Astronomy Final Review

What are refracting telescopes?

A telescope that uses convex lenses to gather and focus lightGalileo's telescopes were refractors, as are today's binoculars and field glasses. However, there is a limit to the size of a refracting telescope (largest is 49 inches)

What is a reflector telescope?

A telescope that uses a large mirror to reflect and focus light.

what is radical velocity?

Doppler effect is produced only by a motion toward or away from the observerSideways motion does not produce such an effect.

what is the dark rift?

which runs lengthwise down a long part of the Milky Way in our sky and appears to split it in two, is produced by a collection of such obscuring clouds.

What direction does the Earth rotate?

the earth rotates toward the east and west is the opposite North & South Poles are Well Defined while East and West are more obsolete

What is longitude? (How do we get it?)

the east-west location the number of degrees along arc from your meridian to the prime meridian in Greenwich England

What is hydrostatic equilibrium?

An analogy is an inflated balloon, which will expand or contract until an equilibrium is reached between the pressure of the air inside and outside. The technical term for this condition is hydrostatic equilibrium. Stable stars are all in hydrostatic equilibrium; so are the oceans of Earth as well as Earth's atmosphere. The air's own pressure keeps it from falling to the ground.

what is the parallax?

An apparent shift in the position of an object when viewed from different locationsTriangulation allows us to measure distances to inaccessible objects. By getting the angle to a tree from two different vantage points, we can calculate the properties of the triangle they make and thus the distance to the tree.

What is the emission spectrum?

appears as a pattern or series of bright lines; it consists of light in which only certain discrete wavelengths are present.

what are infrare rays and where are they observed from?

are absorbed by water and carbon dioxide molecules, which are more concentrated low in Earth's atmosphere.infrared astronomy is best done from high mountaintops, high-flying airplanes, and spacecraft.he nerve endings in our skin are sensitive to this band of the electromagnetic spectrum.

describe the energy levels of ionized atoms

are entirely different from those of the same atom when it is neutral. Each time an electron is removed from the atom, the energy levels of the ion, and thus the wavelengths of the spectral lines it can produce, change.Ionized hydrogen, having no electron, can produce no absorption lines.

what is conduction?

atoms or molecules pass on their energy by colliding with others nearby. This happens, for example, when the handle of a metal spoon heats up as you stir a cup of hot coffee.heat transfer by physical contact during which the energetic motion of particles in one region spread to other regions and even to adjacent objects in close contact

what can the turning of the celestial sphere be attributed to ?

either by a daily rotation of the sky around a stationary Earth or by the rotation of Earth itself

why is the problem with measure even the nearest stars?

parallax angles are usually only a fraction of a second of arc. Recall that one second of arc (arcsec) is an angle of only 1/3600 of a degree. A coin the size of a US quarter would appear to have a diameter of 1 arcsecond if you were viewing it from a distance of about 5 kilometers (3 miles). Think about how small an angle that is.

How can we get nuclei close enough to participate in fusion?

tremendous heat—which speeds the protons up enough to overcome the electrical forces that try to keep protons apart.In the Sun: Two protons can fuse only in regions( like the center where temp is 15 mill K) where the temperature is greater than about 12 million K, and the speed of the protons average around 1000 kilometers per second or more

how do we use a spectrograph to analyze starlight

use a spectrograph to spread out the light into a spectrum

The basic idea of triggered star formation is this:

when a massive star is formed, it emits a large amount of ultraviolet radiation and ejects high-speed gas in the form of a stellar wind. This injection of energy heats the gas around the stars and causes it to expand. When massive stars exhaust their supply of fuel, they explode, and the energy of the explosion also heats the gas. The hot gases pile into the surrounding cold molecular cloud, compressing the material in it and increasing its density. If this increase in density is large enough, gravity will overcome pressure, and stars will begin to form in the compressed gas. Such a chain reaction—where the brightest and hottest stars of one area become the cause of star formation "next door"—seems to have occurred not only in Orion but also in many other molecular clouds.

How does the Sun's favoring one hemisphere translate into making it warmer for us down on the surface of Earth?

when the hemisphere is tilted towards the sun it more gets direct sunlight and is more effective at heating the Earth's surface --> you get longer periods of warming increase in the summer and decrease in the winter In June the Sun is north of the celestial equator and spends more time with those who live in the Northern Hemisphere--> it rises high and is above the horizon for as long as 15 hoursThus not only direct rays but also a longer period of time opposite in the Southern Hemisphere

How long does it take for light to go from earth to the moon & back?

3 seconds Light or radio waves takes 1.3 seconds from earth to moon

What is volume?

Volume is measure of the physical space it occupies (cm ^3/mL)

what is a visual binary?

a binary star system in which both of the stars can be seen with a telescope

what is spectral class?

a classification system for stars based the patterns of lines observed in stellar spectraBecause a star's temperature determines which absorption lines are present in its spectrum, these spectral classes are a measure of its surface temperature. There are seven standard spectral classes.

What is an asterism?

a prominent pattern or group of stars found in a constellation.

What is a refractor

a telescope that uses a lens to collect and focus light.

What stars are part of the Milky Way?

all the stars visible in our night sky

What is Kepler's first law?

the planet's orbit is in the shape of ellipse and not a circle

What are open clusters?

Few hundred to few thousand stars -bright -wide range of ages -about 2% are heavy elements (metal-rich)

what are fixed stars?

stars that maintain fixed patterns in the sky wandering stars --> planets

What did Hipparchus do?

--> photometry began with himhe erected an observatory on the island of Rhodes in the Mediterranean. There he prepared a catalog of nearly 1000 stars that included not only their positions but also estimates of their apparent brightnesses.

What are spring tides?

( Spring tides are approximately the same, whether the Sun and Moon are on the same or opposite sides of Earth, because tidal bulges occur on both sides.When the Moon is at first quarter or last quarter (at right angles to the Sun's direction), the tides produced by the

what are the two functions of the telescope?

(1) to collect the faint light from an astronomical source and (2) to focus all the light into a point or an image.**more light we collect the better we can study objects

What is an exoplanet?

(a planet outside our solar system) orbiting a main-sequence star, and today we know that most stars form with planets.

how does a star form (all steps)?

(a) Dense cores form within a molecular cloud. (b) A protostar with a surrounding disk of material forms at the center of a dense core, accumulating additional material from the molecular cloud through gravitational attraction. (c) A stellar wind breaks out but is confined by the disk to flow out along the two poles of the star. (d) Eventually, this wind sweeps away the cloud material and halts the accumulation of additional material, and a newly formed star, surrounded by a disk, becomes observable. These sketches are not drawn to the same scale. The diameter of a typical envelope that is supplying gas to the newly forming star is about 5000 AU. The typical diameter of the disk is about 100 AU or slightly larger than the diameter of the orbit of Pluto.

Star Layers during and after the Main Sequence??

(a) During the main sequence, a star has a core where fusion takes place and a much larger envelope that is too cold for fusion. (b) When the hydrogen in the core is exhausted (made of helium, not hydrogen), the core is compressed by gravity and heats up. The additional heat starts hydrogen fusion in a layer just outside the core. Note that these parts of the Sun are not drawn to scale.

How to Use a Cepheid to Measure Distance?

(a) Find a cepheid variable star and measure its period. (b) Use the period- luminosity relation to calculate the star's luminosity. (c) Measure the star's apparent brightness. (d) Compare the luminosity with the apparent brightness to calculate the distance.

what types of gas produce continuous spectra?

(formed when a solid or very dense gas gives off radiation) is an array of all wavelengths or colors of the rainbow. A continuous spectrum can serve as a backdrop from which the atoms of much less dense gas can absorb light.When we have a hot, thin gas, each particular chemical element or compound produces its own characteristic pattern of spectral lines—its spectral signature. No two types of atoms or molecules give the same patterns. In other words, each particular gas can absorb or emit only certain wavelengths of the light peculiar to that gas.

how do we detect radial velocity on a spectrum?

(motion toward or away from us) changes by about 13 meters per second with a period of 12 years because of the gravitational pull of Jupiter. This corresponds to about 30 miles per hour, roughly the speed at which many of us drive around town. Detecting motion at this level in a star's spectrum presents an enormous technical challenge, but several groups of astronomers around the world, using specialized spectrographs designed for this purpose, have succeeded. Note that the change in speed does not depend on the distance of the star from the observer. Using the Doppler effect to detect planets will work at any distance, as long as the star is bright enough to provide a good spectrum and a large telescope is available to make the observations

The strongest four lines seen at spectral type A1....

(one in the red, one in the blue-green, and two in the blue) are Balmer lines of hydrogen. Note how these lines weaken at both higher and lower temperatures, as Figure 17.5 also indicates. The strong pair of closely spaced lines in the yellow in the cool stars is due to neutral sodium (one of the neutral metals in Figure 17.5).

Why is the apparent solar time not convenient?

, it is not really very convenient to use. The exact length of an apparent solar day varies slightly during the year. The eastward progress of the Sun in its annual journey around the sky is not uniform because the speed of Earth varies slightly in its elliptical orbit. Another complication is that Earth's axis of rotation is not perpendicular to the plane of its revolution. --> does not advance at a uniform rate.

What are eclipsing binary stars?

- Two close stars that appear to be a single star varying in brightnessSome binary stars are lined up in such a way that, when viewed from Earth, each star passes in front of the other during every revolution (Figure 18.10). When one star blocks the light of the other, preventing it from reaching Earth, the luminosity of the system decreases, and astronomers say that an eclipse has occurred.

why is a discrepancy of Earth neutrinos and Sun's neutrino's?

- three types of neutrinos-Solar fusion produces only one type of neutrino, the so-called electron neutrino, and the initial experiments to detect solar neutrinos were designed to detect this one type. Subsequent experiments showed that these neutrinos change to a different type during their journey from the center of the Sun through space to Earth in a process called neutrino oscillation.An experiment, conducted at the Sudbury Neutrino Observatory in Canada, was the first one designed to capture all three types of neutrinos (Figure 16.20). The experiment was located in a mine 2 kilometers underground. The neutrino detector consisted of a 12-meter-diameter transparent acrylic plastic sphere, which contained 1000 metric tons of heavy water. Remember that an ordinary water nucleus contains two hydrogen atoms and one oxygen atom. Heavy water instead contains two deuterium atoms and one oxygen atom, and incoming neutrinos can occasionally break up the loosely bound proton and neutron that make up the deuterium nucleus. The sphere of heavy water was surrounded by a shield of 1700 metric tons of very pure water, which in turn was surrounded by 9600 photomultipliers, devices that detect flashes of light produced after neutrons interact with the heavy water.

What are Johannes Kepler's contributions?

--> agreed with Copernicus's view of the world --> came up with three laws of planetary motion

what does telescope ability to show fine detail depend on

--> aperture-->depends upon the wavelength of the radiation that the telescope is gathering.------>The longer the waves, the harder it is to resolve fine detail in the images or maps we make.------->because radio waves have long wavelengths poses a challenge for good resolution

When does fission occur?

--> atomic bombs--> nuclear reactors-->occurs spontaneously in some unstable nuclei through the process of natural radioactivity.-->fission requires big, complex nuclei, whereas we know that the stars are made up predominantly of small, simple nuclei--> fusion to explain the energy of the Sun & the stars

how do we know that sun is actually this hot ?

