be a(n): intermediate-mass star 24. As they age, Main Sequence stars move along the Main Sequence. FALSE 25. Bipolar jets and accretion disks are associated with: protostars 26. The process that starts a cloud collapsing is: gravitation 27. Which of the following is NOT true about the first reaction of the CNO cycle? it fuses a hydrogen-1 with a carbon-12 to prodcue gammas and a radioactive nitrogen-13, which then decays to carbon-13, a positron, and a gamma ray 28. Which of the following is NOT true about the second reaction of the CNO cycle? It fuses a hydrogen-1 with a carbon-13 to form nitrogen 14 plus neutrinos 29. Which of the following is NOT true about the third reaction of the CNO cycle? It is part of the chain of reactions by which our sun fuses hydrogen into helium 30. which of the following is NOT true about the fourth reaction of the CNO cycle? It is the major way our sun produces helium 31. Cocoon nebulae are evidence for: protostars 32. Emission nebulae provides us with the means to detect: interstellar gas 33. Extinction provides us with the means to detect: interstellar dust 34. A protostar with too little mass to become a star becomes a: brown dwarf 35. Which star undergo the helium flash when helium fusion ignites? low-mass stars 36. When fusion stops in a high-mass star, why do they implode? gravity 37. The gas in the intersteller medium is mostly: hydrogen and helium 38. The intersteller medium has more dust than gas? FALSE 39. Long-wavelength infrared emission provides us with the means to detect: intersteller dust 40. The exposed core of a low-mass star is a: white dwarf 41. Microscopic black holes have been found. FALSE 42. Molecules exist in giant molecule clouds because: the interiors of the clouds are shielded from ultraviolet light 43. The thing that determines whether a star will fall on the Main Sequence of an HR diagram is: The fusion of hydrogen into helium 44. A millisecond pulsar is the result of: material spiralling onto a pulsar from another star 45. Main sequence stars with more mass will be: hotter and brighter 46. A nova is the result of: a white dwarf collecting enough material from a companion to undergo hydrogen fusion 47. a neutron star is composed of: neutrons 48. Our sun will eventually become a black hole. FALSE 49. The next stage after the MAIN Sequence is a: Red Giant 50. Which of the following is NOT true about the first reaction of the proton-proton chain? It produces energy in the form of gamma rays 51. Which of the following is NOT true about the second reaction of the proton-proton chain? It produces neutrinos 52. Which of the following is NOT true about the third reaction of the proton-proton chain? it takes place in the convective zone of stars 53. We can detect protostars with: infrared telescopes 54. Protostars are powered by: the heat of contraction 55. Reddening provides us with a means to detect: intersteller dust 56. How are the most massive elements on the periodic table produced? by the r-process 57. The serial fusion of He to nuclei past C in high-mass star stops at which stable element? iron 58. Black holes are likely to contain singularities. FALSE 59. A supernova can leave behind: a neutron star 60. How are the odd-numbered chemical elements produced? by the s-process 61. There can be stars with 10% of the mass of the sun. TRUE 62. There can be stars with 1% of the mass of the sun. FALSE 63. The type of intersteller clouds which form stars are known as: molecular clouds 64. A stellar-mass black hole is a type of: neutron star 65. Our sun is a: low-mass star 66. Our sun will eventually: lose its outer layer as planetary nebula, exposing the core 67. A star spends most of its life as a: Main Sequence star 68. Which of the following is NOT true about the first reaction of the triple-alpha process? It takes place in a star's radiative transfer zone 69. Which of the following is NOT true about the second reaction of the triple-alpha process? It happens in Main Sequence stars 70. Which of the following is NOT true about the third reaction of the triple-alpha process? It produces neutrinos

Exam 3 chapter 15,16,17,18

1. Stars at the edge of the milky way move: about as fast as those in the centre 2. How do we know that there is a supermassive black hole in the centre of our Milky Way galaxy? by the radio emissions from gas orbiting it. 3. What broke up the gas in the early universe into the clumps that would become galaxies? sound 4. Most of the Milky Way's globular clusters are located: in the halo 5. Our Milky Way galaxy is part of a small group galaxies called the: Local Group 6. The name of our galaxy is the ____galaxy. Milky Way 7. Most of the mass in the Milky Way is located: in the halo 8. Most of the mass in the Milky Way is in the form of: dark matter 9. Which part of the Milky Way galaxy has lots of gas and dust, and new star formation? The disk 10. Our Milky Way is a(n): spiral galaxy 11. Which stars are older? Population II 12. Streams of star that revolve backwards in the Milky Way are evidence: that the Milky Way has swallowed small galaxies 13. Which direction is this galaxy rotating? It's impossible to tell from the picture (spinning counter clockwise) 14. The Milky Way's spiral arms are located: in the disk 15. Our sun is in the Milky Way's: disk 16. Superbubbles: are the combined clouds of gas from multiple supernovae 17. We've called the diffuse band of light in the sky the Milky Way since Ancient Greek times, but when did we realise that stars in the universe are clumped into the gigantic clumps we call galaxies, of which the Milky Way is but one? In the early 20th century 18. Dark matter is more likely to consist of: WIMPs 19. Most of the dark matter in barred spirals is in: the central bulge and bar 20. Most of the dark matter in elliptical galaxies is: in the centre 21. Most of the dark matter in the Milky Way is in: the halo 22. Which looks more round? An E0 23. Early galaxies were: smaller than today 24. Which galaxies have more dust? Spirals 25. Which is true? Spiral galaxies can merge to become elliptical galaxies 26. Which galaxies have distinct internal structure? spirals 27. What classification is our galaxy? SBbc 28. Which galaxies have little or no gas & dust? Elliptical 29. Which galaxies have little or no new star formation? Ellipticals 30. Sa galaxies have: Large bulges and tight arms/ 31. Which galaxies are the smallest? Irregulars 32. Why are the spiral galaxies blue? their gas & dust provides lots of star formation, so they have short-lived O- & B- type stars 33. Our Local Group is part of the ___ cluster of galaxies. Virgo 34. Which galaxies are yellowish? Ellipticals 35. How many fundamental forces are there? 4 36. Protons are fundamental particals. FALSE 37. Astronomers have a scientific explanation for what caused the Big Bang. FALSE 38. There is evidence to support the Big Bang theory. TRUE 39. Which class of particles can occupy the same space? Bosons 40. At the moment of he Big Bang, the universe began expanding outward from a central point. FALSE 41. If i slam my finger in the door, my pain is caused by the application of which fundamental force? The electromagnetic force 42. In the early universe, the temperature was: hotter than today 43. Electron are: leptons 44. Which two forces were the first to be unified, in the early 80s? The electromagnetic force & The weak nuclear force 45. During which era did helium nuclei first appear? The era of nucleosynthesis 46. Electrons and quarks both belong to which class class of particles? fermions 47. There should be life on Earth until the sun becomes a red giant and engulfs the Earth. FALSE 48. Gluons carry which force? The strong nuclear force 49. Which is most massive? The tauon 50. A neutron is composed of: two down quarks and an up quark 51. During which era did protons and neutrons first appear? The particle era 52. Photons of light are: bosons 53. Photons carry which force? The electromagnetic force 54. Protons are: baryons 55. Which fundamental force holds an atomic nucleus together? The strong nuclear force 56. There was a time before the Big Bang. FALSE 57. When a proton changes into a neutron, releasing a positron and neutrino, which fundamental force is involved? The weak nuclear force 58. The weak nuclear force is carried by: The W+, W-, and Z0 59. How is it likely that life elsewhere in the universe is carbon-based? Quite likely 60. How likely is it that life elsewhere in the universe is organised into cells? We just don't know 61. Which of the following is NOT true about the Drake Equation? It tells us precisely how many communicating civilizations to expect 62. Scientists have a precise definition of life. FALSE 63. We hope to be able to detect microbial life on other planets fairly soon (in the next few decades). That hope is based on: detection of waste gasses in the planet's atmosphere 64. Are your professor's pet parakeet's pancreatic cells' protein's phosphorus atoms' protons alive? No 65. How likely is it that life elsewhere in the universe uses water as a solvent? Fairly likely, but other choices are rather likely, too

Exam 4

Corpernicus' system explained retrograde motion using epicycles

False

Heavy objects fall faster than light objects True or False

False

Science attempts to prove ideas about nature True or False

False

The Earth revolves around its axis True or False

False

Tycho Brahe was the first astronomer to use a telescope

False

Tycho Brahe's Tychonian system was heliocentric True or False

False

Wein's Law says that hot stars glow more red, cold stars glow more blue True or False

False

The tropical year is defined as the time from one vernal equinox to the next, though sometimes the mean tropical year is used, which is the average of the four seasonal years

In 2000, the mean tropical year was 365 days, 5 hours, 48 minutes, and about 45 seconds. This is close to the time interval between two vernal equinoxes; they would be identical were the Earth's rotation not slowing by 1/2 second per century due to tidal effects from the Moon

We can measure how far north or south any location (called its latitude) is by assigning the equator to be 0º, then measuring north or south from there

In the late 1700s, when this system first came into widespread use, each country tended to use their own capitol. The British had the most powerful navy, so now the internationally recognized starting point is a line from the North Pole to the South Pole, passing through the base of a particular telescope at the Royal Navy Observatory in the London suburb of Greenwich (pronounced "grin-itch"). This line is called the Greenwich Meridian or the Prime Meridian, and places are specified as so many degrees east or west of this line

in the (northern hemisphere) in the summer, the sun rises fairly far north of east, climbs fairly high in the southern sky by midday, and sets fairly far north of west. Days are long, and it's hot

In the winter the sun rises fairly far south of east, stays fairly low in the southern sky at midday, and sets fairly far south of west. Days are short, and it's cooler. So it seems the temperature swing has something to do with how high the sun is in the sky, and most of us remember that the tilt of the Earth has something to do with it.

The celestial equivalent of latitude is declination, which is a direct projection of latitude onto the sky. If longitude were projected directly onto the sky, the grid lines would sweep across the sky as the Earth rotates, and we would have the same problem as with azimuth; the coordinate of a star would change constantly. Instead, we use a system similar to longitude, but anchored in the sky rather than on the Earth, a system called right ascension.

Instead of a line from the north pole to the south pole through Greenwich, right ascension uses a line from the NCP to the SCP through the vernal equinox point, which is the location of the Sun on the first day of spring (the vernal equinox). Locations are then specified around from this poin

What was radical about the scientific method was that it didn't seek proof?

It sought to test every new idea, not to prove it, but to attempt to disprove it. If an idea could not be disproven, it was not considered proven, it was only given a higher level of acceptance. No idea in science is ever considered proven. At first glance, this seems an unsatisfying philosophy; pessimistic, defeatist, even nihilistic. In practice, it has turned out to be just the opposite. By freeing us from the necessity of seeking absolute proof of any idea, the scientific method has freed us to devote our energies to testing an idea to whatever level of acceptance we require, then moving on. Much has been accomplished in the past 400 years because of this.

Galileo: Galileo was a contemporary of Kepler. While Kepler lived in Northern Europe, Galileo spent most of his life in Italy. Galileo is most noted for his studies in physics and the use of the telescope to view celestial objects. Galileo did not invent the telescope. the telescope was invented in northern Europe around 1607. It has been suggest that a young optician by the name of Hans Lippershey in Holland was the inventor. By late 1608, "optic tubes" were being sold in many European cities as novelties. A friend of Galileo saw one in Paris and wrote him about it. Galileo immediately recognized the principle of the instrument and had built his first one a few months later.

Galileo was one of the first to use a telescope to observe the heavens. His observations dealt a severe blow to the Ptolemaic model. One of the arguments for the geocentric view was that the moon obviously revolves around the earth. If the earth went around the sun, why does not the moon get left behind? Galileo observed Jupiter and found four star-like bodies revolving around it. We now call these the Galilean satellites of Jupiter. Since Jupiter must move in any planetary system, the fact that there are several bodies that travel with it negates the problem of the moon revolving around the earth.

In what month are we farthest from the sun?

July

Galileo (Continued) Galileo also observed Venus and discovered that it exhibited a full range of phases as it moved from one side of the sun to the other and back. This meant that Venus had to revolve around the sun and could not spend all of its time between the earth and sun. This was evidence against Ptolemy's model. Galileo observed that powdery band of light surrounding the sky that we call the Milky Way. He found that it was composed of stars too faint to be seen without the telescope. While the stars were too faint to be seen individually with the unaided eye, there were so many of them their combined light produced the Milky Way. Galileo argued that there was much more to the Universe than what was apparent to the unaided eye.

Galileo wrote to Kepler in 1610: "You are the first and almost the only person who, after a cursory investigation, has given entire credit to my statements. ... What do you say of the leading philosophers here to whom I have offered a thousand times of my own accord to show my studies, but who, with the lazy obstinacy of a serpent who has eaten his fill, have never consented to look at the planets, or moon, or telescope."

Pythagoras (580 BC to 520 BC):

Geometer and astronomer. Most famous for his Pythagorean Theorem, that for a right triangle, the square of the length of the hypotenuse (the longest side) is equal to the sum of the squares of the other two sides. One of the first to propose an astronomy-based argument that the Earth is a sphere. Earlier civilizations had argued the Earth must be spherical, but their arguments were based on what we see here on Earth, notably that a ship sailing away, or a person walking across a flat plain, will seem to sink lower as they move farther away. Pythagoras presented additional proof that the earth and other celestial bodies were spherical based on the idea that since the phases of the moon proved the moon must be a sphere, the Earth, by analogy, must be as well. He initially taught that the earth was at the center of the universe, but later some of his students argued that the earth and planets moved around the sun.

Greek Astronomy: The Greeks put great faith in the power of logic. They would start by assuming that what appeared to be "obviously" true was true. Logic would then lead them to other "truths". If later observations did not agree with the "truths" arrived at by logic, then it was assumed that there was something wrong with the observations. The Greeks were also big on "causes"; they wanted to understand why things happened

Greek writings (c. 600 BC to AD 150) were very influential in the development of our modern ideas about astronomy Our word "planet", comes from their word "planetes", meaning "wanderer" Most stars were fixed stars that stayed in their constellations, but there were the five planetes, the wandering stars: Mercury, Venus, Mars, Jupiter, and Saturn. Greeks knew the Earth was round in Columbus' day, Europeans thought the world was flat (That was misinformation from several writers in the 1800s, including Washington Irving) Greeks ideas of logic, and their discussions of inductive and deductive reasoning

The calendar we use today is the:

Gregorian Calendar

To honor Julius Caesar for this improvement to the calendar, the Roman Senate changed the name of Quintilis to Julius (our July). Two years later, in 42 BC, Julius Caesar was killed on the Ides of Marchis

Legend has it that the rule for adding the extra day to Februarius, called the leap day, was poorly worded and the day was added every three years instead of every four for the next couple of decades. When the error was noted, Julius' successor, Augustus Caesar, had the rule reworded and also adjusted the calendar to put it back into step with the seasons. Again the Senate honored the Emperor by renaming Sextilis to Augustus. The legend further holds that Sextilis only had 30 days while Julius (formerly Quintilis) had 31. Since Augustus' month could not have fewer days than Julius', a day was taken from Februarius (already short and now having 28 days normally and 29 in leap years) and added it to Augustus. This now accounts for the order, length and names of the months as we have them today.

NGC means:

New General Catalogue

There are four named phases and two sets of adjectives used

New moon - When the moon is near the sun, it's unlit side is facing us and can't be seen against the sun's glare Full moon - The opposite position presents the lit side to us At right angles to these are the first and third (or last) quarters As the moon moves from new to full, the illuminated portion grows each night, so we use the adjective waxing, meaning "growing". From full moon to new moon, the illuminated portion is waning, or shrinking From first quarter to third quarter, the illuminated portion bulges out past halfway, so we use the adjective gibbous, meaning "bulging" From third quarter to first quarter, less than half of the visible face of the moon is illuminated, presenting a crescent shape

********Newton's Law of Universal Garvitation************* Let's think about some of the forces known in Newton's time. There was gravity, that made things fall here on Earth. There was the force that Kepler argued pulled planets towards the Sun. Newton agreed with this assessment, since Newton's First Law of Motion says that planets would wander off in straight lines were there not some force pulling them toward the Sun. By the same argument, there was a (third) force with which the Earth held the Moon in orbit. And since Galileo observed four moons orbiting Jupiter, Jupiter must exert such a force as well. And there was the force the Moon exerted on the ocean, causing the tides. One thing geniuses like Newton are good at is seeing connections between seemingly disparate things. Newton saw that all of these forces could be described by the same equation, an equation that included the masses of the objects, the distance between them, and a constant. Since in one incarnation this force already had a name, gravity (Latin for heaviness), that's the name he adopted. Once Newton arrived at the formula describing these five forces, he made a huge intellectual leap for what today seems to us to be a very non-scientific reason. Like the other Renaissance astronomers we've discussed, Newton was deeply religious. He essentially argued that God is fair, and if God were handing out gravity, He would not give it to just five things, but would give it to everything. On this basis he concluded that all masses exert a gravitational pull on all other masses. Not only do planets have gravity, so do asteroids, houses, people, pillows, beetles, and dust specks. But the constant in the equation is really small, so it takes a large mass like that of an asteroid for us to be able to notice the pull of gravity. *Gravity is the weakest of the four known forces. Consider this. A refrigerator magnet is not very strong, as magnets go. Yet it is capable of holding itself on your refrigerator, withstanding the gravity pull of an entire planet!