--> calculates the temperature and pressure at every point inside the Sun and determines what nuclear reactions, if any, are taking place. For some calculations, we can use observations to determine whether the computer program is producing results that match what we see.-->can also calculate how the Sun will change with time. After all, the Sun must change. In its center, the Sun is slowly depleting its supply of hydrogen and creating helium instead. Will the Sun get hotter? Cooler? Larger? Smaller? Brighter? Fainter?-->changes in center: since eventually all the hydrogen fuel hot enough for fusion will be exhausted. Either a new source of energy must be found, or the Sun will cease to shine.

Explain Newton's Universal Law of Gravitation?

--> the nature state of motion is in a straight line but planets move in a ellipse so some force must be bending them into this path -->Gravity was only a concept related to Earth--> extended it to moon --> all material bodies, so attractive force between the Sun and each of the planets could keep them in orbit Mathematical Model:Fgravity = G(M1 M2)/ R2 --> universal law of gravitationObjects accelerate downward at 9.8 meters per second on earth

what is a neutrino?

-->Energy seemed to disappear when certain types of nuclear reactions took place, violating the law of conservation of energy.-->a so-far-undetected particle, which was given the name neutrino carried away the "missing" energy.-->neutrinos were particles with zero mass, and that like photons, they moved with the speed of light.

what is proper motion?

-->cannot be detected with stellar spectra-->, we do not notice any change in the positions of the bright stars during the course of a human lifetime-->which is along our line of sight (i.e., toward or away from Earth), this motion, called proper motion, is transverse: that is, across our line of sight. We see it as a change in the relative positions of the stars on the celestial sphere (Figure 17.11). These changes are very slow. Even the star with the largest proper motion takes 200 years to change its position in the sky by an amount equal to the width of the full Moon, and the motions of other stars are smaller yet.

why is contraction not the primary source of solar energy?

-->sun is much older than 100 million years-->contraction is an important source of energy while stars are being born

what happens when light atomic nuclei come together to form a heavier one or vice versa?

--What this means is that, in general, when light atomic nuclei come together to form a heavier one (up to iron), mass is lost and energy is released.This joining together of atomic nuclei is called nuclear fusion.-->Energy can also be produced by breaking up heavy atomic nuclei into lighter ones (down to iron); this process is called nuclear fission

what is maxwell's theory of electromagnetism?

-deals with the electrical charge of subatomic particles and their effect; especially when they are moving-When charges are not in motion, we observe only this electric attraction or repulsion. If charges are in motion, however (as they are inside every atom and in a wire carrying a current), then we measure another force called magnetism

what happens in the atoms inside as a degenerate star cools?

. Calculations show that as a degenerate star cools, the atoms inside it in essence "solidify" into a giant, highly compact lattice (organized rows of atoms, just like in a crystal). When carbon is compressed and crystallized in this way, it becomes a giant diamond-like star.

What are x-rays and where are they observed from?

.01 to 20 nanometerscan penetrate a short length of human flesh, they are stopped by the large numbers of atoms in Earth's atmosphere with which they interact.also can only study in space

What stops the tides from being as strong as they can be?

.However, the presence of land masses stopping the flow of water, the friction in the oceans and between oceans and the ocean floors, the rotation of Earth, the wind, the variable depth of the ocean, and other factors all complicate the picture. --> some places have small tides and some have high tides one set of tide predictions doesn't work for the whole planet.

what are the three basic components of a modern system for measuring radiation from astronomical sources.

1. telescope: serves as a "bucket" for collecting visible light (or radiation at other wavelengths, as shown2. wavelength sorting device: attached to the telescope that sorts the incoming radiation by wavelength (we might simply want to separate blue light from red light so that we can determine the temperature of a star. But at other times, we want to see individual spectral lines to determine what an object is made of, or to measure its speed)3. Detector: a device that senses the radiation in the wavelength regions we have chosen and permanently records the observations.

what are the distinct characteristics of waves generated by charged particles

1.electromagnetic waves do not require water or air: the fields generate each other and so can move through a vacuum (such as outer space).--->19th century scientists made aehter- something that fils space so em waves have some medium through which they move 2.all electromagnetic waves move at the same speed in empty space--> speed of light 3*10^8 m/s--> no matter what they move at this fastest possible speed--> we perceive differences as color

what are the properties of light?

1.light can be reflected from a surface. 2.Light is also bent, or refracted, when it passes from one kind of transparent material into another—say, from the air into a glass lens.

what determines how good resolution is?

1.size of the telescope.Larger apertures produce sharper images

How long does it take for light to travel 1 Astronomical Unit?

8 minutes

why is fusion unsustainable on Earth?

= cannot be controlled=Fusion energy would have many advantages: it would use hydrogen (or deuterium, which is heavy hydrogen) as fuel, and there is abundant hydrogen in Earth's lakes and oceans. Water is much more evenly distributed around the world than oil or uranium, meaning that a few countries would no longer hold an energy advantage over the others. And unlike fission, which leaves dangerous byproducts, the nuclei that result from fusion are perfectly safe.=HOWEVER,it takes extremely high temperatures for nuclei to overcome their electrical repulsion and undergo fusion.-Interactions at such temperatures are difficult to sustain and control.

what is a giant star?

A giant star has a large, extended photosphere. Because it is so large, a giant star's atoms are spread over a great volume, which means that the density of particles in the star's photosphere is low. As a result, the pressure in a giant star's photosphere is also low.

whats the difference between spectral lines of a giant star vs a small star?

A giant star with a very-low-pressure photosphere shows very narrow spectral lines (bottom), whereas a smaller star with a higher- pressure photosphere shows much broader spectral lines (top).

what is supernova?

A gigantic explosion in which a massive star collapses and throws its outer layers into spaceWhen these explosions happen close by, they can be among the most spectacular celestial events, as we will discuss in the next section. (Actually, there are at least two different types of supernova explosions: the kind we have been describing, which is the collapse of a massive star, is called, for historical reasons, a type II supernova. We will describe how the types differ later in this chapter).

how do you use spectrum to determine stellar rotation?

A rotating star will show broader spectral lines than a nonrotating star.Figure 17.14

What are the Lyman series

A set of spectral lines that appear in the UV region when a hydrogen atom undergoes a transition from energy levels n>1 to n=

What do we mean, exactly, by "discovery" of transiting exoplanets?

A single transit shows up as a very slight drop in the brightness of the star, lasting several hours. However, astronomers must be on guard against other factors that might produce a false transit, especially when working at the limit of precision of the telescope. We must wait for a second transit of similar depth. But when another transit is observed, we don't initially know whether it might be due to another planet in a different orbit. The "discovery" occurs only when a third transit is found with similar depth and the same spacing in time as the first pair.

Compare the solar and sidereal day? What were the implications of the solar day?

A solar day is slightly longer than a sidereal day because Earth not only turns but also moves along its path around the Sun in a day When Earth has completed one rotation with respect to the distant star and is at day 2, the long arrow again points to the same distant star. However, notice that because of the movement of Earth along its orbit from day 1 to 2, the Sun has not yet reached a position above the observer. To complete a solar day, Earth must rotate an additional amount, equal to 1/365 of a full turn. The time required for this extra rotation is 1/365 of a day, or about 4 minutes. So the solar day is about 4 minutes longer than the sidereal day.Because our ordinary clocks are set to solar time, stars rise 4 minutes earlier each day. Astronomers prefer sidereal time for planning their observations because in that system, a star rises at the same time every day.

what is spectroscopic binary?

A star like Mizar A, which appears as a single star when photographed or observed visually through the telescope, but which spectroscopy shows really to be a double star

what are adaptive optics?

A technique in which telescope mirrors flex rapidly to compensate for the bending of starlight caused by atmospheric turbulence-->most effective in the infrared region of the spectrum

H-R Diagrams of Older Clusters

After 4 billion years have passed, many more stars, including stars that are only a few times more massive than the Sun, have left the main sequence (Figure 22.13). This means that no stars are left near the top of the main sequence; only the low-mass stars near the bottom remain. The older the cluster, the lower the point on the main sequence (and the lower the mass of the stars) where stars begin to move toward the red giant region.

As clusters get older, their H-R diagrams begin to change.....

After a short time (less than a million years after they reach the main sequence), the most massive stars use up the hydrogen in their cores and evolve off the main sequence to become red giants and supergiants. As more time passes, stars of lower mass begin to leave the main sequence and make their way to the upper right of the H-R diagram

what happens quickly and then what happens slowly?

After the deuterium nucleus is formed, it survives an average of only about 6 seconds before being converted into 3He. About a million years after that (on average), the 3He nucleus will combine with another to form 4He

what happens to stars with mass 150 Msun and greater?

After the helium in its core is exhausted (see The Evolution of More Massive Stars), the evolution of a massive star takes a significantly different course from that of lower-mass stars. In a massive star, the weight of the outer layers is sufficient to force the carbon core to contract until it becomes hot enough to fuse carbon into oxygen, neon, and magnesium. This cycle of contraction, heating, and the ignition of another nuclear fuel repeats several more times. After each of the possible nuclear fuels is exhausted, the core contracts again until it reaches a new temperature high enough to fuse still-heavier nuclei. The products of carbon fusion can be further converted into silicon, sulfur, calcium, and argon. And these elements, when heated to a still-higher temperature, can combine to produce iron. Massive stars go through these stages very, very quickly. In really massive stars, some fusion stages toward the very end can take only months or even days! This is a far cry from the millions of years they spend in the main-sequence stage.

explain the electromagnetic radiation

All of the frequencies or wavelengths of electromagnetic radiation

what is absorption?

Although gas does not absorb much light, we know from everyday experience that tiny solid or liquid particles can be very efficient absorbers. Water vapor in the air is quite invisible. When some of that vapor condenses into tiny water droplets, however, the resulting cloud is opaque. Dust storms, smoke, and smog offer familiar examples of the efficiency with which solid particles absorb light. On the basis of arguments like these, astronomers have concluded that widely scattered solid particles in interstellar space must be responsible for the observed dimming of starlight.

Explain what could cause the eclipses of the moon (what about the sun and moon position allows it?)

Although the Sun is about 400 times larger in diameter than the Moon, it is also about 400 times farther away, so both the Sun and the Moon have the same angular size—about 1/2°When the Moon's shadow strikes Earth, people within that shadow see the Sun at least partially covered by the Moon; that is, they witness a solar eclipse.When the Moon passes into the shadow of Earth, people on the night side of Earth see the Moon darken in what is called a lunar eclipse.The shadows of Earth and the Moon consist of two parts: a cone where the shadow is darkest, called the umbra, and a lighter, more diffuse region of darkness called the penumbra.As you can imagine, the most spectacular eclipses occur when an object enters the umbra.

what causes stars to form?

Although we do not know what initially caused stars to begin forming in Orion, there is good evidence that the first generation of stars triggered the formation of additional stars, which in turn led to the formation of still more stars

what is the excitation?

An atom can absorb energy, which raises it to a higher energy level (corresponding, in the simple Bohr picture, to an electron's movement to a larger orbit)Generally, an atom remains excited for only a very brief time. After a short interval, typically a hundred-millionth of a second or so, it drops back spontaneously to its ground state, with the simultaneous emission of lightWith each jump, it emits a photon of the wavelength that corresponds to the energy difference between the levels at the beginning and end of that jump

What is the nearest galaxy that is a spiral ?

Andromeda Galaxy

what can be used as radar telescope?

Any radio dish can be used as a radar telescope if it is equipped with a powerful transmitter as well as a receiver.largest radar telescope 1000-foot (305-meter) telescope at Arecibo in Puerto Rico

why is the end of all fusion reactions the end of a star's death?

As the core is stabilized by degeneracy pressure, a last shudder of fusion passes through the outside of the star, consuming the little hydrogen still remaining. Now the star is a true white dwarf: nuclear fusion in its interior has ceased

what are planet transits?

As the planet transits, it blocks out some of the light from the star, causing a temporary dimming in the brightness of the star. The top figure shows three moments during the transit event and the bottom panel shows the corresponding light curve: (1) out of transit, (2) transit ingress, and (3) the full drop in brightness.

why is all directions on a spinning sphere are not created equal Why?

As the protostar rotates, it is much easier for material to fall right onto the poles (which spin most slowly) than onto the equator (where material moves around most rapidly). Therefore, gas and dust falling in toward the protostar's equator are "held back" by the rotation and form a whirling extended disk around the equator (part b in Figure 21.8). You may have observed this same "equator effect" on the amusement park ride in which you stand with your back to a cylinder that is spun faster and faster. As you spin really fast, you are pushed against the wall so strongly that you cannot possibly fall toward the center of the cylinder. Gas can, however, fall onto the protostar easily from directions away from the star's equator

What is the difference between asteroid and comet?

Asteroids have orbits with smaller semimajor axes than do comets ( majority lie between 2.2 & 3.3 AUAsteroid belt is in the middle of Mars and Jupiter--> b/c they are so far apartComets generally have orbits of larger size & greater eccentricity than those of the asteroids--> .8 eccentricity of higherThey spend most of their time far away from Sun moving very slowly, as they approach perihelion--> comets stepped up and whip through inner parts of orbit faster

What were the changes/implications made after the discovery of refraction?

At equinoxes sun above the horizon for a little longer than 12 hours and & below for a little less than 12Most dramatic at the poles--> more than a week before it reaches the equatorWarmer and colder are a little after the times when we get the most/least sunlight because it takes time for Earth to warm up

What is the focus?

At the focus, an image of the light source appears. In the case of parallel light rays, the distance from the lens to the location where the light rays focus, or image, behind the lens is called the focal length of the lens.

what happens at the every end to these massive stars?

At this stage of its evolution, a massive star resembles an onion with an iron core. As we get farther from the center, we find shells of decreasing temperature in which nuclear reactions involve nuclei of progressively lower mass—silicon and sulfur, oxygen, neon, carbon, helium, and finally, hydrogen

What is a solar day?

Basic unit of time = daySolar day: rotation period of Earth with respect to the Sun--> set our clocks to sun time

why are CCDs the better option?

Because CCDs typically record as much as 60-70% of all the photons that strike them, and the best silicon and infrared CCDs exceed 90% sensitivity, we can detect much fainter objects.CDs also provide more accurate measurements of the brightness of astronomical objects than photography, and their output is digital—in the form of numbers that can go directly into a computer for analysis.

why are there many molecular clouds that form only low mass stars?

Because low-mass stars do not have strong winds and do not die by exploding, triggered star formation cannot occur in these clouds. There are also stars that form in relative isolation in small cores. Therefore, not all star formation is originally triggered by the death of massive stars. However, there are likely to be other possible triggers, such as spiral density waves and other processes we do not yet understand

Why use a color index if it ultimately implies temperature?

Because the brightness of a star through a filter is what astronomers actually measure, and we are always more comfortable when our statements have to do with measurable quantities.

why do telescopes designed with mirrors avoid the problems of refracting telescopes?

Because the light is reflected from the front surface only, flaws and bubbles within the glass do not affect the path of the light. In a telescope designed with mirrors, only the front surface has to be manufactured to a precise shape, and the mirror can be supported from the back.

Why do we not feel the earth moving?

Because we are bound by gravity bound to the earth and there is no resistance to Earth's motion in a vacuum we don't feel the fast moving pace of earth

how did we discover Ultra-Hot Interstellar Gas?

Before the launch of astronomical observatories into space, which could see radiation in the ultraviolet and X-ray parts of the spectrum, astronomers assumed that most of the region between stars was filled with hydrogen at temperatures no warmer than those found in H II regions. But telescopes launched above Earth's atmosphere obtained ultraviolet spectra that contained interstellar lines produced by oxygen atoms that have been ionized five times.

what does color indicate about temperature?

Blue 25000kWhite 10000kYellow 6000kOrange 4000kRed 3000kThe hottest stars have temperatures of over 40,000 K, and the coolest stars have temperatures of about 2000 K. Our Sun's surface temperature is about 6000 K; its peak wavelength color is a slightly greenish-yellow. In space, the Sun would look white, shining with about equal amounts of reddish and bluish wavelengths of light. It looks somewhat yellow as seen from Earth's surface because our planet's nitrogen molecules scatter some of the shorter (i.e., blue) wavelengths out of the beams of sunlight that reach us, leaving more long wavelength light behind. This also explains why the sky is blue: the blue sky is sunlight scattered by Earth's atmosphere.

describe Ernest Rutherford's experiment?

Bombarded a thin piece of gold foil with a stream of alpha particlesMost of these particles passed through the gold foil just as if the atoms in it were nearly empty space 1/8000 bounced back and reversed direction from the foil

temperature and density in the inner region??

Calculations show that the temperature and density in the inner region slowly increase as helium accumulates in the center of a star. As the temperature gets hotter, each proton acquires more energy of motion on average; this means it is more likely to interact with other protons, and as a result, the rate of fusion also increases. For the proton-proton cycle described in, the rate of fusion goes up roughly as the temperature to the fourth power.If the rate of fusion goes up, the rate at which energy is being generated also increases, and the luminosity of the star gradually rises. Initially, however, these changes are small, and stars remain within the main-sequence band on the H-R diagram for most of their lifetimes.

what is an interferometer?

Collection of two or more telescopes working together as a team, observing the same object at the same time and at the same wavelength. The effective diameter of an interferometer is equal to the distance between its outermost telescopes.recent advances make it possible to do interferometry at visible-light and infrared wavelengths.

how did people originally measure distance within the solar system?

Copernicus and Kepler established the relative distances of the planets-->couldn't establish absolute distances, to establish absolute distances, astronomers-->had to measure one distance in the solar system directly.--> measured estimate of Venus

formula for estimating mass of binary stars?

D^3 = (M1 + M2)P^2where D is in astronomical units, P is measured in years, and M1 + M2 is the sum of the masses of the two stars in units of the Sun's mass. This is a very useful formula for astronomers; it says that if we can observe the size of the orbit and the period of mutual revolution of the stars in a binary system, we can calculate the sum of their masses.Most spectroscopic binaries have periods ranging from a few days to a few months, with separations of usually less than 1 AU between their member stars.

Why couldn't it be the interstellar gas that reddens distant stars and not the dust?

Despite its very high density compared with that of interstellar gas, it is so transparent as to be practically invisible. (Gas does have a few specific spectral lines, but they absorb only a tiny fraction of the light as it passes through.)The quantity of gas required to produce the observed absorption of light in interstellar space would have to be enormous. The gravitational attraction of so great a mass of gas would affect the motions of stars in ways that could easily be detected. Such motions are not observed, and thus, the interstellar absorption cannot be the result of gases.

how does matter turn into energy?

E= mc^2 energy, mass, speed of light (3 * 10^8 m/s)he factor of c2 is just the number that Einstein showed must be used to relate mass and energy.--> conversion of even small mass results in a lot of energy--> this conversion is the source of the Sun's light and heat

how do the light look when it reaches the telescope ?

Each light beam path will be slightly different, and each will reach the detector of the telescope at a slightly different place. The result is a blurred image, and because the cells are being blown by the wind, the nature of the blur will change many times each second.

how are the spectral classes divided?

Each of these spectral classes, except possibly for the Y class which is still being defined, is further subdivided into 10 subclasses designated by the numbers 0 through 9. A B0 star is the hottest type of B star; a B9 star is the coolest type of B star and is only slightly hotter than an A0 star.

why are observations outside of earth better?

Earth's atmosphere blocks most radiation at wavelengths shorter than visible light, so we can only make direct ultraviolet, X-ray, and gamma ray observations from space (though indirect gamma ray observations can be made from Earth). Getting above the distorting effects of the atmosphere is also an advantage at visible and infrared wavelengthsamount of detail you can observe is limited only by the size of the instrument & the cost

What are line of nodes and how do they help causes eclipses?

Eclipses can only occur twice per year when the "line of nodes" points towards the Sun. If the Moon happens to be Full or New at those times →Eclipse!

What is astronomy around the world?

Egyptians: adopted a calendar 365 days and kept track of Sirius because this cycle corresponds with the Nile RiverChinese determined the same year length + comets, meteors and dark spots on the SunRecorded guest stars that are usually invisible but sometimes brighten up for a little time --> still use these records Mayan Culture in Mexico and Central America --> calendar based on Venus and made observations from site dedicated to this causePolynesians learned to navigate by the stars over hundreds of kilometers of open oceanBritain people used stone circles to track of motions of the sun and moon > Stonehedge Eastern Mediterranean knew Earth was round --> stemmed from Pythagoras that said perfect forms came in shapes of circles and spheres so Earth must be roundGreeks = gods likes spheres hence moon is round

what is the model of the sun?

Energy is generated through fusion in the core of the Sun, which extends only about one-quarter of the way to the surface but contains about one-third of the total mass of the Sun. At the center, the temperature reaches a maximum of approximately 15 million K, and the density is nearly 150 times that of water. The energy generated in the core is transported toward the surface by radiation until it reaches a point about 70% of the distance from the center to the surface. At this point, convection begins, and energy is transported the rest of the way, primarily by rising columns of hot gas.

what is newton's first law and interpretation of this law?

Every object will continue to be in a state of rest or move at a constant speed in a straight line unless it is compelled to change by an outside force. --> conservation of momentum In the absence of any outside influence, there is a measure of a body's motion, called its momentum, that remains unchanged --> law of inertia

What is magnetism?

Experiments with electric charges demonstrated that magnetism was the result of moving charged particles.-sometimes motion is clear and sometimes more subtle,- as in the kind of magnet you buy in a hardware store, in which many of the electrons inside the atoms are spinning in roughly the same direction; it is the alignment of their motion that causes the material to become magnetic.

what are the advantage for infrared observations from space?

First is the elimination of all interference from the atmosphere.Equally important is the opportunity to cool the entire optical system of the instrument in order to nearly eliminate infrared radiation from the telescope itself.

What is the Gregorian Calendar?

First, 10 days had to be dropped out of the calendar to bring the vernal equinox back to March 21; by proclamation, the day following October 4, 1582, became October 15The second feature of the new Gregorian calendar was a change in the rule for leap year, making the average length of the year more closely approximate the tropical year. Gregory decreed that three of every four century years—all leap years under the Julian calendar— (1600,2000)The average length of this Gregorian year, 365.2425 mean solar days, is correct to about 1 day in 3300 years.

what is the max for refracting telescope?

George Halle realized that 40 inches was close to the maximum feasible aperture for refracting telescopes.-> larger apertures = reflecting telescopes--> set out to construct 60 in reflector

What is the amount of daylight in September and March ? (where is the sun?)

Halfway between the solstices, on about March 21 and September 21, the Sun is on the celestial equator. From Earth, it appears above our planet's equator and favors neither hemisphere. Every place on Earth then receives roughly 12 hours of sunshine and 12 hours of night. The points where the Sun crosses the celestial equator are called the vernal (spring) and autumnal (fall) equinoxes.