Newton and Gravity

which is smaller? - Our solar system - Our milky way

Our Solar System

Galileo (continued) Eventually, Galileo was called before the Inquisition and forced to recant his teachings that the earth moved. While his belief never wavered, he could not publicly admit those beliefs. He was very much aware that only a decade before, Giordano Bruno had argued not only did the earth move, but that the moon and planets were other worlds just like the earth and that the stars were objects just like the sun with inhabited planets orbiting them. For this and other heresies, Bruno was burned at the stake in 1601 After his conviction by the Inquisition, Galileo spent the last 17 years of his life under virtual house arrest. He was able to continue his research, but he was prohibited from teaching. Much of his work during this period dealt with the physics of motion.

He discovered the principle of the pendulum (that the time of one swing is independent of how far the pendulum swings in any one stroke). He demonstrated that all objects fell towards the earth with the same acceleration regardless of their mass, and measured that acceleration due to gravity to be 32 feet per second squared - a falling object gains 32 feet per second of speed for every second that it falls. He found that balls of different mass (i.e., wood and iron) rolled down ramps at exactly the same rate. He reasoned that as the ramps became steeper, both would move faster by the same amount until the ramps were vertical and the balls falling. This observation was in direct contradiction of ******Aristotle who had said that heavier objects fell faster than light objects. What had confused Aristotle was the effect of air friction. It was Newton who finally explained why this was so.

Kepler: Shortly after Tycho's death, Kepler gathered up Tycho's 20 years of observation and returned to Poland. Over the next 20 years, Kepler used these very precise observations to determine the actual motion of the planets. He knew the accuracy of Brahe's observations and assumed that any model of the motions of the planets that did not fit the observations within their precision could not be correct. Kepler quickly demonstrated that neither the Ptolemaic model, nor the Copernican model (which includes Tycho's model as well) fit the observations. All had unacceptable errors.

He threw out all assumptions except his gut feeling that the sun, being the largest object of the solar system was probably at the center. Kepler realized that not only did the planets not travel on circles, they did not move at constant speed. Over the next five years, he developed a method to determine the actual motion of the planets (Mars in particular because it exhibited the greatest errors in the other models) and then set about to determine which geometric pattern best fit the observations. This led to his First Law of Planetary Motion.

Which ancient Greek developed the "apparent magnitude system" of describing the relative brightness of stars?

Hipparchus of Rhodes

Speed is distance per time; miles per hour, meters per second, furlongs per fortnight, et c. Velocity is speed plus direction; 45 mph is a speed, 45 mph northward is a velocity when we studied Galileo, we learned about acceleration, a change in velocity Galileo learned that the acceleration due to gravity is 32 feet per second squared; a falling object gains 32 feet per second of speed for every second that it falls. But acceleration can also be a change in direction. Momentum is mass times velocity, think of it as the amount of "oomph" an object has because it is moving. I can change an object's momentum by changing either its mass or its velocity The brick had more momentum I get some kind of high-tech gun that fires it at you at several thousand mile per hour. Same mass as the first marshmallow, but more velocity, so more momentum. let's leave this experiment as a gedankenexperiment A force is an interaction that will change the momentum of an object, usually by changing its velocity (changing either its speed or its direction). Consider a planet in a circular orbit; it will move at constant speed, yet under our definition of momentum, its momentum will be constantly changing because its direction is changing. Sometimes we want a number that ignores the change in direction; that's angular momentum. It also applies to rotating objects. We won't need a formal definition of angular momentum; just be aware that when the book mentions it, it's like momentum, but for rotating or revolving objects - it's a measure of the "oomph" they have because they're moving masses. The equivalent of force in these cases is torque. (difference between mass and weight) -Mass is how much material something has -weight is the pull of gravity on that material I have a certain amount of mass, and as a result of that, the Earth pulls on my with a certain weight. If I go to the Moon where gravity is less, my mass won't change, but my weight will decrease. Pay special attention to the textbook discussion of weightlessness, and gravity in orbit. when astronauts are floating in the International Space Station, it's not because they're above the Earth's gravity, it's because their orbital motion is providing an effective centrifugal force that's canceling the effect of gravity.

Physics of Motion

Any attempt to discredit this concept could be considered heresy. In the introduction to Revolutions, Copernicus justified his arguments as follows:

"... according to Cicero, Nicetas had thought the earth moved, ... according to Plutarch certain others had held the same opinion ... when from this, therefore, I had conceived the possibility, I myself also began to meditate upon the mobility of the earth. And although it seemed an absurd opinion, yet, because I knew that others before me had been granted the liberty of supposing whatever circles they chose in order to demonstrate the observations concerning the celestial bodies, I considered that I too might well be allowed to try whether sounder demonstrations of the revolutions of the heavenly orbs might be discovered by supposing some motion of the earth. ... I found after much and long observation, that if the motions of the other planets were added to the motions of the earth, ... not only did the apparent behavior of the others follow from this, but the system so connects the orders and sizes of the planets and their orbits, and of the whole heaven, that no single feature can be altered without confusion among the other parts and in all the Universe. For this reason, therefore, ... have I followed this system."

Nicolas major work (Six Books Concerning the Revolutions of the Heavenly Spheres or just Revolutions for short), he stated: * he still kept to the concept of absolute motion (on circles at constant speed). He was, however, considering that if the earth moved around the sun, it would be possible to describe the relative motions of the planets more simply. Copernicus was very much aware of the potential dangers in proposing a sun-centered system. The Christian Church (later to become the Catholic Church) had, for centuries, adopted the Ptolemaic system as "Truth".

"... the planetary theories of Ptolemy and most other astronomers, although consistent with the numerical data, seemed ... to present no small difficulty. For these theories were not adequate unless certain equants were also conceived; it then appeared that a planet moved with uniform velocity neither on its deferent nor about the center of its epicycle. Hence a system of this sort seemed neither sufficiently absolute nor sufficiently pleasing to the mind." "Having become aware of these defects, I often considered whether there could perhaps be found a more reasonable arrangement of circles, from which every apparent inequality would be derived and in which everything would move uniformly about its proper center, as the rule of absolute motion requires."

Then suddenly their clocks are an hour ahead of ours (if we went eastward), or an hour behind (if we went westward)

(For example, much of China keeps the same time, resulting in 12:00 P.M. being as much as 4 hours off from when the sun is highest in the sky.)

Bonner Durchmusterung

(The Bonn Thorough Mustering of Stars) is another famous early star catalog; you'll recognize stars listed in it as starting with BD followed by a string of numbers.

Sidereal day

(the Earth's actual rotation period) is not the day length we base our clocks on -23 hours and 56 minutes =23.933 hours

Sidereal month

(the Moon's actual revolution period) is not the one we base our calendar months on, so also the sidereal year is not the basis for our calendar year.

-3.8x10^-6 is:

-0.000,003,8

-3.8x10^6 is:

-3,800,000

Dionysius Exiguus

-6th century monk/historian -proposed the dating years from the birth of Jesus. -made his best estimate based on the historical records available to him and called that the Year 1 AD (Anno Domini) -Since the use of zero as a counting number did not come into use until the 13th Century, 1 AD is preceded by 1 BC and there is no Year 0 -Modern historical records suggest the Dionysius may have been off by a few years and that Jesus was probably born between 7 BC and 4 BC

Our Sun:

-Also called "Sol" -the word "Sun" means whichever star your orbiting around -is one of 250,000,000,000 stars in our galaxy (known as the milky way) -Will never explode -has been fusing hydrogen into helium for 4.54 billion years, and will keep on doing so for about another 7 billion years -After that it will switch to fusing helium into carbon and oxygen. It won't do that for long; about 0.01 billion years -During that time it will swell into a red giant star, engulfing and vapourizing the Earth -After that its outer layers will expand and drift away in a prettily-glowing shell called a planetary nebula -After the Sun's outer layers drift away, the dead core of the Sun will be exposed, an Earth-sized ball of carbon known as a white dwarf -Eventually white dwarfs will cool off and crystallize; the crystalline form of carbon is diamond

there are 2 celestial coordinate systems

-Altitude and Azimuth -equatorial

Pleiades cluster:

-Brightest star cluster up and to the right of Orion -also known as the Seven Sisters or as Subaru -it's 444 light years away

The Moon is a natural satellite of the Earth. It is a ball made mostly of rock, perhaps with a small metal core. Its diameter is about the same width as that of the lower 48 states of the US, from California to Carolina. It circles the Earth roughly a quarter million miles away. Were the Earth reduced to a desktop globe a foot across, the Moon would be the size of a large orange, circling some 20 feet away.

-Do we note the moon's position against the background stars and wait until it comes back to the same Right Ascension again? Such a period is called the sidereal month, 27.3 days. -Or do we count from full moon to the next full moon, a synodic month of 29.5 days?

equatorial bulge is 13.29 miles in radius, or 26.58 miles in diameter

-Earth really does bulge outward at the equator -Earth has an equatorial bulge -Earth's axis is tilted by 23.5 degrees relative to the ecliptic (the plane of the Earth's orbit), -so the Sun's gravity tries to pull that bulge down (or up, depending on the time of year) into the ecliptic

Jonann Bayer in 1603

-Gave each star the name of its constellation preceded by a letter of the Greek alphabet which usually represented its brightness ranking within that constellation -

Sirius:

-Is 25 times brighter than the sun -only 8.6 light years away from us -its the 5th closest star system to us

Uranus:

-Is a Jovian world -scientist no longer consider it a gas planet -first planet discovered -was discovered before it was discovered under the name "george" -its tipped on its side -is the coldest planet -has the most extreme seasons of any planet -there may be diamond rain into a liquid diamond sea with diamond bergs afloat in it -may be water ice in which just the oxygen froze, leaving the hydrogen atoms running around in between. -has Shakespearean moons, one of which is the least understood moon in the solar system

NGC 1300:

-Is a barred spiral galaxy -has a supermassive black hole that has 73 million times the mass of our sun

Alnilam:

-Is the brightest star in Orion -The middle star in Orion belt -Is ten times farther away than Betelgeuse -Is much hotter (27.500K) -Gives off more than 800,000 times as much light as our sun

Ring Nebula:

-Located in the constellation Lyra

Jupiter:

-Never comes between Earth and the Sun -is the largest of the gas giant planet -is one of the two varieties of Jovian planets -has rings (all 4 of our Jovian worlds have rings)

slow wobble of the Earth every 25,772 years is called:

-Precession The Earth's axis wobbles just like the axis of that top is wobbling. What causes it? The Earth isn't a sphere, the Earth isn't alone, and it's tipped.

If you were at the North Pole, the stars would neither rise nor set, but move parallel to the horizon. If you were at the equator, all stars (even Polaris, since it isn't precisely at the North Celestial Pole) would rise perpendicular to the eastern horizon, cross the sky, and set perpendicular to the western horizon

-Remember that rotation is motion around a line passing through the object; -the Earth rotates on its axis once a day. -Revolution is motion around a point outside the object: -the Earth revolves around the Sun once a year

Vesta (professor favorite astroid)

-Some asteroids are very primitive, but the largest ones melted and developed iron cores -Although only 2% of the meteorites that fall to earth are iron meteorites, they account for 22.4% of all known meteorites

Topography Map:

-The colour-coding is for elevation -blue is the lowest -up through green, yellow, orange, pink, brown, white

Horsehead Nebula:

-The head of that horse is about 3 to 4 light years tall; that's a very large horse! -The Horsehead Nebula was discovered by a well-known astronomer, Williamina Fleming

daylight period was often divided into 12 hours. The long summer days meant 12 long summer hours, while the short winter days meant 12 short winter hours.

-The length of the daylight period changes seasonally -our day/night cycle is the result of the rotation of the Earth

One way around that is to figure travel times using the ultimate speed, the speed of light. 186,000 miles per second. 300,000 kilometers per second. 670,000,000 miles per hour

-To accelerate anything with mass to the speed of light would result in infinite mass and require infinite energy -That's why only massless objects, like photons, can move that fast -In terms of travel time at the speed of light, the Moon is 1.28 seconds away (We could say its distance is 1.28 light-seconds) -The Sun is 8.33 light-minutes away -From the Sun to Pluto is 5.48 light hours. -The distance to the nearest star, Proxima Centauri, is 24,900,000,000,000 miles, which works out to 4.24 light years. -Our Milky Way galaxy is disk-shaped, 100,000 light years across. -The nearest comparable galaxy, Andromeda, is 2,540,000 light years away. -The radius of the observable universe is 13,800,000,000 light years

Little dipper is in:

-Ursa Minor

"paleoastronomy", which is the study of the relationship between the events in the historical record and astronomy

-When I study what the construction of Stonehenge by prehistoric peoples tells me about what those folk knew about astronomy, that's archaeoastronomy. -When astronomers recently used astronomy to pin down the date and time of Mary Wollstonecraft Shelley's terrifying dream that led her to write "Frankenstein", that was paleoastronomy.

Below Alnitak you see:

-a dark wall of dust along the red emmission nebula called "Horsehead Nebula"

Orion Molecular Cloud:

-a huge, nearby cloud of gas and dust, larger in our sky than the constellation Orion. -Stars have started to form in one part of it. -The fresh, intense stellar wind from those baby stars has blown a bubble in the molecular cloud; the bubble is lit from the inside, and glowing with the red fluorescence from hydrogen gas. It's called the Orion Nebula -The nebula to the left of the dark dust lane is also part of the Orion Molecular Cloud; it's called the Running Man nebula. Can you say, "pareidolia"?

Light colored blob above Alnitak is:

-a reflection nebula called "the Flame Nebula"

under a Hubble Space Telescope, the Orion nebula is:

-about 24 light years across

Pope Gregory XIII

-addressed the rule for Easter in 1580 -By this time, the Vernal Equinox, under the Julian calendar, occurred on March 11 -Pope Gregory was concerned that if this was left to continue indefinitely, it would be possible to celebrate Christmas and Easter on the same date -

Saturn:

-another gas planet -Jupiter's mini-me -has rings -known for its diverse suits of moons

stars with "Al -" :

-are arabic names in the arabic language -Al means "the"

Meteorites:

-are pieces of astroids -if bigger than a golf ball size, they will make it through the atmosphere -Barringer Crater in Arizona (below) was formed about 50,000 years ago by the impact of an iron meteorite roughly 150 feet across. The crater is also sometimes called Meteor Crater

The universe:

-began 13.8 billion years ago -the beginning was called "the Big Bang"

Betelgeuse

-brightest star in Orion (aka "Alpha Orionis"

Sirius

-brightest star in the sky

Julius Caesar:

-directed the correction of the calendar -followed the advise of cleopatra's atronomer (Sosigenes) -wanted to shift the beginning of the year to the time of the Winter Solstice (and Saturnalia)

Aldebaran (brightest star in Hyades star cluster)

-is NOT part of Hyades star cluster -it's 65 light years away

Neptune:

-is a Jovian world -scientist no longer consider it a gas planet -farthest from the sun -the first planet whose existence was predicted -its rings changes -one of its moons is really a captured Kuiper Belt (an object that spouts liquid nitrogen geysers)

Scientific notation:

-is a short hand way of writing -In scientific notation, we express a number as a decimal number with one non-zero digit to the left of the decimal, multiplied by ten to the appropriate power

Solar system

-is gravitationally bound, meaning that the things in it are held in orbit around the Sun by the Sun's gravity -Since the name "Solar system" comes from the name of our particular star, Sol, we really can't call those other systems solar systems; we call them stellar systems or planetary system -has four terrestial planets (Mercury, Venus, Earth, Mars) with another terrestial world, Luna (Moon), in orbit around Earth -has four Jovian worlds (2 gas giants; Jupiter & Saturn, 2 water giants; Uranus & Neptune)

Big dipper:

-is not a constellation, it is part of the constellation of Ursa Major (the great bear)

Betelgeuse:

-is now fusing helium into carbon and oxygen -is swollen to the size or Mar's orbit -In 100,000 will explode as a supernova -Its temperature is 3,600k -It gives off less light per square inch than the sun. -Is bigger than the sun, so it gives off 100,000 times more light -Is not the brightest stars in Orion (Alnilam is the brightest)

Pluto:

-its moon called "Charon" -has a thin atmosphere -is a is considered to a a kuiper belt object -a dwarf planet

Mars:

-known as "the red plant" -its an intermediate case between the Moon and Mercury (which are geologically pretty dead) -it was developing tectonic activity when it cooled (its frozen in time now) -like earth, it also lost substantial amounts of its atmosphere -used to have water on its surface (streams, lakes, a shallow ocean) -water was there from about a quarter billion to two billion years ago -the lower hemisphere is lower than the southern hemisphere -its smoother -its closest to the asteroid belt (hense the splats on the planet) -one big splat called "Hellas Planitia" is the size of the U.S. -the big pink and brown blob that straddles the equator on the left is called "Tharsis" (not a continent) -home to the largest volcano in the solar system -has impressive rift valleys

Hyades star cluster

-located between the Pleiades and Orion -it's 153 light years away

Constellation:

-means with stars -there are a formal set of 88 of them

Mercury:

-mostly grey world

Most if not all galaxies have a supermassive black hole in their centers, formed by the mergers of stars in such crowded areas

-normal black holes are the corpses of massive stars

The Big Bang:

-produced Hydrogen and helium -About three minutes after the Big Bang, the universe had sufficiently cooled that the elementary particles known as quarks could clump together to form protons and neutrons. During the next 17 minutes, protons and neutrons merged and got knocked apart again, until by 20 minutes after the Big Bang, the universe consisted of nuclei of hydrogen and helium atoms floating in a sea of electrons and radiation. We think that at this point, the atomic nuclei consisted of 90% hydrogen and 10% helium.* By about 377,000 years after the Big Bang, temperatures cooled off enough that electrons could start orbiting atomic nuclei; the hydrogen and helium nuclei became hydrogen and helium atoms, and the universe became transparent. From then until the universe was half a billion years old, it was full of transparent clouds of hydrogen and helium gas. No stars yet, so no light.