What is magnitude?

He referred to the brightest stars in his catalog as first-magnitudes stars, whereas those so faint he could barely see them were sixth-magnitude stars.

How was Neptune discovered?

Herschel --> Uranus 1781--> some planets could be too dim to visible to naked eyeEven after allowance for perturbations was made for Uranus, there was a .03 degree difference in predicted vs actual--> Couch Adams proposed another planet and told George Airy where to find the new planet in the skyVerrier published it--> airy told Challis to search for new object -->Challis was going to repeatedly observe faint stars over multiple day and hoped the planet would distinguish itself from stars based on motion--> failed to do soVerrier -> Galle + possessing new charts of the Aquarius region, found and identified the planet that very night. It was less than a degree from the position Le verrier predictedDiscovery of Neptune (Adams & Le Verrier) was a triumph for gravitational theory for it dramatically confirmed the generality of Newton's laws

what happens when hot stars are nearby gas?

Hot stars are able to heat nearby gas to temperatures close to 10,000 K. The ultraviolet radiation from the stars also ionizes the hydrogen (remember that during ionization, the electron is stripped completely away from the proton). Such a detached proton won't remain alone forever when attractive electrons are around; it will capture a free electron, becoming a neutral hydrogen once more. However, such a neutral atom can then absorb ultraviolet radiation again and start the cycle over.At a typical moment, most of the atoms near a hot star are in the ionized state.

What holds the atom together?

Hydrogen simplest atomMass of electron is 2000x smaller than the mass of a protonElectromagnetic force that holds proton and lector's together, just as gravity is the force that keep planets in orbit around the sun as protons increase the ratio of proton to neutrons goes up

why is stellar spectra not based on chemical composition of stars?

Hydrogen, for example, is by far the most abundant element in most stars. However, lines of hydrogen are not seen in the spectra of the hottest and the coolest stars. In the atmospheres of the hottest stars, hydrogen atoms are completely ionized. Because the electron and the proton are separated, ionized hydrogen cannot produce absorption lines.In the atmospheres of the coolest stars, hydrogen atoms have their electrons attached and can switch energy levels to produce lines. However, practically all of the hydrogen atoms are in the lowest energy state (unexcited) in these stars and thus can absorb only those photons able to lift an electron from that first energy level to a higher level. Photons with enough energy to do this lie in the ultraviolet part of the electromagnetic spectrum, and there are very few ultraviolet photons in the radiation from a cool star.What this means is that if you observe the spectrum of a very hot or very cool star with a typical telescope on the surface of Earth, the most common element in that star, hydrogen, will show very weak spectral lines or none at al

how would u look at a new model today?

Hypothesis proposed has be checked with what's already known --> heliocentric theory passes this test, planetary positions as well as geocentricDetermine which predictions the new hypothesis makes that differ from these if competing ideas

What are the luminosity classes?

Ia: Brightest supergiantsIb: Less luminous supergiantsII: Bright giantsIII: GiantsIV: Subgiants (intermediate between giants and main-sequence stars)V: Main-sequence stars

how do we use doppler effect to measure stars rotation?

If an object is rotating, then one of its sides is approaching us while the other is receding (unless its axis of rotation happens to be pointed exactly toward us). This is clearly the case for the Sun or a planet; we can observe the light from either the approaching or receding edge of these nearby objects and directly measure the Doppler shifts that arise from the rotation.

What happens if the sun & moon are properly aligned?

If the Sun and Moon are properly aligned, then the Moon's darkest shadow intersects the ground at a small point on Earth's surface. Anyone on Earth within the small area covered by the tip of the Moon's shadow will, for a few minutes, be unable to see the Sun and will witness a total eclipse.observers on a larger area of Earth's surface who are in the penumbra will see only a part of the Sun eclipsed by the Moon: we call this a partial solar eclipse.Between Earth's rotation and the motion of the Moon in its orbit, the tip of the Moon's shadow sweeps eastward at about 1500 kilometers per hour along a thin band across the surface of Earth.The thin zone across Earth within which a total solar eclipse is visible (weather permitting) is called the eclipse path.Within a region about 3000 kilometers on either side of the eclipse path, a partial solar eclipse is visible. It does not take long for the Moon's shadow to sweep past a given point on Earth. The duration of totality may be only a brief instant; it can never exceed about 7 minutes.

why does an object at a higher temp emit more power at wavelength than does a cooler one?

In a hot gas, for example, the atoms have more collisions and give off more energy. In the real world of stars, this means that hotter stars give off more energy at every wavelength than do cooler stars

If we can observe the spectrum of a star, we can estimate

If we can observe the spectrum of a star, we can estimate its distance from our understanding of the H-R diagram. As discussed in Analyzing Starlight, a detailed examination of a stellar spectrum allows astronomers to classify the star into one of the spectral types indicating surface temperature. (The types are O, B, A, F, G, K, M, L, T, and Y; each of these can be divided into numbered subgroups.) In general, however, the spectral type alone is not enough to allow us to estimate luminosity.BUTTT . A G2 star could be a main- sequence star with a luminosity of 1 LSun, or it could be a giant with a luminosity of 100 LSun, or even a supergiant with a still higher luminosity.

how do multiple bodies in space interact and how do we find out the motion of a single one?

If you have a cluster and you know the position of each start at any given instant you can calculate the combined gravitational force of the entire group on any one member of the clusteryou can find how will accelerate--> thus tracking its motionwe must simultaneously calculate the acceleration of each star produced by the combination of the gravitational attractions of all of all others in order to track the motions of all of them and hence of any oneThe dominant gravitational attraction of the Sun --> on orbit of planets--> treat the effects of other bodies as small perturbations (disturbances)--> lead to discovery of new planet in 1846

How the position relative to poles determine what you see in the sky?

If you on the north pole you only see half the sky north of the celestial equator and never in the south and vice versa if you are in the south pole where the latitude is 38° N, the north celestial pole is 38° above the northern horizon &he south celestial pole is 38° below the southern horizon and, thus, never visible

why doesn't this reemitted light quickly "fill in" the darker absorption lines?

Imagine a beam of white light coming toward you through some cooler gas. Some of the reemitted light is actually returned to the beam of white light you see, but this fills in the absorption lines only to a slight extent. The reason is that the atoms in the gas reemit light in all directions, and only a small fraction of the reemitted light is in the direction of the original beam (toward you). In a star, much of the reemitted light actually goes in directions leading back into the star, which does observers outside the star no good whatsoeve

interiors of rocky planets make the simplifying assumption that the planet consists of two or three layers.

In Figure 21.25, the two green triangles with roughly 1 MEarth and 1 REarth represent Venus and Earth. Notice that these planets fall between the models for a pure iron and a pure rock planet, consistent with what we would expect for the known mixed-chemical composition of Venus and Earth.In the case of gaseous planets, the situation is more complex. Hydrogen is the lightest element in the periodic table, yet many of the detected exoplanets in Figure 21.25 with masses greater than 100 MEarth have radii that suggest they are lower in density than a pure hydrogen planet. Hydrogen is the lightest element, so what is happening here? Why do some gas giant planets have inflated radii that are larger than the fictitious pure hydrogen planet? Many of these planets reside in short-period orbits close to the host star where they intercept a significant amount of radiated energy. If this energy is trapped deep in the planet atmosphere, it can cause the planet to expand.Planets that orbit close to their host stars in slightly eccentric orbits have another source of energy: the star will raise tides in these planets that tend to circularize the orbits. This process also results in tidal dissipation of energy that can inflate the atmosphere. It would be interesting to measure the size of gas giant planets in wider orbits where the planets should be cooler—the expectation is that unless they are very young, these cooler gas giant exoplanets (sometimes called "cold Jupiters") should not be inflated. But we don't yet have data on these more distant exoplanets.

how do photographic plates work?

In a photographic plate, a light-sensitive chemical coating is applied to a piece of glass that, when developed, provides a lasting record of the image. At observatories around the world, vast collections of photographs preserve what the sky has looked like during the past 100 years.

what is the prime focus?

In a reflecting telescope, the concave mirror is placed at the bottom of a tube or open framework. The mirror reflects the light back up the tube to form an image near the front end at a location called the prime focus.Since an astronomer at the primer focus can block much of the light coming to the main mirror, the use of a small secondary mirror allows more light to get through the system

individual stars in an open cluster can survive for billions of years, they typically remain together as a cluster for only a few million years, or at most, a few hundred million years.WHY?

In small open clusters, the average speed of the member stars within the cluster may be higher than the cluster's escape velocity,[1] and the stars will gradually "evaporate" from the cluster. Close encounters of member stars may also increase the velocity of one of the members beyond the escape velocity. Every few hundred million years or so, the cluster may have a close encounter with a giant molecular cloud, and the gravitational force exerted by the cloud may tear the cluster apart.

what do the outflows from the proto stars cause?

In the HH47 image, a protostar 1500 light-years away (invisible inside a dust disk at the left edge of the image) produces a very complicated jet. The star may actually be wobbling, perhaps because it has a companion. Light from the star illuminates the white region at the left because light can emerge perpendicular to the disk (just as the jet does). At right, the jet is plowing into existing clumps of interstellar gas, producing a shock wave that resembles an arrowhead

what is reddening?

In the early part of the twentieth century, astronomers discovered that some stars look red even though their spectral lines indicate that they must be extremely hot (and thus should look blue). The solution to this seeming contradiction turned out to be that the light from these hot stars is not only dimmed but also reddened by interstellar dust, a phenomenon known as interstellar reddening.

describe Barnard 68 in Infrared.

In this image, the red color shows radiation emitted in the infrared at a wavelength of 2.2 microns. Interstellar extinction is much smaller at infrared than at visible wavelengths, so the stars behind the cloud become visible in the infrared channel.

what happens to the white dwarf in this binary system?

In this way, the white dwarf quickly (but only briefly) becomes quite bright, hundreds or thousands of times its previous luminosity.

What is the Keck telescope?

Instead of a single primary mirror 10 meters in diameter, each Keck telescope achieves its larger aperture by combining the light from 36 separate hexagonal mirrors, each 1.8 meters wide (Figure 6.9).Computer-controlled actuators (motors) constantly adjust these 36 mirrors so that the overall reflecting surface acts like a single mirror with just the right shape to collect and focus the light into a sharp image.--> steel structure designed so entire telescope can be pointed toward anywhere on the sky--> motorized drive system that moves it very smoothly from east to west at exactly the same rate that Earth is rotating from west to east, so it can continue to point at the object being observed.->housed in a dome to protect elements and moved so light from objected isn't blocked

What are the interstellar clouds lifetime?

Interstellar clouds do not last for the lifetime of the universe. Instead, they are like clouds on Earth, constantly shifting, merging with each other, growing, or dispersing. Some become dense and massive enough to collapse under their own gravity, forming new stars. When stars die, they, in turn, eject some of their material into interstellar space. This material can then form new clouds and begin the cycle over again.

describe the Scattering of Light by Dust.

Interstellar dust scatters blue light more efficiently than red light, thereby making distant stars appear redder and giving clouds of dust near stars a bluish hue. Here, a red ray of light from a star comes straight through to the observer, whereas a blue ray is shown scattering. A similar scattering process makes Earth's sky look blue.

what about binary stars in which neutron stars have companions?