Sosigenes

-proposed the Romans to divorce the calendar from the moon -To keep their twelve months, one day was added to each of eleven months giving alternating 30 and 31 day months (only Februarius was left with 29 days) -The actual length of the year had been determined to be 365.25 days. -proposed every four years, an extra day would be added to Februarius (giving it 30). This would produce an average length for the calendar year of 365.25 days.

nebula:

-smudges of red light -means "cloud" in Latin -clouds of hydrogen gas that are fluorescing under UV (black light) from a nearby star

Polaris

-the North or Pole star

The really light blob below the Belt is:

-the Orion Nebula (the brightest reflection nebula in the sky)

a light year is:

-the distance light travels in a year, that means that the speed of light is one light year per year

Earth moves in different ways (we will only discuss 3)

-the rotation on its axis once a day, -the revolution around the Sun once a year, -the slow wobble of its axis every 26,000 years

Oort cloud:

-they consist of dirty snow, ices, and various compounds, and include grains of carbon compounds, minerals, and metal -When Oort cloud objects come into the inner Solar system, the heat of the sun drives off clouds of steam and dust, often leaving tails across space. We call these comets -when oort clouds objects come near the sun, we call them "comets"

the parsec

-third distance unit -(The origin of the parsec is covered in the sequel to this course, AST 104, Stars and Galaxies.) A parsec is 3.26 light years

Earth:

-third rock from the Sun -the only world with liquid water on the "surface" -missing 99% of its air -has a set of self-catalyzing chemical reaction called "life" -the fifth-largest planet circling our Sun -is one of the 8 planets on our solar system

Nuclear fusion in stars:

-turns hydrogen into more helium, and then turns helium into carbon and oxygen. -In low-mass stars like our sun, some of that carbon and oxygen gets sprayed out into the universe on stellar winds, but most of it remains locked away inside the stellar corpses known as white dwarfs. -In high-mass stars, nuclear reactions produce the other chemical elements on the periodic table; these stars then explode as supernovae and spatter that raw material out into the universe where the atomic nuclei can gather electrons to become atoms, which can then react to form molecules. -By the time it's all cooled off again, what's left is a nebula, a cloud of mostly hydrogen and helium gas, with cosmic dust grains of minerals or metal, coated with ices. -As gravity pulls the gas into clumps that will become stars, gas and dusk form swirling accretion disks around the stars. - As the dust grains collide and stick, they form into planets. Close to the star, the ice gets vapourised off the grains, so they consist only of minerals and metal. -The result is planets of rock and metal, like our terrestrial planets. Farther from the star, the cold grains still bear their mantles of ices, so the planets can grow larger. -If any planet grows large enough, it will have enough gravity to collect hydrogen and helium gas from the surrounding nebula. -All four of the outer planets in our solar system did this, and became the Jovian planets. (There are at least two other sorts of planets; rock and metal worlds that grow large enough to collect hydrogen and helium, and rock, metal, and ice worlds that do not.)

Allende (meteorite)

-very famous in space science -It's a carbonaceous chondrite, dark because of all the organic (carbon-rich) material it contains -In these meteorites we have found many of the building blocks of life, formed before the planets formed.

Venus:

-very similar to earth in mass, size, and geology -have continents like earth but different -have tectonic plates (tectonic styles are different) have 3 known styles -has right amount of air -has geological activity like earth

first major country to adopt the Gregorian calendar

-was Russia The switch to the new calendar came in 1917 with the Bolshevik Revolution when the error between the calendars had increased to 13 days.

Roman civil calendar

-was a lunar calendar -it started with the first new moon after the vernal equinox -used today for business and commerce -legend says it was created by Romulus and Remus with the founding of Rome in 758 BC. -Of course they did not use the system of numbering years (AD and BC) that we currently use -Each month after that began with another new moon. -Since the time from one new moon to the next is about 29.5 days, -the Roman months alternated between 29 and 30 days in length. -The first four months were named after various gods: Marchis, Aprilis, Maius and Junius. The remaining months were just numbered: Quintilis (5), Sextilis (6), Septembris (7), Octobris (8), Novembris (9) and Decembris (10). -Decembris ended near the Winter Solstice and the Romans celebrated this end of the year with the Saturnalia. The calendar was then put away until the next Vernal Equinox. -It was the task of the astronomers to track the motion of the Sun with respect to the stars to tell the people when the next year started

Council of Nicea

-was the first major conferences of young christian church -established the official dates of various religious holiday -Christmas was left on December 25 where early Christians chose to celebrate the birth of Jesus (which was actually in the spring)* at the same time the Romans were celebrating the Saturnalia to avoid persecution -With the Romans busy with their own major celebration, they tended to ignore the Christians. -they set the date for the celebration of Easter to be the first Sunday after the first Full moon after the Vernal Equinox -Easter can occur anywhere in the six week period following the Vernal Equinox.

The fusion of hydrogen into helium happens in one of two ways:

1. Less-massive stars use the proton-proton chain reaction 2. more massive stars use the CNO bicycle

average person in a dark location can make out between...

2,500-3,000 individual stars

the circumference of the Earth at the equator

24,900 miles -Dividing the circumference by that time means that a spot on the Earth's equator is traveling eastward at 1,040 miles per hour -If you're standing at the equator, that motion is trying to fling you off the planet, which reduces your weight by a tad; by about 0.346% -if you weigh 100 pounds at the pole, you'd only weigh 99.654 pounds at the equator

Scientists often use different words for ideas with different levels of acceptance. When an idea is new, it is often termed a hypothesis. For example, Mars is a small planet whose weak gravity allows it to hold only a thin atmosphere, and liquid water cannot exist at the low pressures found at the Martian surface. After seeing what seemed to be dry river beds, deltas, and other evidence of past running water on Mars, some scientists developed the hypothesis that Mars' gravity is sufficiently strong that the planet had lost its atmosphere only slowly, and that at some time in the past it had been more Earth-like, with rain, rivers, lakes, and perhaps even oceans. Many other scientists went to work attempting to disprove the hypothesis. Computer models calculated the loss rate of the early atmosphere, new spacecraft further explored the planet. Much of the new evidence was consistent with the hypothesis; more channels were discovered, a relict shoreline for the hypothesized ocean was located. But, as is frequent in science, not all the new evidence fit. Channels were not widespread, but restricted to certain areas. Permafrost, frozen groundwater, was found to be common. So the hypothesis was modified. Perhaps the channels really were carved by running water, but instead of falling as rain, perhaps the water was produced when permafrost was melted by volcanic eruption or by asteroid impact. Today the idea still has the status of a hypothesis, but is gaining wider acceptance in the scientific community.

A good scientific hypothesis should be consistent with most of our established ideas, should offer predictions so that it can be tested, and should be falsifiable (that is, capable of being disproven). The most attractive hypothesis is worthless to science if it offers no way for us to evaluate its validity by attempting to disprove it.

Plato (428 BC to 347 BC):

A philosopher who argued for the power of logic in trying to understand the nature of the universe. He founded the Academy, the Western world's first institution of higher learning. Two of his ideas influenced astronomy, but would later create problems for Renaissance astronomers. One was his idea of forms, which (and this is a gross oversimplification), said that things here on Earth are imperfect and subject to change, but that there exists an ideal realm (which came to be identified with the heavens) in which all things are perfect and unchangeable. The second came from his writings about the regular geometric shapes (shapes with all sides equal), where he argued that the more sides a regular figure has, the more perfect it is. This lead him to conclude that the circle was the most perfect geometric figure. A consequence of these two ideas is that all things in the heavens are perfect, and must therefore move in circular paths. He challenged his students to find a way to explain the retrograde motion of planets using only regular, circular motions.

Eudoxus of Cnidus (390 BC to 337 BC):

A student of Plato's at the Academy, he attempted to explain retrograde motion using nested spheres.

Anaxagoras (499 BC to 428 BC):

A student of the Pythagorean School who first explained the cause of eclipses. He provided additional support for the spherical shape of the earth by pointing out that the shadow of the earth on the moon during a lunar eclipse was always the arc of a circle. The only geometrical figure that always casts a circular shadow is a sphere

Which is longer? -A sidereal month -A synodic month

A synodic month

Brightest star in Taurus:

Aldebaran (Alpha Tauri)

Claudius Ptolemy (120 AD to 160 AD):

Another scholar associated with the Alexandrian Library. He produced a 13 volume work (The Mathematical Collection) combining and refining the works of all before. The work was translated into Arabic by Arabian astronomers shortly before the destruction of the Library. This translation is the only copy of Ptolemy's work to survive to modern times. The Arabs were so impressed with Ptolemy's work that they renamed it al-Megiste (The Greatest). Subsequent English translations made it The Almagest. Because of this work, geocentric models of the Solar System are referred to as "Ptolemaic". The model he describes is geocentric, and uses circular orbits called deferents. Planets don't move directly on the deferents, but instead move around smaller circles called epicycles whose centers move around the deferents. His model was so successful that it continued to be used for more than a millennium, until the time of Copernicus.

During a lunar eclipse, the Moon passes through the Earth's shadow. (this can only happen during a full moon) During a full lunar eclipse, all of the Moon is in the Earth's umbra During a partial lunar eclipse, only part of the Moon is in the umbra

Any spherical object illuminated by another spherical object casts a two-part shadow; -an inner cone called the umbra (Gr. shade) in which the light source is completely blocked, -an outer cone called the penumbra (Gr. next to shade) in which the light source is partially blocked

Named group of stars that are not constellation is called

Asterisms

If we didn't correct our calendar for this, each equinox and solstice date would slowly drift around the calendar, ending up back on the same date after 25,772 years. This is what causes the twenty minute difference in the lengths of the sidereal and tropical years.

Astrological sun signs are based on when the Sun was in particular constellations in Babylonian times, back when their were only twelve constellations in the zodiac Back then, astrological sun signs and astronomical constellations coincided

the dimmest zodiac constellation

Cancer (has less than 24 naked-eye stars

the Great Temple at Karnak in Egypt had an aisle aligned with the rising point of a bright star on a particular date, but the temple was in use for centuries, and precession slowly messed up the alignment

Centuries later, the aisle was extended, and extended again several centuries after that. Today the aisle has slight doglegs in it illustrating the slow precession

The Sun, of course, is a star, a ball of mostly hydrogen and helium gas. It's roughly 3/4 hydrogen, 1/4 helium, and a couple percent everything else, all hot enough to be vaporized. It's a fairly typical star. If you look at any property of stars; mass, brightness, temperature, et c., the Sun usually sits in the middle of the range for each property. The Sun appears so much brighter than the other stars only because it is much closer to us. Using travel time for light as a unit of measure for distance, the Sun is a little over 8 light-minutes from Earth and the next star is over 4 light-years from Earth. It's about 109 times the diameter of the Earth, 333,000 times the Earth's mass, and 1,300,000 times the volume of the Earth. As are all stars, it's powered by nucelar fusion. Our Sun is currently using the first of the two nuclear reactions it will use, the fusion of hydrogen into helium. In about seven billion years it will have used up the hydrogen in its core, and will shift to a second reaction fusing helium into carbon abd oxygen. At that time it will swell into a red giant, engulfing the Earth, but that's the subject of later chapters in the AST 104 class. The interior of the Sun consists of three layers; the core, the radative transfer zone, and the convective zone. The Sun's atmosphere consists of two layers, the chromosphere and the corona/solar wind. The visible surface of the Sun, the boundary between the convective zone and the chromosphere, is called the phtosphere. You may ignore the other boundary mentioned in the image above, the tachocline. -----The Core------- All the Sun's power is produced here by the thermonuclear fusion of four 1H nuclei into one 4He nucleus, with the emission of neutrinos and gamma rays; the gamma rays eventually lose energy on their way out of the Sun, becoming the light and heat we receive. For most of human history we mistakenly assumed that the Sun was on fire, since fire was the only thing we knew that was hot and bright like the Sun. The history of how we learned otherwise is an interesting one, involving the English conquest of Scotland and the finanacial woes of the Scottish brewing industry, but by the late 1800s it was clear that the Sun was not powered by chemical combustion (burning), else it would have burned out within recorded history. When radioactivity was discovered, and was seen to produce a million times more heat per mass than combustion, people thought for a few years that perhaps it was the source of the Sun's power. But spectroscopy showed that the three most common radioactive elements, potassium*, uranium, and thorium, were simply not present in sufficient quantities to power the Sun. When the nuclear fission of uranium and thorium was discovered, and found to emit 10 times the energy of radioactive decay, it was at first suspected of being the Sun's power source, but there's just not enough uranium and thorium in the Sun to account for its power output. Not until the discovery of nuclear fusion was the source of the Sun's power understood. Before we can discuss fusion in detail, we need to discuss the concept of isotopes that was introduced in Chapter 4 of the textbook. You likely already learned in earlier science classes that its the number of protons that defines an atom as being a particular chemical element; any atom with one proton is hydrogen, all helium atoms have two protons, et c.. The number of protons is called the atomic number, and defines an element's place on the periodic table. But atoms of the same chemical element can differe in their numbers of neutrons; atoms that do are called isotopes of that element. There are three isotopes of hydrogen; they each have one proton, but they have either no neutrons, one neutron, or two neutrons. Isotopes are designated by their mass number, a superscript number to the upper left of the chemical symbol, a number that represents the total number of particles in the nucleus. So, for example, 1H has one proton, 2H has one proton and one neutron, and 3H has one proton and two neutrons. Since the chemical symbol tells you how many protons an atom has, you can subtract that number from the mass number to get the number of neutrons. Helium has two isotopes, 3He and 4He. When we talk about isotopes, we say the name of the element first, then the mass number; 12C is called "carbon 12". Most isotopes don't have names, but those of hydrogen are called protium, deuterium, and tritium. Some isotopes are unstable; their nucleus tends to either come apart, emit high-energy photons, or both. We call these nuclei radioactive. It's impossible to predict when a particular radioactive nucelus will decay, but we can say what the average decay time of a bunch of them would be, the half-life. Of the hydrogen and helium nuclei we've mentioned, all are stable except 3H, tritium, which has a half-life of 12.5 years. So, if I start with a bunch of tritium, after 12.5 years half of those nuclei will have decayed. After another 12.5 years, half of the remaining half will have decayed, so I'll have 1/4 of what I started with. After three half-lives, 1/8, et c.. The other fact we need to know is that of the three hydrogen isotopes, 1H is the most common in nature, while 3He is the most common helium isotope. Now we can discuss the thermonuclear fusion of H into He in our Sun. Fusion means joing together. Nuclear fusion means we are joining together atomic nuclei; in this case, four 1Hs fusing together to make one 4He. But the odds of four 1Hs all coming together at the exact same time, and at the correct angles and speeds to fuse, are quite small; it probably happens in the Sun only once a year or so. Instead, fusion in the Sun takes place via a chain of nuclear reactions. And there's another problem with fusion. Atomic nuclei have positive charges, and things with like electrical charges repel each other. To overcome the repulsion and get atomic nuclei to fuse, we have to get them moving really fast. One way to do this is to get them really hot. Recall that temperature is a measure of how fast particles are moving. We'd need to get hydrogen nuclei up to at least 10,000,000 Kelvin to get them to fuse. On Earth, one way to do that would be to place hydrogen nuclei in the fireball of an atomic bomb, that's how hydrogen fusion bombs work. The nuclear reactions that power the Sun are called thermonuclear fusion reactions; the "thermo" refers to the high heat necessary. The intense pressure in the core of the Sun provides that heat. here are 17 possible fusion reaction chains that fuse four 1Hs into a 4He. We've done them all on the scale of atoms in cyclotrons, and done them on the scale of pounds in hydrogen bombs, but only two of these chain reactions occur in stars; the three-step proton-proton chain (known as the p-p chain), and the seven-step CNO bicycle (pronounced bi-cycle, not bi-sickle). Our Sun gets about 80% of its energy from the p-p chain, so in this chapter we shall ignore the CNO bicycle, saving it for later chapters in AST 104 where we discuss the stars in which it dominates. Below are the three reactions of the p-p chain. You'll need to memorize and understand them. 1H + 1H —› 2H + positron + neutrino In this first reaction of the p-p chain, two 1Hs (two protons) fuse to make a 2H, with the release of a positron and a neutrino. Obviously this involves turning a proton into a neutron. That can be done using the weak nuclear force, but something must carry away the positive charge on the proton, since the neutron is neutral. The problem is that a neutron is almost as massive as a proton, which at the time this reaction was being explored was the smallest known particle with a positive charge. Physicist Paul Dirac predicted that there must exist a particle with the small mass of an electron, but with a positive charge. Today we call this particle the positron, and here it carries away the positive charge from one of the protons. The positron is antimatter** to the electron, so when it meets an electron (which it does almost instantaneously), the two of them annihilate each other, converting their combined masses into energy through E=mc2, energy that is released as two gamma rays, the highest-energy form of light. I'm not going to go into the particle physics involved, but there's another nuclear property that protons possess, but neutrons and positrons don't, so yet another particle was predicted to carry it away. That particle must have no charge, and either no or very little mass. Enrico Fermi named it the neutrino, "little neutral one"; it was decades before its existence was confirmed. 1H + 2H —› 3He + gamma rays The other two reactions in the p-p chain are much more straighforward, as no subatomic particles change identities, they just get rearranged. Here in the second reaction, a proton (1H) merges with the proton and neutron of a 2H. The result of course is a nucleus with two protons and a neutron, 3He. Because the collision is lopsided, with the 1H outmassing the 2H, the resulting 3He is an oscillating ball. This energy of oscillation will be shed as either 2 or three gamma rays, depending on the angle of the collision. 3He + 3He —› 4He + 1H + 1H Here two 3He's merge to form a 4He. If you count up the particles, you'll find that there are two protons (two 1Hs) left over, which emerge at high speeds in opposite directions. So, ultimately the energy of the Sun comes mostly from the gamma rays released by the annilation of the positron in the first reaction, the gamma rays from the second reaction, and the kinetic energy of the protons from the third reaction. But what we get from the Sun is visible light, not gamma rays. The transformation of high-energy gamma ray photons into lower-energy visible light photons takes place in the Sun's other layers. ----------Radioactive Transfer Zone------ This is the zone above the core; it's often abbreviated as the RTZ. It's below 10,000,000 Kelvin here, so no nuclear fusion takes place. But it's still hot enough that all the atoms are completely ionized, meaning that all of their electrons are ripped off. We learned in Chapter 5 that when light gets absorbed, it gets absorbed by electrons in orbit around atomic nuclei, causing the electrons to move farther from the nucleus. Here there are no electrons orbiting atomic nuclei, so light absorption isn't possible. When a substance absorbs light, we call it opaque. Window glass does not absorb light; we call it transparent - light can pass through it in a straight line, and we can make out the image of what's on the other side. The radiative transfer zone is neither opaque nor transparent, it's translucent, like a frosted shower door. Light can go through it, but the atomic nuclei are so tightly packed that the light can't get very far before bouncing off a nucleus at some random angle. So if we could magially float in the radiative transfer zone, we could get a clear view down to the core, instead, we would seem to be hanging in a glowing fog. As a matter of fact, the density in the radiative transfer zone is so high that a photon coming up from the core spends a huge amount of time just bouncing around in random directions. Even though photons travel at the speed of light, it takes the average photon tens of thousands of years to make it through the RTZ. The temperature id hotter closer to the core, so as a photon gets to the outer part of the RTZ it's bouncing off slower nuclei. The photon loses energy to these nuclei, so although it left the core as a gamma ray photon, by the time it gets to the outer part of the RTZ it's an X-ray photon. -----Convective Zone---------- This zone goes from the RTZ to the surface, and it's cooler than the RTZ. It's sufficiently cool that electrons can orbit in atoms, so light absorption is possible, making this zone opaque - light cannot pass through it. So how does the energy get through to the Sun's surface? The X-ray light from below gets absorbed by gasses at the bottom of the convective zone, making the gas hotter. The hot gas expands and, becoming more buoyant, rises through the convective zone to the Sun's surface. There with nothing more than the transparent gasses of the Sun's atmosphere above it, the hot gas can shed it's energy as light. Since it has cooled on the way up, it now emits visible light rather than X-ray light. After the energy is released, the now-cool gas can sink back down, to be reheated at the bottom and start the cycle over again. Since the rising of hot fluids and the sinking of cold fluids is called convection, this layer is called the convective zone, or CZ. Coming through this zone, the energy is no longer a photon travelling at the speed of light; it's now a blob of hot gas slowly rising through the surrounding gas as part of a convection cell. This takes hundreds of thousands of years. Once the blob of hot gas reaches the surface and emits its energy as visible light, it will only take that light about 8 1/2 minutes to travel the 93,000,000 miles (1 AU) to the Earth, but the sunlight that reaches us today left the core of the Sun hundreds of thousands of years ago; it's antique sunlight! --------The Photosphere--(sunflower) This is not so much a layer, as the visible surface of the Sun, the top of the convective zone. There are two sorts of feautres seen on the Sun's surface. The tops of the individual convection cells appear as bright yellow blobs thaat cool within a few minutes to dim orange (remember Stefan's and Wien's law?) and sink back down; you can see many of them in the outskirts of the picture below. And then there are the sunspots, like the one seen in the middle of the picture. Sunspots typically have a cool, dark inner core called the umbra that glows a deep orange (this one is underexposed in the photo, so it looks black), surrounded by a radially-streaked penumbra. The one below is larger than Texas, but smaller than the US. Large ones can be 15 times the size of the Earth. We'll learn more about them on the next page in the section on solar activity. -----Chromosphere-----(eclipse w/red) Since the layers of the Sun's atmosphere are transparent, they don't show up in normal photos. Both layers are hot enough to glow, but their light is dim compared to that from the surface of the Sun beneath them. The layer closest to the surface is the chromosphere. It is at just the right temperature that its hydrogen gas emits the red emission line you saw in the hydrogen emission spectrum in Chapter 5, the one called the H-alpha line. The upper surface of the chromosphere is irregular, with a spiky upper surface. The first person to see this was Italian, so the spikes are called spicules. You can see them in the image below, poking out around the edge of the Moon during a solar eclipse. Spicules are really fountains of gas thrown up as convections cells break onto the surface of the Sun; they rise up several thousand miles over a few minutes, then collapse back down again. Besides seeing the spicules during a solar eclipse, the other way to see the chromosphere is to use a specialized, expensive, narrow bandpass filter that only allows that one shade of red H-alpha light through. ---The Corona/Solar wind---(angelic) The outer layer of the Sun's atmosphere consists of gasses boiling off the surface of the Sun and heading out into space. They are heated to temperatures over a million degrees by poorly-understood magnetic effects, but the gasses are very thin, so the overall glow is quite faint. It can only be seen by blocking out the light from the photosphere, either by the Moon during a solar eclipse, or by a disk placed in a telescope. This glowing exhalation of gasses streaming off the surface of the Sun is called the corona, because ancient Greeks and Romans thought it resembled a crown around the Sun during a total eclipse. (The word "corona" is Latin for "crown"; think of the logo on the eponymous beer bottle.) You can see the corona in the photo below. As the gasses cool, the glow fades, and we change the name from the corona to the solar wind. As the solar wind, the gasses continue out past the planets until they meet the corresponding gasses from nearby stars, so all the planets in our Solar system are enveloped on the solar wind. -----Notes----- * One of the naturally-occurring isotopes of potassium, 40K, is radioactive - a gamma-ray emitter. Potassium is essential for life, as our nerves won't function without it, so it's ironic that this esential nutrient nay be responsible for 1/8 to 1/4 of all cancers. Bananas are a good source of essential potassium, but they are not the most radioactive food we eat; that would be Brazil nuts. The Brazil nut genus, Bertholletia, has an enzyme which serves to concentrate barium from the soil for use by some other enzymes, but it can't distinguish barium from radium, and so ends up concentrating radioactve radium, which is a decay product of naturally-occurring uranium. So Brazil nuts are typically about 1000 times as radioactive as other foods. ** Antimatter is not a substance, it's a relationship between two subatomic particles. When two particles share all their nuclear properties except one, and when that one property is opposite in the two particles, they are said to be antimatter to each other. If they meet, they annihilate each other, turning their masses into gamma rays.

Ch 14 The sun (structure & operation)

Astronomers rarely have the luxury of hands-on experimentation. True, we have about 800 pounds of Moon rocks, a couple of hundred Mars rocks, some gas atoms from the Sun, and tens of thousands of asteroid pieces. We have flown robotic spacecraft to land on Mars, Venus, and an asteroid; and to fly past all the eight major planets in our Solar system. But the only material we have from outside the Solar system is a collection of diamonds so small that if bacteria wore engagement rings, they'd be the right size. These diamonds formed either in the atmosphere of a large star, or in the explosion of a large star, shortly before our Solar system formed, but we can't even tell you which star. Other than that, the only thing we get from stars is light. And yet, point to any star you can see with the unaided eye, and astronomers can tell you that star's brightness, surface temperature, distance, speed of motion, direction of motion, rotation rate, chemical composition, magnetic field strength, surface pressure, etc. All of these things they learn from the study of the star's light. (Actually there's even more they know. They can tell the temperature, pressure, and chemical composition at any depth within the star, the subatomic details of the nuclear reactions that power the star, the expected lifetime, and sometimes even the age. These don't come directly from the light, but by application of mathematical models which use the information of the light as input data.) The image below shows two star clusters in Gemini; M35 (the larger one in the upper left) and NGC2158 (smaller, lower right). After the next two chapters, you'll be able to instantly spot the coolest star in the picture, and tell me that the stars in one of the clusters are significantly hotter than those in the other. By the time you finish AST 104, you'll be able to tell that there is a significant age difference between the two, and that the older one may indeed be older than our Milky Way galaxy (of which both are members). The speed of light (which scientists abbreviate "c" for "constant), and talked about some of the vast distances light must travel to reach us from astronomical objects. But what is light? Light is the form of electromagnetic radiation our eyes are sensitive to. Electromagnetic radiation includes not only visible light, but also infrared light, ultraviolet light, radio waves, microwaves, X-rays, and gamma rays. This term, "electromagnetic radiation", is the source of much confusion among non-science students, probably because many people associate the word "radiation" with the ionizing radiation given off by radioactive materials or by nuclear reactions. Ionizing radiation occurs in five forms; alpha particles, beta particles, ultraviolet, X-rays, and gamma rays. *alpha particles-high speed helium nuclei *beta particles- high speed electrons *ultraviolet,x-rays, gamma rays are electromagnetic radiation, most forms of electromagnetic radiation are incapable of causing damage by ionization. Radiation is any way energy is transported without the need for a physical connection. Sound waves radiate from a speaker. Light radiates from a light bulb. Electromagnetic (EM) radiation is energy carried as rapidly fluctuating electric and magnetic fields. ---This energy can behave either as a particle or as a wave. --- When it behaves as a particle, we call the particle a photon, and characterize it by the amount of energy it carries. When it behaves as a wave, we describe it using characteristics of a wave, such as the wavelength (the distance between adjacent waves), the frequency (the number of waves which pass a place per second), and the speed (which for electromagnetic radiation is always the same, the speed of light.) Scientists typically designate wavelength with the lower case Greek letter lambda, frequency with either the lower case English "f" or the lowercase Greek nu, and speed with the English "v". Of course, if the wave is a type of electromagnetic radiation, "c" could be used. Much of our work in this course will involve light acting as a wave. It's natural to ask, "What is it that's moving in this wave?" After all, *A water wave consists of water molecules moving in unison. *In a sound wave, molecules of air (or some other medium) move. A water wave could not exist without water, and sound cannot travel in a vacuum. Light can travel in a vacuum, and indeed travels slightly faster there than anywhere else (that bit about the speed of light being constant is only strictly true if the medium it's moving in doesn't change.) So if light can travel where there is nothing, what is it that's waving in these waves? The answer is, nothing. These waves are not the physical path of a moving object, but graphs of the fluctuating strength of electric and magnetic fields as the energy passes. (Electricity and magnetism are inseparably linked, hence the term "electromagnetic".)

Chapeter 5 (Light) Astronomers need to have a good understanding of light, because they lack a fundamental luxury most other scientists have; the ability to get to their subject Wavelength x Frequency = Velocity Frequency = velocity/wavelength