It is possible that, under the right circumstances, a binary system can even survive the explosion of one of its members as a type II supernova. In that case, an ordinary star can eventually share a system with a neutron star. If material is then transferred from the "living" star to its "dead" (and highly compressed) companion, this material will be pulled in by the strong gravity of the neutron star. Such infalling gas will be compressed and heated to incredible temperatures. It will quickly become so hot that it will experience an explosive burst of fusion. The energies involved are so great that we would expect much of the radiation from the burst to emerge as X-rays. And indeed, high-energy observatories above Earth's atmosphere (see Astronomical Instruments) have recorded many objects that undergo just these types of X-ray bursts.

what is the easiest way to measure diameter of the sun?

Its angular diameter—that is, its apparent size on the sky—is about 1/2°. If we know the angle the Sun takes up in the sky and how far away it is, we can calculate its true (linear) diameter, which is 1.39 million kilometers, or about 109 times the diameter of Earth.**CANT DO IT For other stars they are too far away

describe the Structure of an Old Massive Star

Just before its final gravitational collapse, the core of a massive star resembles an onion. The iron core is surrounded by layers of silicon and sulfur, oxygen, neon, carbon mixed with some oxygen, helium, and finally hydrogen. Outside the core, the composition is mainly hydrogen and helium. (Note that this diagram is not precisely to scale but is just meant to convey the general idea of what such a star would be like.) (credit: modification of work by ESO, Digitized Sky Survey)

what about gravity as a source of energy?

Kelvin & Helmholtz-->Sun might produce energy by the conversion of gravitational energy into heatThey suggested that the outer layers of the Sun might be "falling" inward because of the force of gravity. In other words, they proposed that the Sun could be shrinking in size, staying hot and bright as a result.

how do we estimate the masses of binary stars?

Kepler found that the time a planet takes to go around the Sun is related by a specific mathematical formula to its distance from the Sun. In our binary star situation, if two objects are in mutual revolution, then the period (P) with which they go around each other is related to the semimajor axis (D) of the orbit of one with respect to the other, according to this equation

The selection effects (or biases) in the Kepler data are similar to those in Doppler observations.

Large planets are easier to find than small ones, and short-period planets are easier than long-period planets. If we require three transits to establish the presence of a planet, we are of course limited to discovering planets with orbital periods less than one-third of the observing interval. Thus, it was only in its fourth and final year of operation that Kepler was able to find planets with orbits like Earth's that require 1 year to go around their star.

how does a spectrometer work?

Light from the source (actually, the image of a source produced by the telescope) enters the instrument through a small hole or narrow slit, and is collimated (made into a beam of parallel rays) by a lens. The light then passes through a prism, producing a spectrum: different wavelengths leave the prism in different directions because each wavelength is bent by a different amount when it enters and leaves the prism. A second lens placed behind the prism focuses the many different images of the slit or entrance hole onto a CCD or other detecting device. This collection of images (spread out by color) is the spectrum that astronomers can then analyze at a later point. As spectroscopy spreads the light out into more and more collecting bins, fewer photons go into each bin, so either a larger telescope is needed or the integration time must be greatly increased—usually both.

describe the spectra of class T brown dwarfs

Lines of steam (hot water vapor) are present, along with lines of carbon monoxide and neutral sodium, potassium, cesium, and rubidium. Methane (CH4) lines are strong in class-T brown dwarfs, as methane exists in the atmosphere of the giant planets in our own solar system.

What is mass?

Mass which is a measure of the amount of material within an object

what is the problem with the rutherford model?

Maxwell's theory of electromagnetic radiation says that when electrons change either speed or the direction of motion, they must emit energy. Orbiting electrons constantly change their direction of motion, so they should emit a constant stream of energy.-Applying Maxwell's theory to Rutherford's model, all electrons should spiral into the nucleus of the atom as they lose energy, and this collapse should happen very quickly—in about 10-16 seconds.

what is the magnitude scale?

Measurements showed that we receive about 100 times more light from a first-magnitude star than from a sixth-magnitude star. Based on this measurement, astronomers then defined an accurate magnitude system in which a difference of five magnitudes corresponds exactly to a brightness ratio of 100:1.it has a magnitude of 2.0 (or 2.1, 2.3, and so forth). So what number is it that, when multiplied together five times, gives you this factor of 100? Play on your calculator and see if you can get it. The answer turns out to be about 2.5, which is the fifth root of 100. This means that a magnitude 1.0 star and a magnitude 2.0 star differ in brightness by a factor of about 2.5. Likewise, we receive about 2.5 times as much light from a magnitude 2.0 star as from a magnitude 3.0 star. What about the difference between a magnitude 1.0 star and a magnitude 3.0 star? Since the difference is 2.5 times for each "step" of magnitude, the total difference in brightness is 2.5 × 2.5 = 6.25 times.

What is the eccentricity and orbital period of Mercury compared to the other planets?

Mercury has the shortest orbital period and the highest orbital speedAll planets have orbits of rather low eccentricity --> most eccentric orbit, Mars has a eccentricity greater than that of many other planets--> Kepler ellipse deductionAll major planets lie within 10 degrees of the common plane of the solar system

how do the masses and radii of the white dwarfs relate?

Models of white-dwarf structure predict that as the mass of the star increases (toward the right), its radius gets smaller and smaller.

where is the most of neutral hydrogen in the galaxy located?

Modern radio observations show that most of the neutral hydrogen in our Galaxy is confined to an extremely flat layer, less than 300 light-years thick, that extends throughout the disk of the Milky Way Galaxy. This gas has densities ranging from about 0.1 to about 100 atoms per cm3, and it exists at a wide range of temperatures, from as low as about 100 K (-173 °C) to as high as about 8000 K. These regions of warm and cold gas are interspersed with each other, and the density and temperature at any particular point in space are constantly changing.

what is newton's second law & interpretation of the law?

Momentum = Mass X velocityFriction can slow things down and act as an opposing force--> momentum of body can change all the under the action of an outside influenceNewton's second law expresses force in terms of its ability to change momentum with timeA force has both size and direction so that means a force is required to change either the speed or direction of a bodyAcceleration: rate of change in an object's velocityProportional to the force being applied to itGreater the force greater the accelerationThose with less mass will accelerate more if you apply the same amount of force

What are RR Lyrae stars?

More common than the cepheids, but less luminous, thousands of these pulsating variables are known in our Galaxy. The periods of RR Lyrae stars are always less than 1 day, and their changes in brightness are typically less than about a factor of two.

distinguishing true stars and brown dwarfs?

Most brown dwarfs start out with atmospheric temperatures and spectra like those of true stars with spectral classes of M6.5 and later, even though the brown dwarfs are not hot and dense enough in their interiors to fuse hydrogen. In fact, the spectra of brown dwarfs and true stars are so similar from spectral types late M through L that it is not possible to distinguish the two types of objects based on spectra alone

Why is a tremendous amount of energy required to launch an object into space?

Most satellites are launched into low Earth orbit, since this requires the minimum launch energy. At the orbital speed of 8 kilometers per second, they circle the planet in about 90 minuteSome of the very low Earth orbits are not indefinitely stable because, as Earth's atmosphere swells from time to time, a frictional drag is generated by the atmosphere on these satellites, eventually leading to a loss of energy and "decay" of the orbit Artificial and natural satellite act the same = if high enough to be free from atmospheric friction it will remain in orbit forever---> lot of energy to get off Earth

what are variable stars?

Most stars are constant in their luminosity, at least to within a percent or two. Like the Sun, they generate a steady flow of energy from their interiorsHowever, some stars are seen to vary in brightness and, for this reason, are called variable stars. Many such stars vary on a regular cycle, like the flashing bulbs that decorate stores and homes during the winter holidays.

What is an annular eclipse?

Much of the time, the Moon looks slightly smaller than the Sun and cannot cover it completely, even if the two are perfectly aligned. In this type of "annular eclipse," there is a ring of light around the dark sphere of the Moon.

how does dust interact with color?

Much of the violet, blue, and green light from these stars has been scattered or absorbed by dust, so it does not reach Earth. Some of their orange and red light, with longer wavelengths, on the other hand, more easily penetrates the intervening dust and completes its long journey through space to enter Earth-based telescopes (Figure 20.15). Thus, the star looks redder from Earth than it would if you could see it from nearby. (Strictly speaking, reddening is not the most accurate term for this process, since no red color is added; instead, blues and related colors are subtracted, so it should more properly be called "deblueing.") In the most extreme cases, stars can be so reddened that they are entirely undetectable at visible wavelengths and can be seen only at infrared or longer wavelengths

what happens to novae?

Novae fade away in a few months to a few years.Hundreds of novae have been observed, each occurring in a binary star system and each later showing a shell of expelled material. A number of stars have more than one nova episode, as more material from its neighboringstar accumulates on the white dwarf and the whole process repeats. As long as the episodes do not increase the mass of the white dwarf beyond the Chandrasekhar limit (by transferring too much mass too quickly), the dense white dwarf itself remains pretty much unaffected by the explosions on its surface.

what are the seven spectral classes ?

O, B, A, F, G, K, and M. Recently, astronomers have added three additional classes for even cooler objects—L, T, and Y.*** ORDER OF DECREASING TEMP

what about the atomic nuclei of a dying star?

Of course, the dying star also has atomic nuclei in it, not just electrons, but it turns out that the nuclei must be squeezed to much higher densities before their quantum nature becomes apparent. As a result, in white dwarfs, the nuclei do not exhibit degeneracy pressure. Hence, in the white dwarf stage of stellar evolution, it is the degeneracy pressure of the electrons, and not of the nuclei, that halts the collapse of the core.

Explain the Sun illumination/position on the winter solstice in the Northern Hemisphere (what about South hemisphere).

On June 21st all places within 23 degree of the South Pole- south of Antarctic Circle- no sun for 24h Reversed 6 months later, about December 21 (winter solstice)--> Arctic Circle that has 24 hour night and Antarctic Circle that has the midnight Sun. At latitude 23° S, called the Tropic of Capricorn, the Sun passes through the zenith at noon. Days are longer in the Southern Hemisphere and shorter in the north. In the United States and Southern Europe, there may be only 9 or 10 hours of sunshine during the day. It is winter in the Northern Hemisphere and summer in the Southern Hemisphere (44 degrees) Less tilt MIDLER SEASONAL CHANGES--> LOOK AT EXAMPLE 4.1

what is the pledeis cluster?

One of the best-known examples is the nebulosity around each of the brightest stars in the Pleiades cluster (see Figure 20.1). The dust grains are small, and such small particles turn out to scatter light with blue wavelengths more efficiently than light at red wavelengths. A reflection nebula, therefore, usually appears bluer than its illuminating starreflection nebula shines only because the dust within it scatters light from a nearby bright source. The Pleiades cluster is currently passing through an interstellar cloud that contains dust grains, which scatter the light from the hot blue stars in the cluster. The Pleiades cluster is about 400 light-years from the Sun

what if its a two neutron star binary?

One such system has the stars in very close orbits to one another, so much that they continually alter each other's orbit. Another binary neutron star system includes two pulsars that are orbiting each other every 2 hours and 25 minutes. As we discussed earlier, pulsars radiate away their energy, and these two pulsars are slowly moving toward one another, such that in about 85 million years, they will actually merge (see Gravitational Wave Astronomy for our first observations of such a merger).

what are the two ways to detect orbital motion?