Star Properties: Look up at the stars, just with your eyes. What can you tell about each one? It's immediately obvious that some are brighter than others, and that some have different colours. But that's about it. And yet when you look up any particular star. scientists know a lot more about it. If I Google Betelgeuse and glance at the Wikipedia page for it, I see the star's brightness, colour, speed and direction of motion (including the presence of a bow wave), distance, mass, size, temperature, surface gravity, chemical composition, rotation rate, and age. How do we know these? That's what this chapter's about. At the end of the chapter there are a few other types of information, mostly about variable stars and star clusters. The next three chapters after this one together trace the life cycles of stars, from their nurseries, raw material, and birth through their death, to the various types of stellar corpses, and the various ways they can be reanimated as stellar zombies. Of course, we know that stars are not alive, but the language of personification is too useful not to utilize. --------------------------------------------- Star Properties - Brightness The Hubble Space Telescope photo below looks toward the centre of our Milky Way galaxy, in the direction of Sagittarius. Notice that there's a wide variety of brightnesses amongst the stars. Astronomers have several systems to talk about the brightness of a star. We'll see three of them in this class. (Apparent Magnitude, m) The oldest and simplest system is called apparent magnitude, m. It's a ranking scale first used in Ancient Greece by Hipparchus, and formalized in the mid-1800s. The bright star Vegas in the summer sky is designated as zero magnitude, and fainter stars run down through first through sixth magnitudes. The four stars brighter than Vega, as well as the Sun, Moon, and some planets, are assigned negative apparent magnitudes, and after the invention of the telescope, stars too faint to be see with the naked eye were assigned rankings fainter than 6th magnitude. Today our best telescopes see down to about 30th magnitude. (Absolute Magnitude, M) The problem with the apparent magnitude system is that it doesn't tell us how bright a star actually is. Does a bright star look bright because it really is bright, or because it's very close? Is a dim star dim because it really is dim, or because it's far away. If you have a light meter and a light source, a few minutes experimentation will show you that as a light source gets farther away, the light drops off as the square of the distance; move a light twice as far away and it gets four times fainter, three times farther away makes it nine times fainter, four times farther makes it sixteen times fainter. This effect is called the inverse square law. So if I know the distances to each of several stars, I can use the inverse-square law to calculate how bright they would appear if they were all at a particular reference distance of 32.6 light-years. We'll see why such a peculiar reference distance was chosen in the next page about distance. The calculated brightness of any star if it were moved to that reference distance is called absolute magnitude, M. (Luminosity, L) So apparent magnitude tells me how bright a star looks. Absolute magnitude tells me how bright a star is, but the numbers are awkward - the apparent magnitude a star would have at a reference distance. Classical astronomers like absolute magnitude. The rest of us use luminosity, L, which is simply the absolute brightness of a star divided by that of the Sun. So if a star is ten times brighter than the Sun, it has a luminosity of 10. (The units are called "solar brightness units".) Of course, in order to calculate either a star's absolute magnitude or its luminosity, I need its distance. How we get that is the subject of the next page. -------------------------------------------- Star Properties - Distance We have many methods to measure distances to astronomical objects. The most accurate ones only work for nearby objects; the farther out we go, the less accurate the method. We'll meet three of the methods in this chapter; the first method we'll discuss is stellar parallax. (Stellar Parallax) Close one eye, hold your finger up at arm's length, and note what's behind it. Now, leaving your finger and head still, switch eyes; shift your view to the other eye. It appears your finger moved. Of course your finger didn't move, but shifting your viewpoint (from one eye to the other) causes a nearby object (your finger) to appear to shift against a more distant backdrop. This effect is called parallax, and the amount of shift is called the parallax shift. Now try the experiment again, but instead of holding your finger at arm's length, bring it halfway in toward your eye. What happened to the amount of shift? That's right, it increased. The closer a nearby object is, the greater the parallax shift it shows when viewed from two different viewpoints. Of course, the viewpoints have to be at right angles to the line-of-sight to the object, just as a line connecting your eyes is at right angles to a line to your finger in this experiment. With a little bit of junior-high geometry, you can see that if I know the spacing between my eyes, and the angle of the parallax shift of a nearby object against the background, I can calculate the distance to the nearby object. But if you stand on the Charleston campus, and try to measure the distance to the Stratosphere tower this way by sighting against Frenchman Mountain in the background; it won't work. Your eyes are so close together that the parallax shift is too small to be seen; you'd need a bigger baseline. You could take sightings from 100 yards apart, and that would work. Remember from Chapter 3 that the Ancient Greeks measure the distance to the Moon by sighting the parallax shift of the Moon against the backdrop of the stars as seen from Greece and Spain. The first object beyond the Moon to have its distance measured was Venus, using the limb of the Sun as the backdrop during transits of Venus. To measure the distance to nearby stars we can use the two sides of the Earth's orbit as a backdrop, but even then the parallax shift is tiny. Telescopes only got good enough in 1838, and even today most stars you can see with the unaided eye are too far away to use stellar parallax to measure their distance. Seeing through the Earth's atmosphere blurs star images (remember Chapter 6), and means that from observatories on Earth, we can use stellar parallax to measure the distances to stars out to 150-or-so light years. Remember that from Chapter 1 that our Milky Way galaxy is 100,000 light years across! The Hipparcos satellite, since it's above the atmosphere and not limited by seeing, measured distances out to 1,600 light years, while the European Space Agency (ESA) Gaia satellite can measure the distance of a few really bright stars up to 10,000 light years out. That still leaves lots of stars we can see with the unaided eye, but can't use stellar parallax to measure their distance. We'll learn other distance-measuring methods as we go through the rest of the semester. ------------------------------------------- Star Properties - Temperature Just as for distance, we also have many methods to measure temperatures of stars. The easiest are often less accurate, while the more accurate methods require more sophisticated equipment. (Colour) Recall Wien's Law from Chapter 5; the hotter a glowing object is, the shorter the wavelength of light its spectrum peaks at; blue stars are hot, red stars are cooler. You can see in the ternary graph below that normal stars range from about 1,000 °C to over 20,000 °C. Given the different sensitivities of the human eye to different colours, if you step outside and see a star looking red, that's probably below 3,000 K. Stars that appear yellow (like our sun) are between 4,500 K and 6,500 K, while stars that appear blue are over 8,000 K. (Colour Index) With a light meter and some colour filters, you can get more accurate. The difference between the brightness of a star at one wavelength minus that at a shorter wavelength is called the colour index. A widely-used colour index is the B-V index, the brightness through a blue filter minus that through a yellow-green filter. With this system you might tell the temperature of a star to within 100 K. Colour index methods are sometimes called photometric methods. (Plank Curves) Recall from Chapter 5 that the peak of the Planck curve shifts with temperature according to Wien's and Stefan's Laws. You need a spectrometer to spread the light, and some way to record it, but spectrometers are available for backyard astronomers these days, and a digital camera will record the spectrum. The temperature accuracy's not much better than the B-V method, but you can also get to see absorption lines. (Recall that 90% of stars have absorption lines in their spectra.) (Spectral Lines) Which brings us to the most accurate method. In Chapter 5 we learned that absorption lines are caused by electrons absorbing energy and moving to larger orbits (higher energy levels). Which level the electrons are in depends on the available energy â€" on the star's temperature. At different temperatures, different spectral lines from different chemical elements appear. Studies of which spectral lines are present can determine the temperature of many stars to within 10 K. ---------------------------------------- Star Properties - Classification One of the most impressive stories in science is that of the women who figured out the stars. (Purpose of Classification) Classification can serve many purposes, but one important thing scientists use it for is to help us when we are clueless. Before we see how it helped us understand stars, let's look at two more familiar examples from high-school science classes, the biological classification schemes for animals and plants. A good classification scheme should be based on as few properties as feasible, but it's important to pick the right properties. They should correspond to natural groups in the range of things being classified; if they do, the resulting groups will illustrate new relationships we didn't know existed. Consider animals. Is colour a good property to base a classification on? Probably not; a brown squirrel, a brown fish, a brown bird, and a brown frog would all end up classed together despite their obvious differences. Mass? Again, songbirds, frogs, mice, and fish would all end up together. It took a lot of observation and thought before biologists settled on the properties they use; type of skin covering, how an animal bears its young, and whether it's warm- or cold-blooded (although that criterion is no longer as useful as it once was, with the realization that birds some dinosaurs were warm-blooded and that birds are dinosaurs). If an animal has fur, bears its young live, and is warm-blooded, it's a mammal. If it has feathers, is warm-blooded, and lays eggs, it's a bird. If it has scales, lays eggs, and is cold-blooded, it's a reptile. If it has moist skin, lays eggs, and is cold-blooded, it's an amphibian. How do we know those three properties are better choices than colour or mass? Because the resulting groups have thousands of other properties in common, properties that were not used to define the group, properties such as skeletal and chemical differences. This tells us the groups truly exist in nature; we didn't just make them up. No classification scheme is perfect. What about a creature that has fur and is warm-blooded, but lays eggs? Such a creature, like the platypus, doesn't fit readily into the scheme. (Use of other properties like the skeletal and chemical differences mentioned leads to the classification of the platypus and the other four monotremes as mammals.) Consider flowering plants. Should we use flower colour? A yellow rose and a sunflower? After much observation and deliberation again, biologists have settled on just one property to classify flowering plants; the shape of the sex organ. What is the sex organ of a flowering plant? Here's a hint; we sever them and present them to other people as tokens of our affection. That's right; flowers. (Classifications of Stars) Now let's consider stars. At the turn of the 20th century, we didn't know what stars were. Most people assumed they were balls of rock like Earth, only much bigger and hotter. A popular idea at the time was that sunspots were clouds that blocked the light from the glowing surface beneath. But that was just one idea; there were others. So what do you do when you're a scientist, and you really don't understand your subject? You collect as much data as you can, since you don't know which data will prove important. And you look for patterns, a classification scheme that might help point out ways in which certain parts of your subject are similar or different. Recall from Chapter 2 the Henry Draper Catalog, in which was collected any measurement made about each star. This work was done at Harvard University. Enter Edward Charles Pickering and the Harvard Computers. "Computer" at the time was a job title, mostly used in the insurance industry for the clerks who complied actuarial tables. (Think Monty Python's "Crimson Permanent Assurance".) Pickering was the director of the Harvard Observatory, and under his direction, employees called computers were photographing the night sky with telescopes, measuring the position, brightness, and colour of stars, and fitting a prism over the telescope to collect spectra. Data was coming in faster than it could be processed and cataloged, and this wasn't helped by the fact that the young men employed as computers were more interested in other things than their work. As a physicist rather than an astronomer, Pickering was convinced that one day the spectra of stars would be understood, and that the enormous library of spectra they were collecting would have scientific value. From the 1880s to the 1920s, a series of famous women worked as computers and made huge contributions to astronomy. (Williamina Paton Fleming) Enter the first of the famous Harvard Computers, Williamina Paton Fleming née Stevens. Born in Scotland, she and her new husband moved to Boston, but her husband abandoned her when he learned she was pregnant. Pickering's wife Elizabeth hired her as a household maid, and Pickering was known to upbraid slacker computers with, "My Scottish maid could do better!" Elizabeth recognized Williamina's skill at organization, and suggested to her husband that he hire her at the observatory. At the time, women were not allowed to attend US universities; women could attend "normal schools" where they could learn to be teachers, or they could attend special women's colleges such as Radcliffe. But Pickering trained Fleming informally in the skills needed for the observatory job. She was not allowed to take photographs and spectra in the observatory at night, where she might prove to be a distraction to the men working there, but working during the day, she developed a new classification scheme for the stellar spectra in the Henry Draper Catalog, an alphabetical scheme A through O based on the intensity of the hydrogen absorption line, with A-type stars having the most intense hydrogen lines, and O-types having none. The assumption at the time was that this was a measure of how much hydrogen each star had, though we'll soon see this turned out to be wrong. Fleming organized the photograph and spectral collections, and classified thousands of stars, the majority of stars in the Henry Draper Catalog. (She also discovered the class of stars known as white dwarfs, and the Horsehead nebula.) (Antonia Caetana ) Antonia Caetana de Paiva Pereira Maury was Henry Draper's niece, and another of the Harvard Computers. Antonia Maury expanded Williamina Fleming's classification scheme to include spectral line width, and rearranged the order of the letters based on temperature instead of the intensity of the hydrogen absorption line, which resulted in some duplication in which different letters represented stars of the same temperature. (Spectral Type Classification) (Annie Jump Cannon) Enter Annie Jump Cannon, daughter of Delaware state senator Wilson Cannon and his second wife Mary Jump, who spent many hours with Annie in their attic with a small telescope and encouraged Annie's love of astronomy. Deafened by a bout of scarlet fever (a strep infection that has spread to the blood), as a Harvard Computer, Annie became famous for the speed and accuracy with which she could classify stellar spectra. She could classify five spectra per minute, netting over a third of a million in her lifetime. She rearranged and merged Fleming's and Maury's classification schemes into today's spectral type classification, which is arranged in temperature order, but is no longer alphabetical. The scheme runs OBAFGKM, from the hottest blue-white O-type stars to the coolest red M-types. You'll need to memorize this order; on a quiz or exam you will need to know which of two types is hotter, say, B or G. Our Sun is a G-type star. Each spectral type can also be subdivided 0 through 9, with 0 being the hottest. (What Are Stars Made Of?) (Cecilia) At this time the assumption was that stars were rocky worlds like Earth, but were hot enough that their atmospheres were glowing. The person who figured out what stars are made of was another Harvard Computer, Cecilia Helena Payne, who later married fellow astronomer Sergei Gaposhkin and became Cecilia Payne-Gaposhkin. She was the first person to receive a PhD in astronomy from Radcliffe. She later became the first female full professor at Harvard, and the first department chair there when she headed the astronomy department. Cecilia studied at England's Cambridge University at a time when women were allowed to attend classes, but could formally enroll as students, nor be granted degrees. During her third year there in 1921, a proposal was brought to the University Council of the Senate that women be granted membership in the university, but the vote went against the proposal; women were to be granted the "titles of the degrees, but not the degrees themselves." Even this compromised so enraged the male students that they rioted, attempting to use coal carts to crash the gates of the women's dorm where Cecilia watched from an upstairs window. While at Cambridge, Cecilia studied under Niels Bohr, who figured out how electrons move in atoms (the key to spectroscopy), and under Ernest Rutherford, who discovered the existence of the atomic nucleus. Convinced by several faculty that nobody in England at the time would hire a female astronomer, she was advised that with graduation approaching, she should contact the Harvard Observatory. (Meghnad Saha) Indian physicist Meghnad Saha (whose grandson later took AST 104 from me here in Las Vegas). Saha was studying the spectrum of the simplest possible flame, the burning of hydrogen with oxygen. He varied the ratios of the two gasses and realized that the intensity of the hydrogen line didn't vary directly with the amount of hydrogen. There was an optimum mixture that produced the most intense hydrogen spectral lines. Away from that optimum, with either too much or too little hydrogen, the flame was cooler and the spectral lines were weaker. Saha showed that at low temperatures the electrons lacked energy to make the transition resulting in the spectral line, while at high temperatures more atoms were ionized, with no electrons available. He presented a mathematical analysis of the relationship between the spectral line intensity, electron energy, ionization, and temperature. He suggested that this could apply to stars, but had no access to stellar spectra. As Cecilia contemplated this, she realized that this could be why the hydrogen spectral line intensity of stars peaked at intermediate temperatures. This became her PhD research project; she developed a mathematical treatment relating spectral line intensity to the temperature-driven ionization state of different chemical elements. A consequence of this work was that she came to realize that all stars have essentially the same amount of hydrogen. They are not giant rocky objects like Earth, but balls of gas that are roughly 3/4 hydrogen. She's the person who figured out what stars are. Her work flew in the face of the accepted idea of the day, and the famous Princeton astronomer Henry Norris Russell (whom we shall soon meet) persuaded her to describe her result as "spurious". It proved correct, however, and later another famous astronomer, Otto Struve, called her work "the most brilliant PhD thesis ever written in astronomy". We'll meet another of the Harvard Computers, Henrietta Swan Leavitt, later in this chapter. Although Cecilia Payne explained the connection between Annie Jump Cannon's temperature-based spectral type classification scheme and the intensity of the hydrogen spectral lines, and showed that stars are balls of gas that are mostly hydrogen, temperature alone did not make a good classification scheme for stars. While it was true that most O-type stars had many other properties in common, and many M-type stars did as well, stars in the middle of the spectral type scheme might have widely different properties. Stars were not going to be like plants, classifiable on only one property. They would turn out to be more like animals, needing multiple properties to make a useful classification scheme. That's the subject of our next section, the H-R Diagram. -------------------------------------------- Star Properties - H-R Diagram So temperature alone wasn't sufficient to classify stars. Two men independently found that combining temperature with another property divided stars into groups that made sense. But the choice of the other property, brightness, wasn't obvious. A fter all, Stefan's law already said that the hotter a glowing object is, the brighter it should glow, so if all stars were plotted on a graph of temperature versus brightness, they should all fall along one line. But it turned out they don't. (The H-R Diagram) Danish astronomer Ejnar Hertzsprung and the famous American astronomer Henry Norris Russell both submitted papers about this to Nature in the same month in 1913, so they get joint credit. Hertzsprung's was postmarked first, so he gets top billing. A schematic form of the diagram is shown below; there are others in your textbook. Although the specific variables plotted can vary, the x-axis is some measure of temperature. Since spectral type (OBAFGKM) runs from hot to cold, the x-axis is usually plotted from hot to cold, contrary to usual mathematical practice. Don't let that catch you out. The y-axis plots some measure of brightness, either luminosity or absolute magnitude. (Apparent magnitude won't work. Do you understand why not?) Roughly 90% of all stars do roughly follow Stefan's law give or take a few wiggles, and lie on a sigmoidal curve down the middle of the graph. This area is called the main sequence, and stars that fall in this area are known as main sequence stars, or MS stars. Our Sun is a MS star. The main sequence ranges from small, dim, red stars on the cool and dim end to large, bright, blue stars on the hot and bright end. The second diagram below shows the range of sizes and colours of main sequence stars. (look at the image)***Hertzsprung Another group of stars are brighter than their temperature would suggest they should be from Stefan's law; these are the giants. If you go back to Chapter 5 and review Stefan's law, you'll see that it actually talks about how the amount of light emitted per unit area depends on temperature. So I can increase the amount of light a star puts out by increasing the temperature, but I can also increase it by increasing the surface area â€" by making the star bigger. Giant stars are roughly a hundred times larger than our sun; if our sun were a giant, Earth's orbit would be inside it. Even brighter overall are the supergiants, which manage to be incredibly bright by being incredibly big, the size of our solar system. Tucked down in the lower left corner, hot and dim, are the white dwarfs, which manage to be dim by being very small, roughly the size of Earth. (look at image = 7 circles) The image below shows the relative sizes and colours of main sequence stars. So by classifying stars on two properties, temperature and brightness, we've seen them fall into four distinct groups, with most of them being main sequence stars, but a few of them being giants, supergiants, or white dwarfs. Have we picked good properties? If so, the four groups will be meaningful, and will each have other things in common. To jump ahead, we'll see in the next three chapters that the answer is yes, these are valid natural groups. What we'll learn in the next three chapters is that all stars begin as MS stars, then go on to become giants. After that, some will become supergiants and then explode in the giant explosions we call supernovae. Others will lose their outer layers as colourful shells of gas known as planetary nebulae, then their exposed cores will be known as white dwarfs. Stars are powered by nuclear fusion, and these changes are caused by shifts from one fuel to another. But we're getting ahead of ourselves; we have a few more stellar properties to discuss. --------------------------------------------- Star Properties - Luminosity Class & Distance (USE H-R diagram) We haven't yet talked about how to determine the size of a star; there's another property we'll need first, the luminosity class. And it turns out that knowing a star's luminosity class will give us a second way to determine a star's distance, a way that isn't as accurate as stellar parallax but that can be used for stars much farther away, indeed, for most of the stars in our galaxy and even some of the bright ones in neighbouring galaxies. We'll need an H-R diagram for this. You see a star. It's orange, which gives you a rough idea of its temperature, but you need more accuracy. Do you remember how to do that? If not, maybe you'd better refresh yourself on it before the next exam. You get out your light meter, and your B and V filters, measure the brightness, and subtract the V reading from the B reading. You get a B-V of 0.85, which according to the x-axis on the H-R diagram above means your star is a K-type star, about a K5. But two photos taken six months apart, from opposite sides of Earth's orbit show it at the same position, so it's too far away to use stellar parallax to determine its distance. Without distance, you have no way of converting the measured apparent magnitude into absolute magnitude through the inverse square law. So on the H-R diagram, your star could be anywhere along a vertical line running up from K5. That means it could be an MS star, a giant, or a supergiant. (But not a white dwarf â€" they don't go over that far to the right.) If you had a way to tell which group it's in, you could read off a range of absolute magnitudes from the y-axis, then use the inverse square law to calculate a distance from the absolute magnitude and your measured apparent magnitude. There is such a way; it's called luminosity class. Think back to Chapter 5 on light. Many things affect the width of spectral lines, but one of them is pressure; the higher the pressure, the wider the spectral line. Light from stars comes from the star's surface. Tiny compact stars have high pressures at their surfaces; swollen fluffy stars have low pressures at their surface. You can see where I'm going with this. Supergiants have really thin spectral lines, giants have thicker lines, and the lines of MS stars are thicker still. There's a scale of line width that uses Roman numerals I through V, and is called luminosity class. So, if my star's spectral line width falls in luminosity class III, I know it's a giant star, plotting roughly where Aldebaran is in the H-R diagram above. That means it has an absolute magnitude around 0, and I can compare that to its apparent magnitude using the inverse square law to get its distance. You can see that if its luminosity class had been a I, it would be a supergiant. Then I wouldn't know its absolute magnitude as accurately â€" it could be anywhere from about -5 to -9. So, I wouldn't be able to calculate its distance as accurately either. So, this distance-determining method isn't always as accurate as stellar parallax, but the advantage is that I can use it for any star I can get a spectrum from. That means most of the stars in our Milky Way galaxy, and some of the brightest ones in a few neighbouring galaxies. Throughout the rest of the semester, we'll see other distance-determining methods, each one successively less accurate, but each able to reach out to greater distances. --------------------------------------------- Star Properties - Mass & Size These two properties really should each get their own page, but I'm placing them together to emphasize that they are NOT the same thing. Just as we tend to confuse rotate and revolve, or mass and weight, so we also have a tendency to mix up mass and size. Mass is how much material something has; size is the space that material takes up. My king-sized pillow has a mass of three pounds, but it's a pretty good size. A rock that same size would have a much greater mass; I doubt I could lift it. (Mass) Recall from Chapter 4 the difference between mass and weight; mass is how much material something has; weight is the pull of gravity on that material. When you weigh yourself on a bathroom scale, you're measuring force â€" the pull of gravity on your mass. Obviously, I can't put a star on a bathroom scale for lots of reasons, but even if I had a giant, heat-proof bathroom scale, it still wouldn't work, 'cause there's no external gravity to pull the star down onto the scale. Sure, the star has its own gravity, but that would pull the scale down into the star â€" Oops! Another way to measure the mass of something is to take advantage of Newton's Second Law of Motion, F=ma. I can push on something with a known force, see what acceleration I get from that, and calculate the mass. (That's really what your bathroom scale is doing. You can think of weight as the acceleration you would be getting from the force of gravity if your bathroom scale weren't in the way...like if you'd stepped off a cliff.) But obviously it's kinda hard to push on a giant ball of gas. But, let's get back to that external gravity idea. We have Newton's Law of Universal Gravitation, which says that the force of gravity between any two objects is equal to the product of their masses divided by the square of the distance between them, times a constant. If two stars are orbiting around each other, the timing of their orbit will give us the force of gravity between them. Then if I can tell how far apart they are, I can use the equation to calculate the product of their masses. That doesn't immediately give me their individual masses, but the balance point that the two orbit around can give me that. If the two have the same mass, they'll orbit around a point halfway between the two; if the ratio of their masses is 9 to 1, the balance point will be 90% of the way toward the more massive star. So, what are the odds of finding two stars orbiting each other? Pretty good, actually. Only 40% of stars are solitary like our sun. We'll see in the next chapter that no star can form by itself; all stars form in star clusters. (We even know which cluster our sun formed in; when you look at the Big Dipper, you're looking at the last remnants of our sun's parent cluster. It was too small to hang on to most of its stars, so many of them have wandered off.) Now, not all of the 60% of non-solitary stars are in pairs; many are in triplets, quadruplets, all the way up to large star clusters. But when we find a pair of stars, we can determine their combined mass, and often their individual masses. The trick is telling when two stars are orbiting each other. Many stars appear close together in the sky, but are not orbiting each other; one will be farther away from us than the other. Such apparent pairs are called double stars. But sometimes the two stars in a double star really are at the same distance from us, and are caught in each other's gravity and orbiting around each other. We call these binary stars. But how can we tell if a double star pair is really binary? There are three ways. *visual binaries*, meaning we can see them both, and they are close enough to each other that we can watch them orbit each other. If they are sufficiently close to each other, they may orbit in hours. Or days. Or years. Or decades. Or centuries. That's one reason old astronomical photographs are so valuable; if a binary pair takes a few hundred years to orbit each other, it's only by comparing recent pictures with very old ones that we can notice their motion. I'm sure there are many binary stars that take thousands of years to orbit, and we don't yet know they are binaries. But what if the pair is so far away that it just looks like a single dot? Or what if one member of the pair is too faint to be seen? I'll just see one dot, but the spectrum will show two sets of spectral lines. As they orbit each other, unless their orbital plane is face-on to us, I'll notice their Doppler shifts as each one alternately comes towards us or recedes. Such a pair are called *spectroscopic binaries*; I see only a single dot, but the spectrum reveals a binary pair. The rarest cases are the *eclipsing binaries*, pairs whose orbital plane lies along our line of sight, so that each one eclipses the other in turn. By making a graph of how their brightness varies with time, called a light curve, I can see the dimming due to each eclipse. The length of each eclipse can even give me information about their diameters. So, if, by any of these three methods, I determine that a binary pair exists, I can use Newton's Law of Gravitation to work out their masses. What about solitary stars? I can't measure their masses directly, but there's an indirect method I can use. If I make a plot of the mass vs. luminosity for lots of binary stars, I can assume the same relationship applies to solitary stars, and use that plot to read off the mass of a solitary star whose luminosity I know. Of course, to calculate that luminosity in the first place, I'll have to know that star's distance! (Size) Recall from the chapter on telescopes that all the stars except our sun are so far away that no matter how much I magnify them, they still just look like dots. So how can I tell how large they are? (Again, don't confuse size with mass.) How can I get their diameters? Remember interferometry from the discussion of radio telescopes? A small handful of very large, very nearby stars are sufficiently large that optical interferometry with specially-built pairs of visible-light telescopes can resolve their disks, so we can measure their sizes directly â€" the direct method. For most stars, we have to use the indirect method. Recall the Stefan-Boltzmann law, that the amount of light a glowing object emits per unit area is proportional to a constant times temperature to the fourth power. We've already learnt several methods to measure the temperature of a star. (What are they?) So, if I know the temperature, I know the amount of light per area. Now, if I compare that to the total amount of light, I can calculate the amount of area the star has, and that's related to the diameter through the formula for the area of a sphere, 4*P*r2. Combining these two gives you the formula in your book. Astronomers divide stars into three size categories: Size Category Size (compared to Sun) Dwarfs <10 Giants 10<R<100 Supergiants >100 *****So, what size is our sun? That's right, our sun is a dwarf-sized star. Don't confuse these sizes with the groups on the H-R diagram. For the most part, stars in the supergiant group are supergiants in size, stars in the giant group are giants in size, and stars in the white dwarf group are dwarfs in size. Stars along the main sequence range from dwarf size in the bottom two-thirds up to supergiant sized at the very top. For this class, if I'm talking about the size of a star, I'll specify that; otherwise, you can assume I mean the groups on the H-R diagram. --------------------------------------------- Star Properties - Lifespan As we'll see soon, stars are powered by nuclear fusion. The majority of a star's lifespan is spent as a MS star, and all main sequence stars are fusing hydrogen into helium. Thanks to Cecilia Payne-Gaposhkin, we know that pretty much all stars start out about ¾ hydrogen, so their lifespan is proportional to their mass. Specifically, the lifespan of a star is proportional to how much fuel it has divided by how fast it's burning the fuel. Lifetime = mass/luminosity --- ---- --- ---- Stellar lifetimes range from about 10 million years for the largest O-type stars to a calculated hundreds of trillions of years for the smallest M-types. Lifetime = 1/mass3 --- ---- --- ---- Stellar lifetimes range from about 10 million years for the largest O-type stars to a calculated hundreds of trillions of years for the smallest M-types. ------------------------------------------ Star Properties - Variable Stars When we say a star is a variable star, we mean that it varies in brightness. Usually that is because a star is approaching the end of a particular nuclear fuel, and is soon to shift to another. (Variable Star Types) There are quite a few different types of variable stars, many of which are classified by the shapes of their light curves. Recall from the discussion of eclipsing binary stars that a light curve is a graph of brightness over time. Some vary irregularly (like Betelgeuse). Some vary sinusoidally (their light curve is a sine wave). The ones we're interested in here are called delta Cepheid variables, whose light brightens quickly, then dims more slowly, with periods ranging from a day or so to a couple of months. The class is named after one particular example, the fourth brightest star in the constellation Cepheus. Recall Johann Bayer's system for naming stars; the fourth brightest star in any constellation is the delta star in that constellation. (Henrietta Leavitt) Henrietta Swan Leavitt was another of the famous computers at Harvard College Observatory. Like Annie Jump Cannon, she was deaf, in her case due to an illness she contracted on a European trip. One of her research projects was studying variable stars in the Small Magellanic Cloud, a satellite galaxy of our Milky Way. She identified 1,777 variable stars there, and in particular studied 25 delta Cepheid variables. By assuming that all the stars in the Small Magellanic Cloud are at roughly the same distance, she was the first to notice that there was a simple linear relationship between the period of a delta Cepheid and its average brightness; the longer the period, the brighter the star. She commented that if anyone could determine the distance to any one delta Cepheid, the period could then be used to determine the distance to any delta Cepheid. Within a year, Ejnar Hertzsprung had done so. We'll see in another chapter that Edwin Hubble will use delta Cepheids in what was then called the Andromeda spiral nebula to show that that "nebula" is really another galaxy like our own; that the Milky Way is but one of countless galaxies in the universe. --------------------------------------------- Star Properties - Star Clusters No star can form in isolation; all stars form in star clusters. Although there are a minority of stars today that are solitary, most stars are members of multiple-star systems, the larger of which are known as star clusters. Solitary stars have strayed from the clusters in which they formed. There are two major types of star clusters (and a few minor ones that won't concern us here); open clusters and globular clusters. Open clusters outnumber globular clusters by an order of magnitude; there are over 1,100 of them in our galaxy, compared to at least 152 globular clusters. (Types of Clusters) Stars form when clouds of interstellar gas and dust (nebulae) develop clumps within them due to turbulent flow. If a clump is sufficiently dense and massive, its gravity will compress the material in it, and if it is compressed sufficiently, a star will form. A nebula with only enough material to form a single clump would not have enough gravity to hold itself together, much less to form a star, but when a nebula has enough material to form ten thousand or so stars, that's when there's sufficient gravity for stars to form. The formation process is only about 10% efficient, so the smallest star clusters have a minimum of a thousand or so stars; these are the open clusters. (Open clusters) are forming continuously, so some are old (NGC 6791 â€" remember what NGC stands for?), some are quite young (NGC 2362), and others are incipient (the Orion Nebula). Once an open cluster forms, star loss is common. Many do not have sufficient gravity to hold onto all their stars, that's why they're called "open", because stars can escape. The astronomical jargon is that open clusters are only weakly gravitationally bound. Our sun formed in an open cluster whose remnants form the bowl of the Big Dipper â€" that's our home. Below is a photo of a typical open cluster, M25. (Remember what the "M" stands for?) The blue stars in the foreground are the hot O-and B-type stars in the cluster. The bright yellow ones are A- and F-types or foreground stars. K- and M-types are too faint to be seen in this photo. Most of the evenly-distributed faint stars are background stars. (Globular clusters) have quite a few more stars, which gives them sufficient gravity to pull them into globe shapes, hence the name. We don't know much about their formation, but they are all very old, as old as the galaxy. They may even predate the galaxy. Below is a photo of globular cluster M15. Open Clusters********************** *Hundreds to a few thousand stars *Found in galactic spiral arms *All ages *Numerous (a few thousand per galaxy) *Not always gravitationally bound Globular Clusters******************** *A hundred thousand to ten million stars *Found in the spherical galactic halo *All very old *Less numerous (a few hundred per galaxy) *Gravitationally bound (Ages of Clusters) So, how do we tell the age of a star cluster? That's easy; just turn it over and read the date stamped on the bottom â€" just kidding! Clusters form quickly in astronomical terms; a nebula might become a star cluster in just a hundred thousand years â€" a long time in human terms, but the blink of an eye compared to the 13.7-billion-year age of the universe, so we can safely call all the stars in a cluster the same age. Recall that all stars start out as main sequence stars, so the H-R diagram of a young cluster would only show stars on the main sequence. Also recall the discussion of stellar lifetimes; more massive stars (the hotter and brighter ones at the top of the main sequence trend in the H-R diagram) age faster, less massive ones age more slowly. So, the H-R diagram of a brand-new cluster will have only MS stars. As the cluster ages, successively more of the stars at the top of the MS leave. They become giants, then either become white dwarfs, or become supergiants and blow up. So, you can judge the age of a cluster by how much of the main sequence is left on an H-R diagram.

Chapter 15

Our milky was galaxy we call the Milky Way, widest and brightest in the summer evening sky. The name comes from the Greek phrase galaxias kuklos, "milky circle". Galileo found that the Milky Way band is: * composed of distant stars. *The stars are not evenly distributed in the sky *they are concentrated in a particular plane. Henrietta Leavitt: *found a relationship between the periods and average brightnesses of delta-Cepheid variables in the Small Magellanic Cloud (SMC), * she predicted that if anyone could measure the distances to some nearby delta-Cepheids, we would then be able to calculate the distance to the SMC. Ejnar Hertzsprung: *measured the distance to some nearby delta-Cepheids, allowing us to determine that the clump of stars called the Small Magellanic Cloud is much farther away than any other object whose distance had been measured to date. (Its distance is currently measured at 199,000 light years.) One of the biggest puzzles in early-20th-century astronomy was the nature of the spiral nebulae. *constellation Andromeda being the biggest and brightest. -Some people had proposed that they were clouds of gas spiraling inward to form individual stars -others thought they were vast groupings of stars that were so far away that individual stars in them could not be seen. Vesto Slipher: in 1912 found that they did not have the expected emission spectra from clouds of gas, but instead had absorption spectra like star clusters. *He also determined from their Doppler shifts that all of them except the one in Andromeda were going away from us. Heber Curtis: *1917 he observed a nova in the Andromeda Nebula, searched back through old photographs, and found 11 more. Noting that they were much fainter than other novae, *he concluded that the Andromeda Nebula was much farther way than the SMC. Still, nobody had seen ordinary stars in spiral nebulae; they were just too far away, which made their stars too faint. Swedish astronomer Knut Lundmark: 1922 he was the first to observe individual normal stars in the spiral nebula M33 in the constellation Triangulum -John Duncan used what was then the world's largest telescope, Caltech's Hooker 100-inch, to observe variable stars in M33. Two years later Edwin Hubble photographed the Andromeda nebula with the Hooker 100-inch and also resolved individual stars. *He identified and measured the light curves of some delta-Cepheids in this vast structure, and determined that it was indeed much farther away than the SMC. (Its distance is currently measured at 2.5 million light years.) So, there were vast reaches of empty space between the known stars, the SMC, and the Andromeda nebula *Hubble's observations suggested that the large clump of stars formerly known as the Andromeda Nebula contained more stars than the previous estimates for the total number of stars in the universe! -Astronomers at first referred to the spiral nebulae, and their elliptical cousins, as "island universes" -but Harlow Shapley coined the modern use of the term galaxy, taken obviously from the old name of the Milky Way, -which is now known to be just another of an estimated two trillion galaxies in the observable universe. --------------------------------------------- Stellar Reincarnation Recall from the Stellar Evolution: - after high-mass stars explode as supernovae, the material from their outer parts gets returned to the interstellar medium and gets recycled into the next generation of stars. This was indicated by the arrow looping up the right side of the flowchart. Since stars fuse lighter chemical elements into heavier elements, this means that each new generation of stars is further enriched in heavy elements; from none after the Big Bang, the universe has now reached a concentration of about 2% of elements more massive than H and He. The expanding bubble of hot gasses from a supernova will expand to about 100 light years across before it slows and merges with the ISM. But recall that stars must form in clusters, and that star formation is quite rapid compared to the lifespans of stars. when all the massive stars that formed together in a cluster all reach their ends and explode within a few hundred thousand years of each other, their expanding bubbles of hot gas merge into superbubbles thousands of light years across. When these superbubbles expand beyond the galactic disk into the halo where the ISM is much thinner, the gas in them shoots away from the disk in galactic fountains. *It lacks sufficient speed to escape from the galaxy, so eventually it cools, slows, and rains back down into the disk to start the star-forming process over again. spiral arms that show up in the disks of spiral galaxies? We now know that they are ripples (known technically as spiral density waves) caused by the gravity from other galaxies passing nearby. As nebulae revolve through these spiral arms, they are compressed, triggering star formation. Oddly, the direction of spiral of the spiral arms is NOT related to the direction of rotation of the galaxy; it's related to the direction in which the passing galaxy that caused them was moving. --------------------------------------------- The Centre of the Milky Way the centres of most, if not all, galaxies contain supermassive black holes. -the black hole cannot be seen -the recent photo that made news on the Internet was actually an image of the accretion disk around it. -We detect it by the radio emission from a cloud of gas orbiting it, a radio source named Sagittarius A*. -By analysing the orbits of stars near it, we've used their motion to calculate the mass of the object they're orbiting -the black hole turns out to have a mass about 4 million solar masses.