One way would be to look for changes in the Sun's position on the sky. The second would be to use the Doppler effect to look for changes in its velocity. Let's discuss each of these in turn.The diameter of Jupiter's apparent orbit viewed from Alpha Centauri is 10 seconds of arc, and that of the Sun's orbit is 0.010 seconds of arc. (Remember, 1 second of arc is 1/3600 degree.) If they could measure the apparent position of the Sun (which is bright and easy to detect) to sufficient precision, they would describe an orbit of diameter 0.010 seconds of arc with a period equal to that of Jupiter, which is 12 years., if they watched the Sun for 12 years, they would see it wiggle back and forth in the sky by this minuscule fraction of a degree. From the observed motion and the period of the "wiggle," they could deduce the mass of Jupiter and its distance using Kepler's laws.

Why is spectral analysis important?

Only in this way can we "sample" the stars, which are too far away for us to visit. Encoded in the electromagnetic radiation from celestial objects is clear information about the chemical makeup of these objects. Only by understanding what the stars were made of could astronomers begin to form theories about what made them shine and how they evolved.

Differences between Palomar telescope and the modern Gemini North telescope

Palomar—>is massive steel structure designed to hold 14.5 tons primary mirror with a 5 meter diameter. Glass tends to sag under its own weight; hence a huge steel structure is needed to hold the mirrorGemini north—> 8 meters in diameter, if it were built using same tech as Palomar telescope, would have to weigh at least 8 times S much and would require an enormous steel structure to support it Gemini North mirror is only about 8 inches thick and weighs 24.5 tons, less than twice as much as the Palomar mirror. The Gemini North telescope was completed about 50 years after the Palomar telescopeuse active control to correct sag

What is perihelion? Aphelion?

Perihelion is when the Earth is closest to the sun and moving the fast, while Aphelion is the furthest away and moves the slowest (perigee and apogee for the moon)

what are the limitations of photography?

Photographic films are inefficient: only about 1% of the light that actually falls on the film contributes to the chemical change that makes the image; the rest is wasted.

What is the zenith?

Point directly above the observer

How do we use quasars to detect the Big Bang?

Quasars allow us to see Big Bang explosion that marks the beginning of timedetected the feeble glow of the explosion itself, filling the universe and thus coming to us from all directions in space.

the period luminosity variables in Cepheid variables?

RR lyrae stars bottom leftcepheids the rest

how are cosmic radio waves measured?

Radio waves can produce a current in conductors of electricity such as metals. An antenna is such a conductor: it intercepts radio waves, which create a feeble current in it. The current is then amplified in a radio receiver until it is strong enough to measure or record.astronomers use sophisticated data-processing techniques that allow thousands of separate frequency bands to be detected simultaneously.

how do we find the nearby stars we can't see by naked eye?

Recent discoveries of nearby stars have relied heavily upon infrared telescopes that are able to find these many cool, low-mass stars.

why the higher the temp the shorter the wavelength at which maximum power is emitted?

Remember that a shorter wavelength means a higher frequency and energy. It makes sense, then, that hot objects give off a larger fraction of their energy at shorter wavelengths (higher energies) than do cool objects.You may have observed examples of this rule in everyday life. When a burner on an electric stove is turned on low, it emits only heat, which is infrared radiation, but does not glow with visible light. If the burner is set to a higher temperature, it starts to glow a dull red.

What does theory predict for the H-R diagram of a cluster whose stars have recently condensed from an interstellar cloud?

Remember that at every stage of evolution, massive stars evolve more quickly than their lower-mass counterparts. After a few million years ("recently" for astronomers), the most massive stars should have completed their contraction phase and be on the main sequence, while the less massive ones should be off to the right, still on their way to the main sequence.illustrated by HR diagram

why is the sun not cooling down?

Scientists conclude that the temperature is highest at the center of a star, dropping to lower and lower values toward the stellar surface. (The high temperature of the Sun's chromosphere and corona may therefore appear to be a paradox. But remember from The Sun: A Garden-Variety Star that these high temperatures are maintained by magnetic effects, which occur in the Sun's atmosphere.)The outward flow of energy through a star robs it of its internal heat, and the star would cool down if that energy were not replaced. Similarly, a hot iron begins to cool as soon as it is unplugged from its source of electric energy. Therefore, a source of fresh energy must exist within each star. In the Sun's case, we have seen that this energy source is the ongoing fusion of hydrogen to form helium.

what is a model star?

Scientists use the principles we have just described to calculate what the Sun's interior is like. These physical ideas are expressed as mathematical equations that are solved to determine the values of temperature, pressure, density, the efficiency with which photons are absorbed, and other physical quantities throughout the Sun. The solutions obtained, based on a specific set of physical assumptions, provide a theoretical model for the interior of the Sun.

parallax diagram?

Seen from opposite sides of Earth's orbit, a nearby star shifts position when compared to a pattern of more distant stars. Astronomers actually define parallax to be one-half the angle that a star shifts when seen from opposite sides of Earth's orbit (the angle labeled P in Figure 19.6). The reason for this definition is just that they prefer to deal with a baseline of 1 AU instead of 2 AU.As Earth revolves around the Sun, the direction in which we see a nearby star varies with respect to distant stars. We define the parallax of the nearby star to be one half of the total change in direction, and we usually measure it in arcsecond

2 step in fusion in sun : what happens to the positron formed in step one?

Since it is antimatter, this positron will instantly collide with a nearby electron, and both will be annihilated, producing electromagnetic energy in the form of gamma-ray photons.This gamma ray, which has been created in the center of the Sun, finds itself in a world crammed full of fast-moving nuclei and electrons. The gamma ray collides with particles of matter and transfers its energy to one of them. The particle later emits another gamma-ray photon, but often the emitted photon has a bit less energy than the one that was absorbedSuch interactions happen to gamma rays again and again and again as they make their way slowly toward the outer layers of the Sun, until their energy becomes so reduced that they are no longer gamma rays but X- raysLater, as the photons lose still more energy through collisions in the crowded center of the Sun, they become ultraviolet photons.

whats the difference between nuclear attraction & electric repulsion?

Since like charges repel via the electrical force (postive charges from the two nuclei we are trying tojoin) , the closer we get two nuclei to each other, the more they repel.get them within "striking distance" (which is very tiny about the size of a nucleus) of the nuclear force, they will then come together with a much stronger attraction.

what are fusion stars?

Since only 0.7% of the hydrogen used in fusion reactions is converted into energy, fusion does not change the total mass of the star appreciably during this long period. It does, however, change the chemical composition in its central regions where nuclear reactions occur: hydrogen is gradually depleted, and helium accumulates. This change of composition changes the luminosity, temperature, size, and interior structure of the star. When a star's luminosity and temperature begin to change, the point that represents the star on the H-R diagram moves away from the zero-age main sequence.

what is a reflection nebula?

Some dense clouds of dust are close to luminous stars and scatter enough starlight to become visible. Such a cloud of dust, illuminated by starlight, is called a reflection nebula, since the light we see is starlight reflected off the grains of dust.

what kind of stars are within 21 light years of the Sun?

Spectral Type. #of StarsA 2F 1G 7K 17M 94White Dwarfs. 8Brown Dwarfs. 33 Only three of the stars in our local neighborhood (one F type and two A types) are significantly more luminous and more massive than the Sun

how do main sequence stars maintain there equilibrium? will they run out of fuel ?d

Stable (main-sequence) stars such as our Sun maintain equilibrium by producing energy through nuclear fusion in their cores. The ability to generate energy by fusion defines a star.Each second in the Sun, approximately 600 million tons of hydrogen undergo fusion into helium, with about 4 million tons turning into energy in the process. This rate of hydrogen use means that eventually the Sun (and all other stars) will run out of central fuel.

how does star formation propagate?

Star formation can move progressively through a molecular cloud. The oldest group of stars lies to the left of the diagram and has expanded because of the motions of individual stars. Eventually, the stars in the group will disperse and no longer be recognizable as a cluster. The youngest group of stars lies to the right, next to the molecular cloud. This group of stars is only 1 to 2 million years old. The pressure of the hot, ionized gas surrounding these stars compresses the material in the nearby edge of the molecular cloud and initiates the gravitational collapse that will lead to the formation of more stars.

describe the masses of the stars?

Stars come with many different masses, ranging from 1/12 solar masses (MSun) to roughly 100-200 MSun. There are far more low-mass than high-mass stars.The most massive main-sequence stars (spectral type O) are also the most luminous and have the highest surface temperature. The lowest-mass stars on the main sequence (spectral type M or L) are the least luminous and the coolest.A galaxy of stars such as the Milky Way contains enormous amounts of gas and dust—enough to make billions of stars like the Sun.

how large can stars be?

Stars more massive than the Sun are rare. None of the stars within 30 light-years of the Sun has a mass greater than four times that of the Sun. Searches at large distances from the Sun have led to the discovery of a few stars with masses up to about 100 times that of the Sun, and a handful of stars (a few out of several billion) may have masses as large as 250 solar masses. However, most stars have less mass than the Sun.

What were early calendars?

Stonehedge: tones are aligned with the directions of the Sun and Moon during their risings and settings at critical times of the year (such as the summer and winter solstices), and it is generally believed that at least one function of the monument was connected with the keeping of a calendar.Mayan Calendar: did not attempt to correlate their calendar accurately with the length of the year or lunar month. Rather, their calendar was a system for keeping track of the passage of days and for counting time far into the past or future. Among other purposes, it was useful for predicting astronomical events, such as the position of Venus in the skyAncient Chinese: In addition to the motions of Earth and the Moon, they were able to fit in the approximately 12-year cycle of Jupiter, which was central to their system of astrology. The Chinese still preserve some aspects of this system in their cycle of 12 "years"—the Year of the Dragon, the Year of the Pig, and so on—that are defined by the position of Jupiter in the zodiac.Western Calendars: --> Sumerians --> Egyptians and Greeks --> Julian Calendar-->which approximated the year at 365.25 days, fairly close to the actual value of 365.2422. The Romans achieved this approximation by declaring years to have 365 days each, with the exception of every fourth year. The leap year was to have one extra day, bringing its length to 366 days, and thus making the average length of the year in the Julian calendar 365.25 days --> dropped trying to base calendars off of moon and sun

is the destruction of a white dwarf star binary system a supernova?

Such an explosion is also called a supernova, since, like the destruction of a high-mass star, it produces a huge amount of energy in a very short time. However, unlike the explosion of a high-mass star, which can leave behind a neutron star or black hole remnant, the white dwarf is completely destroyed in the process, leaving behind no remnant. We call these white dwarf explosions type Ia supernovae

how do we measure characteristics of stars?

Surface temperature1. Determine the color (very rough).2. Measure the spectrum and get the spectral type.Chemical compositionDetermine which lines are present in the spectrum.LuminosityMeasure the apparent brightness and compensate for distance.Radial VelocityMeasure the Doppler shift in the spectrum.MassMeasure the period and radial velocity curves of spectroscopic binary stars.RotationMeasure the width of spectral lines.Diameter1. Measure the way a star's light is blocked by the Moon.2. Measure the light curves and Doppler shifts for eclipsing binary stars.

What are neap tides?