Chapter 19 Milky Way galaxy is a spiral galaxy. Technically it's a barred spiral It consists of a flat disk called the disk, a central bulge called the central bulge, and a spherical halo called the halo. -Within the disk are spiral arms called ? Spiral arms The painting below by Pablo Carlos Budassi is one of the most accurate depictions of our current understanding of our own Milky Way galaxy. ---------------------------- The disk: *filled with stars of all ages, and clouds of gas and dust, which are the ejecta from old stars, and which will eventually form into new stars. The stars in the disk revolve around the central bulge, mostly in the same direction because that's the direction the gas cloud the galaxy formed from was revolving. There are a few streams of stars going the wrong way, the remains of smaller galaxies that have been cannibalized by our own. Our own Sun is in the disk, about two thirds of the way out toward the edge. Then there's the central bulge. The stars there are mostly old, and many don't orbit in any particular direction, nor in a particular plane. A few do, in elongated orbits in the plane of the disk. the halo: which mostly consists of globular clusters. Like most of the stars in the central bulge, these clusters don't orbit in a particular direction, nor in a particular plane. What this is telling us is that the stars in the bulge and halo formed before centrifugal force flattened the galaxy down into a disk. Our Milky Way galaxy is part of a small local group of several dozen galaxies that we call "the Local Group" *ours is the second largest galaxy in the Local Group, after the Andromeda Galaxy that is about 50% larger than ours. Kepler's Second Law: planets move faster when closer to the Sun. This law should apply to any small objects orbiting a larger object, yet when we apply it to stars orbiting the centre of the Milky Way, it doesn't work. Stars out at the edge of the Milky Way are orbiting about as fast as stars near the centre! And that not just true for our galaxy; it seems to be true for the other spiral galaxies as well. There's only one reasonable explanation. Although the stars in the galaxy are more concentrated toward the centre, and the interstellar medium (ISM) is in the galactic disk, most of the mass of the galaxy is out in the halo. Since that mass is invisible all across the electromagnetic spectrum, it's called dark matter. The majority of the mass of our galaxy (and the universe) is dark matter. The sort of matter we're used to, composed of protons, neutrons and electrons, makes up only 20% of the matter in the universe. ------------------------------ History of the Milky Way a major purpose of classification is to help us understand complex topics. the Milky Way, with over 200 billion stars, qualifies as a complex topic! We've talked about a couple of classification schemes for stars: *the spectral type classification and the H-R diagram. Here's another useful one, the division into Population II and Population I stars. Population II stars are older. -Their orbits are inclined to the disk, and they are found in the central bulge and the halo. -They have very low levels of heavy elements, suggesting their great age. Population I stars are younger. -They orbit mostly in the disk, with a few in the central bulge. -They have higher levels of heavy elements, suggesting they formed later in the history of the universe. [And yes, there was quite likely a first generation of stars, now called Population III. -They had no heavy elements at all, -related to the role of heavy elements in trapping radiation, they were much more massive than today's stars, and extremely short-lived. The Big Bang: -was loud. -When sound disturbs the motions of particles, they tend to drift away from the crests and troughs of the waves, and congregate in the slack areas. -The gas atoms in the early universe surfed this way on the sound waves from the Big Bang, congregating into clumps that would become the galaxies. These early protogalaxies at first were shrinking spherical-ish blobs of gas, and it was in them that the Population III and Population II stars formed. the formation of our Solar system that conservation of angular momentum decrees that a rotating flexible object will flatten into a disk -that's how all our planets ended up in one plane. -That's also how the gas in our collapsing protogalaxy collapsed into the galactic disk, where the Population I stars form and reform today.

1. The name of our galaxy: Milky Way 2. the milky way's spiral arms are located: in the disk 3. Our milky way galaxy is part of a small group of galaxies called: Local Group 4. We've called the diffuse band of light in the sky the milky way since ancient greek times, but when did we realise...: in the early 20th century 5. which stars are older? population II 6. which direction is this galaxy rotating? its impossible to tell from the picture (look like they point clockwise) 7. most of the mass in the milky way is in the form of: dark matter 8. What broke up the gas in the early universe into the clumps that would become galaxies? sound 9. how do we know that there is a supermassive black hole in the centre if our milky way galaxy? By the radio emissions from gas orbiting it 10. most of the milky ways globular clusers are located: in the halo 11. Our sun is in the milky ways: disk 12. streams of star that revolve backwards in the milky way are evidence: that the milky way has swallowed small galaxies 13. most of the mass in the milky way is located: in the halo 14. Which part of the milky way galaxy has lots of gas and dust, and the new star formation? the disk 15. Our milky way is an: spiral galaxy

Chapter 19 quiz

If you lay a thermometer in the sunlight, its temperature rises, so when people were experimenting with prisms and splitting sunlight into its constituent wavelengths (colors), it was natural to wonder whether the heat was carried evenly by all colors, or concentrated in one particular color. Surprisingly, the temperature rose most when the thermometer was placed not in any color of light, but just outside the red region of the spectrum. There must be an invisible color which is perceived as heat. Today we call it infrared. Later another invisible color was discovered out beyond the violet, and named ultraviolet. Today we know that visible light constitutes only a tiny fraction of the entire electromagnetic spectrum, and we understand how the properties of wavelength, frequency, and energy varies from one type of electromagnetic radiation to another. Astronomers are interested in studying the sky at all wavelengths. Many astronomical objects only emit certain types of electromagnetic radiation, so without a telescope operating at the right wavelength, we never even know of those objects. Others look very different at different wavelengths, so that each new type of telescope teaches us undreamed-of facts about familiar objects. One major problem is that the Earth's atmosphere is opaque to much of the electromagnetic spectrum. The atmosphere is transparent to visible light (obviously, since we can see out) and a very, very tiny portion of ultraviolet (enough UV to cause sunburns, but not enough to be astronomically useful). Our atmosphere is transparent to high frequency radio waves, but not to wavelengths longer than about 10 meters. Some infrared light penetrates part way to the ground, and can be detected from mountain tops or high-flying aircraft, but not from sea level. This means we can put visible light telescopes and radio telescopes here on Earth, and infrared telescopes on mountain tops, but telescopes for microwaves, most infrared, ultraviolet, X-rays, or gamma rays must be placed above the Earth's atmosphere, in orbit.

Chapter 5 (Electromagnetic spectrum)

As the textbook states, all macroscopic objects constantly emit electromagnetic radiation. You do. Your chair does. An ice cube does. The Sun does. We can take the radiation coming from any object and split it apart into its constituent wavelengths using a variety of technologies, such as a prism. If we do that, many glowing objects are seen to emit a very broad band of wavelengths, stretching from the low energy end of the EM spectrum (radio), up to some characteristic cutoff wavelength. Light sources which do this are said to display a continuous spectrum - within the broad band, each wavelength is present and blends smoothly and continuously into the next. (There are two other types of spectra which will be discussed later.) Experiments showed that many objects, when heated to incandescence, produced continuous spectra, but that if the object had a distinct color of its own, the spectrum would be a bit distorted from this ideal. Work therefore focused on studying the light from incandescent objects which had no intrinsic color when cool, i.e., were black. Such objects produced the simplest spectra, and are known as blackbodies. Study of blackbodies led to a theoretical understanding of how incandescent objects glow, and what the light from them will be like. For the remainder of this chapter, we shall focus on the behavior of light from sources which produce blackbody continuous spectra. The word spectrum (pl. spectra), by the way, is the Greek word for rainbow. An instrument designed to split light into its constituent wavelengths is called a spectroscope. If the instrument is capable of producing a record of the spectrum (photographic, graphical, or digital), it is a spectrograph. Before the blackbody curve was ever plotted, physicists had already written mathematical descriptions of two aspects of the behavior of light from incandescent objects. You've probably noticed that when an object is just barely hot enough to glow (like an electric stove burner on 'low'), it glows red. A hotter object (like molten steel or the surface of the Sun) may glow yellow, while a really hot object (like a spark or a drop of metal from a welding torch) glows blue-white. Remember that within the visible spectrum, red is a long wavelength, blue is a short wavelength. Wien's Law is an equation which relates the temperature of a glowing object to the wavelength of light it will emit the most of, known as lambda max. We can use the Wien's Law equation in one of two ways. -We can calculate the color of light from an object at a particular temperature, -or we can measure the light and use the equation to calculate the temperature. This is how we know the temperature of the Sun is 5,800K, or how firefighters can assess the character of an industrial fire. The Stefan-Boltzmann Law was previously known as Stefan's Law until it was learned that Boltzmann derived it before Stefan. It is a mathematical description of the well-known fact that hotter objects glow more brightly than cooler objects. Let us summarize: ---------Temperature Dependence of Radiation Emission-------------- *Everything emits electromagnetic radiation. *The Stefan-Boltzmann Law - As an object's temperature increases, the amount of radiation also increases. *Wien's Law - As an object's temperature increases, the frequency of the radiation increases, and the wavelength decreases. *Cole's Law - Thinly sliced cabbage with mayo and vinegar. Initially, the physical reasoning about the atomic processes behind these laws seemed contradictory. It seemed that if the Stefan-Boltzmann Law were true, Wien's law could not be, and vice versa. A physicist named Max Planck was able to solve the discrepancy and produce one equation which combined both laws. His solution, and his equation, are too complex for us here, but his equation could be used to predict the shape of a spectrum from an incandescent object, and what it predicted looked just like the blackbody curve! Examine the blackbody curves in the textbook for objects at four different temperatures. Notice how they illustrate both the Stefan-Boltzmann Law and Wien's Law. As the temperature increases, the brightness increases (the curve moves up), and the frequency increases (the curve shifts to the right.) I had a wonderful 7th-grade Physical Science teacher who used lots of demonstrations. We made mashed potato glaciers on inclined boards and put horizontal rows of toothpicks across them to demonstrate that the centers flow faster than the edges. She had a favorite demonstration to illustrate the Doppler effect; she would run down the hall past the classroom, screaming at the top of her lungs. (I think she did it to annoy the math teacher next door.) As she went past the door, we would hear a drop in pitch, even though she stayed on the same pitch all the way down the hall. It was a memorable demonstration of the Doppler effect on sound, the sound waves being shorter (higher pitch) as she came toward us, and longer (lower pitch) as she receded. You can hear the same thing from any passing car. The Doppler effect works on any waves, including light. Of course, wavelength is not perceived as pitch, but as color. A light source moving toward us will be seen as bluer than normal (shorter wavelengths), while one moving away from us will be perceived as redder than normal (longer wavelengths). The effect is speed-dependent; the faster an object is moving, the greater the shift. We can use this effect to determine the speed and direction of motion of a star by observing its spectrum.

Chapter 5 (Information from light)

When an electromagnetic wave passes, what is it that's waving? Nothing: the strength of an EM field fluctuates. If the wavelength of light increase, the frequency: decreases Which has more energy, radio waves or gamma rays? Gamma rays Which has the longer wavelength? Microwaves Which is true? Hotter objects glow brighter than cooler objects Which is true? hotter objects glow brighter than cooler objects A glowing objects coming towards us will have its light shifted to: shorter wavelengths A spectrum with MOST colors missing, but a few present, is called an: emission spectrum The spectra of most stars are: absorption spectra A hot, high pressure gas will produce what type of spectrum? continuous spectrum Orbital electrons tend to move? towards the nucleus Which particle is found outside the nucleus? an electron Which particle carries a negative electric charge? an electron An absorption spectum involves: away from the nucleus The planets in our solar system have: absorption spectra