Sun partially cancel the tides of the Moon, making them lower than usual. These are called neap tides

explain the lunar cycle

Sun moves 1/12 its path around the sky each month, but we can assume the Sun' light is constant through a moon's four week cycleMove moves completely around earth in that timehow much of moon face we see illuminated depends on the angle the sun makes with the MoonThe moon = new when it is in the same general direction in the sky as the Sun ( A)--> moon invisible to us because new mon is the same part of the sky as the sun, it rises at sunrise & sets at sunsetMoves 12 degrees in the sky each day (24 times its own diameter)A day or two later = thin crescent first appears, as we begin to see a small part of the Moon's illuminated hemisphere--> reflects a little sunlight towards us along one sides--> increases in size on successive days as Moon moves farther & farther around the sky away from Sun (B)--> moon is moving eastward away from the Sun, it rises later & later each daythe Moon is one-quarter of the way around its orbit (position C) and so we say it is at the first quarter phase. Half of the Moon's illuminated side is visible to Earth observers. Because of its eastward motion, the Moon now lags about one-quarter of the day behind the Sun, rising around noon and setting around midnightDuring the week after the first quarter phase, we see more and more of the Moon's illuminated hemisphere (position D), a phase that is called waxing (or growing) gibbous.Eventually, the Moon arrives at position E in our figure, where it and the Sun are opposite each other in the sky--> full moonMoon rises at sunset and setting at sunriseHighest and most noticeable in midnightMore likely to notice or remember b/c of bright celestial lightDuring the two weeks following the full moon, the Moon goes through the same phases again in reverse order returning to new phase after about 29.5 days. About a week after the full moon, for example, the Moon is at third quarter, meaning that it is three-quarters of the way around (not that it is three-quarters illuminated—in fact, half of the visible side of the Moon is again dark). At this phase, the Moon is now rising around midnight and setting around noon.And, since the Moon's orbit is tilted relative to the path of the Sun in the sky, Earth's shadow misses the Moon most months. That's why we regularly get treated to a full moon.The times when Earth's shadow does fall on the Moon are called lunar eclipses

How the bohr model explains why atoms absorb or emit only specific energies or wavelengths of light?

Suppose a beam of white light (which consists of photons of all visible wavelengths) shines through a gas of atomic hydrogen. A photon of wavelength 656 nanometers has just the right energy to raise an electron in a hydrogen atom from the second to the third orbit. Thus, as all the photons of different energies (or wavelengths or colors) stream by the hydrogen atoms, photons with this particular wavelength can be absorbed by those atoms whose electrons are orbiting on the second level. When they are absorbed, the electrons on the second level will move to the third level, and a number of the photons of this wavelength and energy will be missing from the general stream of white light.only photons with these exact energies can be absorbed. All of the other photons will stream past the atoms untouched. Thus, hydrogen atoms absorb light at only certain wavelengths and produce dark lines at those wavelengths in the spectrum we see.

what are interstellar grain?

Thanks to their small sizes and low temperatures, interstellar grains radiate most of their energy at infrared to microwave frequencies, with wavelengths of tens to hundreds of microns. Earth's atmosphere is opaque to radiation at these wavelengths, so emission by interstellar dust is best measured from space. Observations from above Earth's atmosphere show that dust clouds are present throughout the plane of the Milky Way

why are white dwarf explosions called Ia supernovae?

The "a" subdesignation of type Ia supernovae further refers to the presence of strong silicon absorption lines, which are absent from supernovae originating from the collapse of massive stars. Silicon is one of the products that results from the fusion of carbon and oxygen, which bears out the scenario we described above—that there is a sudden onset of the fusion of the carbon (and oxygen) of which the white dwarf was made.

how do we use baseline surveyors and the moon?

The Moon is the only object near enough that its distance can be found fairly accurately with measurements made without a telescope. Ptolemy determined the distance to the Moon correctly to within a few percent. He used the turning Earth itself as a baseline, measuring the position of the Moon relative to the stars at two different times of night.

is the sun reddening?

The Sun appears much redder at sunset than it does at noon. The lower the Sun is in the sky, the longer the path its light must travel through the atmosphere. Over this greater distance, there is a greater chance that sunlight will be scattered. Since red light is less likely to be scattered than blue light, the Sun appears more and more red as it approaches the horizon.

what is a plasma?

The Sun is so hot that all of the material in it is in the form of ionized gas, called a plasma. Plasma acts much like a hot gas, which is easier to describe mathematically than either liquids or solids. The particles that constitute a gas are in rapid motion, frequently colliding with one another. This constant bombardment is the pressure of the gasMore particles within a given volume of gas produce more pressure because the combined impact of the moving particles increases with their number. The pressure is also greater when the molecules or atoms are moving faster. Since the molecules move faster when the temperature is hotter, higher temperatures produce higher pressure.

With a baseline of one AU, how far away would a star have to be to have a parallax of 1 arcsecond?

The answer turns out to be 206,265 AU, or 3.26 light-years. This is equal to 3.1 × 1013 kilometers (in other words, 31 trillion kilometers).

What is right ascension?

The arbitrarily chosen point where we start counting is the vernal equinox (a point in the sky where the ecliptic (the sun's path) crosses the celestial equator) Can be expression as units of angle (degrees) or units of time--> b/c celestial sphere appears to turn around Earth once a day as our planet turns on its axisThus the 360° of RA that it takes to go once around the celestial sphere can just as well be set equal to 24 hours. Then each 15° of arc is equal to 1 hour of time

ionization energy

The atom is then said to be ionized. The minimum amount of energy required to remove one electron from an atom in its ground state

what is direct imaging in characterizing exoplanets?

The brightness of the planet can be measured at different wavelengths. These observations provide an estimate for the temperature of the planet's atmosphere; in the case of HR 8799 planet 1, the color suggests the presence of thick clouds. Spectra can also be obtained from the faint light to analyze the atmospheric constituents. A spectrum of HR 8799 planet 1 indicates a hydrogen-rich atmosphere, while the closer planet 4 shows evidence for methane in the atmosphere.

Eventually, all the hydrogen in a star's core, where it is hot enough for fusion reactions, is used up. What happens ?

The core then contains only helium, "contaminated" by whatever small percentage of heavier elements the star had to begin with. The helium in the core can be thought of as the accumulated "ash" from the nuclear "burning" of hydrogen during the main-sequence stage.Energy can no longer be generated by hydrogen fusion in the stellar core because the hydrogen is all gone and, as we will see, the fusion of helium requires much higher temperatures. Since the central temperature is not yet high enough to fuse helium, there is no nuclear energy source to supply heat to the central region of the star. The long period of stability now ends, gravity again takes over, and the core begins to contract. Once more, the star's energy is partially supplied by gravitational energy, in the way described by Kelvin and Helmholtz. As the star's core shrinks, the energy of the inward- falling material is converted to heat.

how do the degenerate electrons act?

The degenerate electrons do not require an input of heat to maintain the pressure they exert, and so a star with this kind of structure, if nothing disturbs it, can last essentially forever. (Note that the repulsive force between degenerate electrons is different from, and much stronger than, the normal electrical repulsion between charges that have the same sign.)The electrons in a degenerate gas do move about, as do particles in any gas, but not with a lot of freedom. A particular electron cannot change position or momentum until another electron in an adjacent stage gets out of the way. The situation is much like that in the parking lot after a big football game. Vehicles are closely packed, and a given car cannot move until the one in front of it moves, leaving an empty space to be filled.

why does the core only shrink a little bit at the beginning?

The electrons at first resist being crowded closer together, and so the core shrinks only a small amount. Ultimately, however, the iron core reaches a mass so large that even degenerate electrons can no longer support it. When the density reaches 4 × 1011 g/cm3 (400 billion times the density of water), some electrons are actually squeezed into the atomic nuclei, where they combine with protons to form neutrons and neutrinos. This transformation is not something that is familiar from everyday life, but becomes very important as such a massive star core collapses.Some of the electrons are now gone, so the core can no longer resist the crushing mass of the star's overlying layers. The core begins to shrink rapidly. More and more electrons are now pushed into the atomic nuclei, which ultimately become so saturated with neutrons that they cannot hold onto them.

what is degenerate gas?

The electrons in a degenerate gas resist further crowding with tremendous pressure. (It's as if the electrons said, "You can press inward all you want, but there is simply no room for any other electrons to squeeze in here without violating the rules of our existence.")

what is the problem with eyes as detectors?

The eye also suffers from having a very short integration time; it takes only a fraction of a second to add light energy together before sending the image to the brain. One important advantage of modern detectors is that the light from astronomical objects can be collected by the detector over longer periods of time; this technique is called "taking a long exposure." Exposures of several hours are required to detect very faint objects in the cosmos.

what are baseline surveyors?

The farther away an astronomical object lies, the longer the baseline has to be to give us a reasonable chance of making a measurement. Unfortunately, nearly all astronomical objects are very far away. To measure their distances requires a very large baseline and highly precise angular measurements.

what is the first white dwarf?

The first white dwarf star was detected in 1862. Called Sirius B, it forms a binary system with Sirius A, the brightest-appearing star in the sky. It eluded discovery and analysis for a long time because its faint light tends to be lost in the glare of nearby Sirius A

how is the structure of molecular clouds maintained?

The force of gravity, pulling inward, tries to make a star collapse. Internal pressure produced by the motions of the gas atoms, pushing outward, tries to force the star to expand. When a star is first forming, low temperature (and hence, low pressure) and high density (hence, greater gravitational attraction) both work to give gravity the advantage. In order to form a star—that is, a dense, hot ball of matter capable of starting nuclear reactions deep within—we need a typical core of interstellar atoms and molecules to shrink in radius and increase in density by a factor of nearly 1020. It is the force of gravity that produces this drastic collapse.

what is metallicity?

The fraction of a star's mass that is composed of these elements is referred to as the star's metallicity. The metallicity of the Sun, for example, is 0.02, since 2% of the Sun's mass is made of elements heavier than helium.

what is the limit to which building up elements by fusion can go on.?

The fusion of silicon into iron turns out to be the last step in the sequence of nonexplosive element production. Up to this point, each fusion reaction has produced energy because the nucleus of each fusion product has been a bit more stable than the nuclei that formed it.light nuclei give up some of their binding energy in the process of fusing into more tightly bound, heavier nuclei. It is this released energy that maintains the outward pressure in the core so that the star does not collapse. But of all the nuclei known, iron is the most tightly bound and thus the most stable.

what is the relationship between radiation and temperature?

The hotter the solid or gas, the more rapid the motion of its molecules or atoms. The temperature of something is thus a measure of the average motion energy of the particles that make it up.

What is the zero age main sequence?

The left-hand edge of the main-sequence band in the H-R diagramWe use the term zero-age to mark the time when a star stops contracting, settles onto the main sequence, and begins to fuse hydrogen in its core. The zero-age main sequence is a continuous line in the H-R diagram that shows where stars of different masses but similar chemical composition can be found when they begin to fuse hydrogen

What causes the twinkling of stars?

The light beams are bent enough that part of the time they reach your eye, and part of the time some of them miss, thereby making the star seem to vary in brightness. In space, however, the light of the stars is steady.

how does the doppler effect pulsating variable stars?

The lines in the spectrum shift toward the blue as the surface of the star moves toward us and then shift to the red as the surface shrinks back. As the star pulsates, it also changes its overall color, indicating that its temperature is also varying. And, most important for our purposes, the luminosity of the pulsating variable also changes in a regular way as it expands and contracts.

what is the main sequence turnoff?

The location in the H-R diagram where the stars have begun to leave the main sequence

what are spectroscopic parallax?