Chapter 5 quiz

For most of the history of humanity, our knowledge of the Universe came from our five senses. For objects in the sky, this knowledge was acquired solely through the sense of sight. While optimized for use at ground level, the eye is not a particularly powerful tool for studying the rest of the Universe. The telescope became the tool for collecting and concentrating light to enable observers to see greater detail and fainter objects than was possible with the eye alone. The telescope was invented around 1607 in Denmark or Holland. Called an Optik Tube, it quickly became popular throughout Europe as a novelty. A friend of Galileo's saw one in Paris in 1608 and sent a description to him. Galileo quickly recognized that it could be used to study the sky as well as terrestrial objects. After constructing an Optik Tube of his own, Galileo became the first person to look at celestial objects through the telescope and describe what he saw. Those observations and their consequences were described back in Chapter 3. Originally, telescopes were used to observe only in the same region of the electromagnetic spectrum to which the eye is sensitive. Today, such telescopes are referred to as optical telescopes. In today's parlance, a telescope is any device that collects and concentrates electromagnetic energy. As a result, in addition to optical telescopes, we also have radio telescopes, ultraviolet telescopes, infrared telescopes, X-ray telescopes and gamma ray telescopes. Most of this chapter is devoted to the optical telescope since that is the oldest type and still the most common. Many of the principles behind the operation of optical telescopes do apply, however, to telescopes operating in other parts of the electromagnetic spectrum. There are two primary categories of optical telescopes. Those that use a large lens as the primary light gathering device (refracting telescopes) and those that gather and concentrate the light by means of a mirror (reflecting telescopes). Galileo's several telescopes were all of the refracting variety. About 50 years later, Sir Isaac Newton devised a practical telescope using a mirror instead of a lens. This basic style of reflecting telescope is still called a Newtonian telescope. Refracting telescopes have certain disadvantages, especially in larger sizes. Most of the problems come from the fact that the light passes through the lens. When light travels from one medium to another each wavelength (color) follows a slightly different path. In a simple lens, the violet light reaches focus closer to the lens than red light. This is called chromatic aberration. Early attempts to correct this involved minimizing how much the light was bent. This led to very long focal lengths compared to the diameter of the lens. Maneuvering a telescope 6 inches in diameter with a one hundred foot focal length (a focal ratio of f/200) was not easy. More manageable refracting telescopes were created by producing compound lenses. By combining two lenses, one thicker in the middle and the other thinner in the middle, it is possible to create a "lens" where any two wavelengths are brought to exactly the same focus. If the effective focal length is no shorter than 15 times the diameter (focal ratio of f/15), then most other colors come close to the same point. By having three elements in the compound lens, any three colors can come to the same focal point. Early camera lens were of this "triplet" design. Since early films were only sensitive in the blue and violet, adequate lenses could be made if the focal length were no shorter than about 5 times the diameter (f/5). With the advent of films sensitive over most of the visible spectrum, more complex lenses were required. Early "color corrected" lenses had five elements. Modern computer designed lenses have four to eight elements. Zoom lenses can have up to 15 elements, several of which move to change the effective focal length of the lens. Because of the complexity of lenses that adequately correct for chromatic aberration, large lenses become very expensive. For astronomical use, lenses normally will have only two elements in combination with a moderately long focal ratio (f/12 to f/18). The largest astronomical lens, at the University of Chicago's Yerkes Observatory at Green Bay, Wisconsin, has a diameter of 1 meter (40 inches). Attempts to build larger lenses are hampered by several factors. The larger the lens, the thicker it has to be in order not to sag under its own weight. This is complicated by the fact that a lens can only be supported around its edge. Since the light must pass through the glass of the lens, some light is absorbed. The thicker the lens, the more light is absorbed. Since the light must pass through the glass of the lens, the lens must be optically pure and without stress or bubbles. The larger the lens, the more difficult this becomes. Reflecting telescopes solve most of the problems inherent in refracting telescopes. Since the light does not go through the mirror, the mirror can be made of any substance that reflects light and can be shaped to a very precise curve. There is no chromatic aberration. Large mirrors can be supported across their backs and can be made much larger than lenses. The mirrors in early reflecting telescopes were made of a metal alloy that would take a very high polish. The main disadvantage of this alloy was that when the metal eventually corroded, re-polishing could also change the shape of the mirror. This was solved early in the 19th century when a technique was developed to make the mirrors out of glass. Glass mirrors are polished on their front surfaces to the exact curvature needed for each mirror. A coating of silver is then chemically deposited onto the mirror surface to form the reflective layer. After a few years, when the silver eventually begins to corrode, it can be chemically removed and redeposited without affecting the shape or smoothness of the glass surface. In modern reflecting telescopes, the silver surface is replaced with vapor deposited aluminum which is more reflective and more durable. ------------------------------------------- We can describe three different "powers" of a telescope. Each refers to a particular capability of a telescope. The powers can refer equally to a reflecting or refracting telescope. The powers described below are magnifying power (magnification), light gathering power, and resolving power (resolution). ----------Magnifying Power--------- Magnifying power describes how much larger the object being viewed appears when you are looking through the telescope compared to what you would see without the telescope. It is the least important of the "powers" since it can be changed easily by changing the eyepiece. The telescope consists of two primary optical elements. The main lens or mirror which first encounters the light from the object being viewed is called the object lens, or object mirror, or more simply the "objective". At the other end of the telescope where the light from the objective emerges, a smaller lens is used to magnify the image produced by the objective. This small lens is called the eye lens or eyepiece. The image produced by the objective will have a size that is determined by the focal length of that lens or mirror. The longer the focal length of the objective, the larger an image it produces. This is independent of the diameter of the objective. Since the eyepiece is used as a simple magnifying glass, its behavior is the same as any magnifying glass. This is to say, the shorter the focal length of the eyepiece, the more it magnifies the image formed by the objective. The magnifying power of a telescope can then be found by simply dividing the focal length of the objective by the focal length of the eyepiece. M = F / f Where M is the effective magnification of the telescope, F is the focal length of the objective and f is the focal length of the eyepiece. For a given telescope, using a shorter focal length eyepiece will give you a higher magnifying power and using a longer focal length eyepiece will give you a lower magnifying power. For a given eyepiece that might be used on several different telescopes, you will have a larger magnification with a telescope that has a longer focal length objective than on one that has a shorter focal length objective. There are limits to both the maximum and minimum magnifying power. There are also situations where lower magnifying powers would be preferable. As you lower the magnifying power by substituting an eyepiece with a longer focal length, your apparent field of view (the part of the sky you can see) increases and the image gets brighter. When the column of light leaving the eyepiece is the diameter of your dark adapted pupil then you have the brightest possible image showing you the widest possible view of the sky. This is what is called a richest field. This is the best situation for viewing nebulae, star clusters, galaxies and comets. All of these are faint, diffuse objects and are best viewed at lower powers. Assuming that the fully dark adapted human eye has a diameter of about 1/4 inch, then the minimum useful magnifying power is about: M min = 4 x D inches As you increase the magnification, you are taking the fixed amount of light coming into the telescope and spreading it over an increasingly larger area. Your view through the eyepiece will show you a smaller and smaller portion of the sky. Eventually, you will increase the size of the image to the point that you can see all of the information that is contained in the image (see resolving power below). At that point, if you increase the magnification, the image will just get, bigger, fuzzier, and fainter. The maximum usable magnification for a telescope is about: M max = 50 x D inches The maximum usable magnification on all but the smallest of telescopes is limited by the steadiness of the earth's atmosphere that you must look through. It takes a night with very steady air (called good "seeing") to use the maximum power. For larger telescopes, regardless of the theoretical maximum power, it is extremely rare that magnifications over 1000X can ever be used. When buying a telescope, be very careful of the advertised magnifying power. It is not unusual to see advertisements for telescopes with powers of 600X. Typically, the diameter of the objective will be 60 mm (2.4 inches). The theoretical maximum power for such a telescope is 50 x 2.4 = 120. While there are eyepieces supplied to achieve the advertised 600X, anything over 120X will be worthless. For the typical amateur astronomer, powers of 15X to 40X will be used for viewing faint diffuse objects like comets and nebulae, power of 50X to 150X will be used for the moon and planets and, when "seeing" is exceptional, higher powers (to the theoretical maximum) can be used for these brighter objects. -----Light Gathering Power----- One of the major purposes of a telescope is to gather and concentrate light, making faint objects appear brighter. The amount of light that a telescope can gather is equal to the surface area of the objective (main lens or mirror). The area of a circle is equal to: Area = 1/4 x pi x Diameter2 A larger telescope (1) gathers more light than a smaller telescope (2) in proportion to the areas of their objectives (LGP = Light Gathering Power): LGPrelative = Area1 / Area2 Substituting for the areas using the first formula in terms of the diameters we get: LGPrelative = 1/4 x pi x Diameter12 / 1/4 x pi x Diameter22 After canceling similar terms in the numerator and denominator we get: LGPrelative = Diameter12 / Diameter22 If we were to now compare an 8 inch diameter telescope's light gathering power with a 2 inch telescope we find: LGPrelative = 82 / 22 = 64 / 4 = 16 This tells us that the light gathering power of an 8" telescope is 16 times greater than that of a 2" telescope. The 8" telescope would let you see objects 16 times fainter than what you could see with the 2" telescope. It is common to express the LGP for a telescope in terms of the human eye. Assuming the diameter of the dark adapted human eye to be 1/5 inches (this is traditionally a more conservative estimate than used above for the minimum usable magnifying power), if we let Diameter2 represent the eye, then our formula becomes: LGP = Diametertelescope2 / Diametereye2 After substituting values and simplifying the notation to make Dinches the diameter of the telescope in inches we have: LGP = Dinches2 / (1/5)2 Which becomes: LGP = Dinches2 / (1/25) Or: LGP = 25 x Dinches2 A common size of binoculars (just one telescope for each eye) is described as 7x50. This means 7X magnification and an objective diameter of 50 mm. Since 50 mm is about 2 inches, this is a richest field telescope (7X is about 8X, what the Mmin would suggest). The LGP would then be: LGP = 25 x Dinches2 = 25 x 22 = 25 x 4 = 100 When used at night, with your pupil fully dilated, objects viewed through 7x50 binoculars will appear 100 times brighter. This is why 7x50 binoculars are sometimes called "night glasses". During the daytime, objects do not appear 100 times brighter because the pupil of your eye is constricted and most of the light does not enter the eye. A common telescope used by amateur astronomers has a diameter of 8". The LGP of such a telescope would be: LGP = 25 x Dinches2 = 25 x 82 = 25 x 64 = 1600 The 400" Gran Telescopio Canarias on the Canary Islands has a LGP of: LGP = 25 x Dinches2 = 25 x 4002 = 25 x 160,000 = 4,000,000 This is one of the main reasons that large telescopes are still being built at the surface of the earth in this time of space-based astronomy. Large telescopes are "light buckets". -----Resolving Power-------- Because of the wave nature of light, there is a limit to the amount of detail that a telescope can provide. Your text provides the general formula that expresses the resolving power of a telescope. The resolving power is expressed as the minimum angular separation that two point sources of electromagnetic energy (light) can have and still be seen as two distinct objects. Because of the diffraction that occurs with electromagnetic waves as they pass through a telescope, a point source of light appears as a small spot. The smaller the aperture of the telescope, the larger the spot. The general formula for Resolving Power, in metric units, is: Resolving Powerarc seconds = 1/4 x Wavelengthmicrons / Diametermeters Telescopes operating at short wavelengths (X-Ray, UV and visible light) do not have to be very large to provide fine detail. Radio telescopes, that can be operating at wavelengths of millions of microns, need to be huge. Before the general theory of diffraction was developed, the English astronomer Charles Dawes viewed a great number of double stars (stars very close to each other in direction) under excellent seeing conditions in a variety of telescopes and developed a preliminary version of the above formula that is called Dawes' Limit. Since Dawes was working entirely in the visible part of the spectrum, the wavelength factor was incorporated into the constant that Dawes determined empirically. Since Dawes was English, the units are, of course, also English. The relationship he found was: Dawes' Limit arc seconds = 4.5 / Diameter-inches According to Dawes' Limit, a 4" telescope can show double stars that are at least 1 arc second apart. A 8" telescope can reveal as separate two stars that are at least 0.5 arc seconds apart. In theory, the 200" telescope at Palomar should be able to resolve two stars that are 0.02 arc seconds apart. In practice, "seeing" is never steady enough to allow anything less than 0.25 arc seconds. The Hubble Space Telescope (about 100" in diameter) can, and does, reach Dawes' Limit at 0.04 arc seconds (for it) because it is outside the atmosphere. Resolving Power is always expressed in terms of the separation of two point sources under very high contrast conditions. When viewing the moon or planets, the contrast is much less and features generally need to be larger than Dawes' Limit to be detectable. For comparison, a feature on the moon that is 1 mile in diameter is also about 1 arc second in angular extent.

Chapter 6 Telescope

Which form of reasoning is flawless provided the input statements are correct?

Deductive reasoning

Hipparchus of Rhodes (146 BC to 127 BC):

Developed the first star charts that also included a systematic method of comparing the relative brightnesses of the stars. By comparing earlier star charts to his own, he was the first to describe the precession of the earth's axis. He also proposed a simplification of Aristotle's model for the solar system by introducing the concept of equants that improved the accuracy of the system.

Eventually, some ideas survive so many tests that we run low on new ways to try to disprove them. When ideas have reached the point where they are very widely accepted in the scientific community, and when nobody can think of new tests to do (or when the only new tests imaginable are beyond our capability), then those ideas are granted a new name, theories. Very few ideas in science have the status of a theory. Older sciences like physics tend to have more, while younger ones like biology often have fewer. Some new ideas may reach theory status in decades, others have not gotten there in centuries. You're probably familiar with a few scientific theories, like those on gravity, evolution, or plate tectonics. Is a theory proven? By no means! Remember, nothing is ever considered proven in science. But a theory is widely accepted because it has survived hundreds or thousands of attempts to disprove it. This does not mean that new evidence could not disprove a particular theory tomorrow, but it is more likely that new evidence will simply lead to the modification of the theory. Studies of motion at very high speeds and near large masses led to the modification of Newton's Theory of Universal Gravitation. The modifications added by Lorentz and Einstein are called relativity. Improved studies of the fossil record and studies of evolution in action over many generations of short-lived organisms such as annual plants, fruit flies and bacteria have led to modifications in Darwin's original Theory of Evolution, but the theory still stands.

Don't be misled. The scientific method has been extraordinarily successful at helping us understand the natural world around us. It can tell us why all the planets go around the Sun in the same direction (and we'll learn that in a later chapter.) It can tell us why it rained today (but only give us a percent likelihood that it will rain tomorrow.) It can tell us why the gold is in California, not Oklahoma. In other areas it doesn't do so well. Psychology can offer a few insights on why my fantasies differ from my lover's, but can't offer a really profound explanation, or predict those of my offspring. In general, the inanimate world has been easier for us to understand than the world of living things. Physics progressed more rapidly than biology, although there are still major unanswered questions in both fields. The mind and thought have proven yet more difficult, either individually (psychology) or collectively (sociology, history). There have been some spectacular failures in which scientific ideas have been applied to areas in which we just don't know enough. (Government for example, witness communism.) There is room for many systems of thought in everyday life, and each is better suited for some areas than others. The scientific method works poorly in law for example, while the system of legal evidence works equally poorly for predicting the weather. The existence of a supreme being remains an area for philosophy, theology, and faith; science has had little success in this area. Some people see a fundamental conflict between different systems (especially science and faith), others, like myself, see no conflict at all.

Don't confuse the terms nearside and farside, which refer to the faces we can and cannot see, with the term darkside, which simply means whichever side is in darkness at the time

During a full moon, the farside is the darkside. During a new moon, the nearside is the darkside.

Johannes Kepler decided that planet orbits are what shape?

Elliptical

********Forms of Energy********* A technical definition of energy (the ability to do work, but then we'd have to define "work") is beyond the scope of this class, but it will be very helpful to be familiar with several different kinds of energy, and to be able to see how planets operate by converting energy from one form to another, or how stars operate by converting matter into energy. (Energy can also be converted into matter) Kinetic energy: energy of motion. The preposition is important here. This is not energy that is the result of motion, nor energy that causes motion. It is the energy of motion; the energy something has because it is moving. Radiative energy: energy of light. This isn't quite right; light is one of many different forms of radiative energy. Radiative energy is just energy radiating outward, so sound is a form or radiative energy. The kinetic energy of students radiating outward from a classroom after class is a form or radiative energy. But for this class, light is definitely the most important form of radiative energy, so we can live with the simplification. Potential energy: stored energy. Energy can be stored in many different ways. A plant can harness sunlight, using the photosynthetic enzyme Rubisco to manipulate molecules of water it takes in through its roots, and carbon dioxide it takes in through its leaves, and creating new chemical bonds that store the sunlight as chemical energy in sugars, or in the sugar polymers called starches. I can then eat that plant, digest those starches and sugars, and turn that energy into the bond energy of phosphate groups on a molecule called ATP, that will carry that energy to where its needed in my cells. Or if two chemicals tendto react with each other, I can keep them separate, but let electrons flow from one to the other; I have a battery turning chemical energy into electrical energy. Or I can take large molecules produced by living things, and release their chemical bond energy by a chain reaction that breaks the large molecules into smaller ones. The energy of this combustion is released as light and heat. Or maybe I can store the energy mechanically when I wind up a watch spring. (Which is really just chemical storage by bending lots of chemical bonds.) Then I can release it to power the watch. The Big Bang was the biggest release of energy ever, and some of that energy was kinetic energy that caused lots of particles to move apart. Today stars are releasing that stored energy by allowing those particles to fuse together again. Gravitational potential energy: energy stored due to an object's position away from the center of a gravity field. Gravity attracts things to other things. If I'm holding a brick, it's not where gravity wants it to be, which is at the center of the Earth. So the brick has gravitational potential energy, due to its not being at the Earth's center. If I let it go, that gravitational potential energy will start to be converted into kinetic energy as the brick falls. Thermal energy: energy of heat. Today we know that when something is hot, what that really means is that the atoms and molecules that make it up are vibrating or rotating quickly, so another way we can think of thermal energy is as the total kinetic energy of the atoms and molecules in a material. Mass-energy: energy available by conversion of matter into energy. Only nuclear or subatomic particle reactions can do this. The amount of energy released upon conversion of matter into energy is tremendous. It's calculated with Einstein's famous equation from Special Relativity, E=mc2. Since the speed of light, c, is quite large, and squaring it results in an even larger number, tiny amounts of matter convert to huge amounts of energy. For example, if I convert the single gram of matter in a typical paper clip into energy, the energy released would be the same as I'd get from detonating 21,500 tons of TNT (21.5 kT). For comparison, the atomic bombs used in WWII had yields of 15 kT(Hiroshima) and 20 kT (Nagasaki). Stars fuse hydrogen into helium, and have a little bit of mass left over. Some of that mass gets converted into energy, and that powers the stars. *******Heat vs Temperature******** Rotate/revolve, mass/weight; another such pair is heat and temperature. They are not the same, and the distinction is critical for us. -Heat is the amount of thermal energy a material has, -temperature is the concentration of thermal energy. Suppose I have a standard candle. Standard candles were once widely available from scientific supply houses for different purposes. They were made from particular waxes, in particular sizes, with particular sized wicks made of particular materials. One sort of standard candle might produce a certain amount of light, another might deliver heat at a certain rate. Suppose I have a standard candle for heat, delivering a certain amount of heat per minute. Let's say that I hold a tablespoon of water over that candle for one minute; the temperature of that water will go up by a certain amount. But now let's say I hold a bathtub of water over that same candle for the same length of time. I've delivered the same amount of heat to the bathtub as I did to the candle, but has the temperature gone up as much? Of course not. The thermal energy is now spread throughout the much bigger volume of water in the bathtub. The concentration of thermal energy (the temperature) is lower. In terms of the particles of which a material is composed, thermal energy is the total kinetic energy of those particles, while temperature is the average kinetic energy of those particles. *********Temperature Scale********** There are four major temperature scales. -The Fahrenheit, Celsius and Rankine scales were named after people with those last names, while the Kelvin scale is named after William Thomson*, the first British scientist in the House of Lords. We often compare temperature scales by citing the absolute zero, the freezing point and the boiling point of water in each. The scale of Daniel Fahrenheit (inventor of the mercury-in-glass thermometer) dates to 1724, and has the boiling point of water at 212 degrees F, the freezing point at 32 degrees F, and absolute zero at -460 degrees F. (The zero point in the Fahrenheit scale was at the coldest temperature Fahrenheit knew how to reach, using a three-part mixture of ice, water, and ammonium chloride salt. The scale of Swedish astronomer Anders Celsius (the man who discovered the connection between the aurorae and changes in the Earth's magnetic field) has the boiling point at 100 degrees C, the freezing point at 0 degrees C, and absolute zero at -273 degrees C. Celsius' scale was named the centigrade (100-step) scale until 1948, when it was renamed in his honour. Both of these scale present scientist with a problem. Many physical phenomena vary with temperature, and in the equations that describes that variance, temperature is often in the denominator of a fraction. If the temperature is zero degrees, that results in attempting to divide by zero, an undefined operation in mathematics. This was solved by simply taking each of the existing scales and lowering them so that their zero points were at the lowest possible temperature, absolute zero. Thus in 1848 Glasgow University engineer and physicist William Thomson, 1st Baron of Kelvin, created the Kelvin scale, while in 1858 Glasgow University engineer and physicist William Rankine created the Rankine scale. So which one will we use? The textbook uses Kelvin. I shall use Kelvin for stars, but in order to make the temperatures on various planets more relatable, I shall use Fahrenheit for planets. *Seriously. He was elevated to 1st Baron Kelvin, taking the name from the Kelvin River which flows past the University of Glasgow. The word "Kelvin" comes from Gaelic "caol abhuinn", "narrow river".

Energy and Temperature

Pope

Pope consulted the astronomer Clavius who pointed out the 11-minutes-per-year problem. He suggested a change in the leap year rule to fix it. The new leap year rule was defined as: every year evenly divisible (using Dionysius Exiguus' dating) by four would be a leap year unless it was a century year (ending in "00"). Century years are not leap years unless they are evenly divisible by 400. Those century years divisible by 400 are leap years

The New General Catalogue of Nebulae and Clusters of Stars:

Objects in it begin with NGC followed by numbers, but the objects aren't stars. Instead, the NGC lists non-stellar objects from outside our Solar system, objects such as nebulae and star clusters. The NGC predates the 20th-century discovery of galaxies, so many of the "nebulae" listed in it are really galaxies