The method of determining a star's distance by comparing its apparent magnitude with its absolute magnitude, as estimated from its spectrum.The H-R diagram method allows astronomers to estimate distances to nearby stars, as well as some of the most distant stars in our Galaxy, but it is anchored by measurements of parallax. The distances measured using parallax are the gold standard for distances: they rely on no assumptions, only geometry. Once astronomers take a spectrum of a nearby star for which we also know the parallax, we know the luminosity that corresponds to that spectral type. Nearby stars thus serve as benchmarks for more distant stars because we can assume that two stars with identical spectra have the same intrinsic luminosity

What is a concave primary mirror?

The mirror is curved like the inner surface of a sphere, and it reflects light in order to form an image coated with a shiny metal, usually silver, aluminum, or, occasionally, gold, to make them highly reflective. If the mirror has the correct shape, all parallel rays are reflected back to the same point, the focus of the mirror. Thus, images are produced by a mirror exactly as they are by a lens.

mass & temp relationship on H-R diagram?

The model stars with the largest masses are the hottest and most luminous, and they are located at the upper left of the diagram.The least-massive model stars are the coolest and least luminous, and they are placed at the lower right of the plot. The other model stars all lie along a line running diagonally across the diagram. In other words, the main sequence turns out to be a sequence of stellar masses.

the describe evolution of a binary star?

The more massive star evolves first to become a red giant and then a white dwarf. The white dwarf then begins to attract material from its companion, which in turn evolves to become a red giant. Eventually, the white dwarf acquires so much mass that it is pushed over the Chandrasekhar limit and becomes a type Ia supernova.

how much more luminous than the sun the most luminous of bright stars?

The most luminous of the bright stars listed in Appendix J emit more than 50,000 times more energy than does the Sun. These highly luminous stars are missing from the solar neighborhood because they are very rare. None of them happens to be in the tiny volume of space immediately surrounding the Sun, and only this small volume was surveyed to get the data shown in Table 18.1.

why does the mass and temp relationship on H-R diagram makes sense?

The most massive stars have the most gravity and can thus compress their centers to the greatest degree. This means they are the hottest inside and the best at generating energy from nuclear reactions deep within. As a result, they shine with the greatest luminosity and have the hottest surface temperatures. The stars with lowest mass, in turn, are the coolest inside and least effective in generating energy. Thus, they are the least luminous and wind up being the coolest on the surface. Our Sun lies somewhere in the middle of these extremes (as you can see in Figure 18.14). The characteristics of representative main-sequence stars (excluding brown dwarfs, which are not true stars) are listed in Table 18.3.

what are the air limitations on usefulness of telescopes?

The most obvious limitation is weather conditions such as clouds, wind, and rain. At the best sites, the weather is clear as much as 75% of the time.Even on a clear night, the atmosphere filters out a certain amount of starlight, especially in the infrared, where the absorption is due primarily to water vapor. Astronomers therefore prefer dry sites, generally found at high altitudes.The sky above the telescope should be dark. Near cities, the air scatters the glare from lights, producing an illumination that hides the faintest stars and limits the distances that can be probed by telescopes. (Astronomers call this effect light pollution.) Observatories are best located at least 100 miles from the nearest large city.Finally, the air is often unsteady; light passing through this turbulent air is disturbed, resulting in blurred star images. Astronomers call these effects "bad seeing." When seeing is bad, images of celestial objects are distorted by the constant twisting and bending of light rays by turbulent air.

What is an orbit?

The path of any object under the influence of gravity through space

What is totality?

The path where the shadow falls directly on Earth (solar) or the moon (lunar).

What is photometry?

The process of measuring the apparent brightness of stars is called photometry

what are the ionizations of collisions?

The rate at which such collisional ionizations occur depends on the speeds of the atoms and hence on the temperature of the gas—the hotter the gas, the more of its atoms will be ionized.

what causes the red glow of the Orion Nebula?

The red glow that pervades the great Orion Nebula is produced by the first line in the Balmer series of hydrogen. Hydrogen emission indicates that there are hot young stars nearby that ionize these clouds of gas. When electrons then recombine with protons and move back down into lower energy orbits, emission lines are produced. The blue color seen at the edges of some of the clouds is produced by small particles of dust that scatter the light from the hot stars. Dust can also be seen silhouetted against the glowing gas.

what is the second step of fusion in sun?

The second step in forming helium from hydrogen is to add another proton to the deuterium nucleus to createa helium nucleus that contains two protons and one neutron (Figure 16.7). In the process, some mass is again lost and more gamma radiation is emitted. Such a nucleus is helium because an element is defined by its number of protons; any nucleus with two protons is called helium. But this form of helium, which we call helium-3 (and write in shorthand as 3He) is not the isotope we see in the Sun's atmosphere or on Earth. That helium has two neutrons and two protons and hence is called helium-4 (4He).To get to helium-4 in the Sun, helium-3 must combine with another helium-3 in the third step of fusion (illustrated in Figure 16.8). Note that two energetic protons are left over from this step; each of them comes out of the reaction ready to collide with other protons and to start step 1 in the chain of reactions all over again.

what is the cosmic distance ladder?

The succession of methods by which astronomers determine the distances to celestial objects.Parallaxes are the foundation of all stellar distance estimates, spectroscopic methods use nearby stars to calibrate their H-R diagrams, and RR Lyrae and cepheid distance estimates are grounded in H-R diagram distance estimates (and even in a parallax measurement to a nearby cepheid, Delta Cephei).This chain of methods allows astronomers to push the limits when looking for even more distant stars. Recent work, for example, has used RR Lyrae stars to identify dim companion galaxies to our own Milky Way out at distances of 300,000 light-years. The H-R diagram method was recently used to identify the two most distant stars in the Galaxy: red giant stars way out in the halo of the Milky Way with distances of almost 1 million light- years

how do we figure out diameters of eclipsing binary stars?

The technique involves making a light curve of an eclipsing binary, a graph that plots how the brightness changes with time.Even though we cannot see the two stars separately in such a system, the light curve can tell us what is happening. When the smaller star just starts to pass behind the larger star (a point we call first contact), the brightness begins to drop. The eclipse becomes total (the smaller star is completely hidden) at the point called second contact. At the end of the total eclipse (third contact), the smaller star begins to emerge. When the smaller star has reached last contact, the eclipse is completely over

what does the electrons in a star typically do for most of a stars live?

The temperature in the interior of a star is always so high that the atoms are stripped of virtually all their electrons. For most of a star's life, the density of matter is also relatively low, and the electrons in the star are moving rapidly. This means that no two of them will be in the same place moving in exactly the same way at the same time. But this all changes when a star exhausts its store of nuclear energy and begins its final collapse.

But there are stars whose core masses are greater than 3 MSun when they exhaust their fuel supplies. What becomes of them

The truly bizarre result of the death of such massive stellar cores (called a black hole)

what is interstellar extinction?

The tiny interstellar dust grains absorb some of the starlight they intercept. But at least half of the starlight that interacts with a grain is merely scattered, that is, it is redirected rather than absorbed. Since neither the absorbed nor the scattered starlight reaches us directly, both absorption and scattering make stars look dimmer. The effects of both processes are called interstellar extinction

What is an isotope?

The various types of hydrogen nuclei with different numbers of neutrons are called isotopes of hydrogen closely related but with different characteristics and behaviors.

Most of the volume of the interstellar medium is filled with neutral (nonionized) hydrogen. How do we go about looking for it?

The very hot stars required to produce H II regions are rare, and only a small fraction of interstellar matter is close enough to such hot stars to be ionized by them.neutral hydrogen atoms at temperatures typical of the gas in interstellar space neither emit nor absorb light in the visible part of the spectrum. Nor, for the most part, do the other trace elements that are mixed with the interstellar hydrogen. However, some of these other elements can absorb visible light even at typical interstellar temperatures. This means that when we observe a bright source such as a hot star or a galaxy, we can sometimes see additional lines in its spectrum produced when interstellar gas absorbs light at particular frequencies. Some of the strongest interstellar absorption lines are produced by calcium and sodium, but many other elements can be detected as well in sufficiently sensitive observations

What is Wien's Law?

The wavelength at which maximum power is emitted where the wavelength is in nanometers (one billionth of a meter) and the temperature is in K (the constant 3 x 10^6 has units of nm × K).

what are the disks around protostars?

These Hubble Space Telescope infrared images show disks around young stars in the constellation of Taurus, in a region about 450 light-years away. In some cases, we can see the central star (or stars—some are binaries). In other cases, the dark, horizontal bands indicate regions where the dust disk is so thick that even infrared radiation from the star embedded within it cannot make its way through. The brightly glowing regions are starlight reflected from the upper and lower surfaces of the disk, which are less dense than the central, dark regions

what are conditions inside giant molecular clouds?

These clouds have cold interiors with characteristic temperatures of only 10-20 K; most of their gas atoms are bound into molecules. These clouds turn out to be the birthplaces of most stars in our Galaxy.

What are globular clusters?

They are stars in a galaxy that form clusters. Without a telescope, this cluster would seem to be a singular star.

describe the evolutionary track of a star like the sun?

This diagram shows the changes in luminosity and surface temperature for a star with a mass like the Sun's as it nears the end of its life. After the star becomes a giant again (point A on the diagram), it will lose more and more mass as its core begins to collapse. The mass loss will expose the hot inner core, which will appear at the center of a planetary nebula. In this stage, the star moves across the diagram to the left as it becomes hotter and hotter during its collapse (point B). At first, the luminosity remains nearly constant, but as the star begins to cool off, it becomes less and less bright (point C). It is now a white dwarf and will continue to cool slowly for billions of years until all of its remaining store of energy is radiated away. (This assumes the Sun will lose between 46-50% of its mass during the giant stages, based upon various theoretical models).

compare the amount of energy of hot temps and cold temps

This graph shows in arbitrary units how many photons are given off at each wavelength for objects at four different temperatures. The wavelengths corresponding to visible light are shown by the colored bands. Note that at hotter temperatures, more energy (in the form of photons) is emitted at all wavelengths. The higher the temperature, the shorter the wavelength at which the peak amount of energy is radiated (this is known as Wien's law).

Describe the Type Ia supernovae?

This type of supernova is brighter than supernovae produced by the collapse of a massive star. Thus, type Ia supernovae can be seen at very large distances, and they are found in all types of galaxies. The energy output from most type Ia supernovae is consistent, with little variation in their maximum luminosities, or in how their light output initially increases and then slowly decreases over time. These properties make type Ia supernovae extremely valuable "standard bulbs" for astronomers looking out at great distances—well beyond the limits of our own Galaxy.In contrast, type II supernovae are about 5 times less luminous than type Ia supernovae and are only seen in galaxies that have recent, massive star formation. Type II supernovae are also less consistent in their energy output during the explosion and can have a range a peak luminosity values.

what was the first detection of stellar parallax?

Thomas Henderson, a Scottish astronomer working at the Cape of Good Hope, and Friedrich Struve in Russia independently measured the parallaxes of the stars 61 Cygni, Alpha Centauri, and Vega, respectively. Even the closest star, Alpha Centauri, showed a total displacement of only about 1.5 arcseconds during the course of a year

how is an interplanetary aircraft affect by different gravities in space?

To escape earth these crafts must achieve escape speed, the speed needed to move away from earth forever, which is about 11 kilometers per secondIn interplanetary flight, these spacecraft follow orbits around the sun that are modified only when they pass near one of the planetsAs it comes closer to its target a spacecraft is deflected by the planet's gravitational force into a modified orbit either gaining or losing energy in the process--> the gravitational force can be used to redirect a spacecraft was having targetin order to orbit a planet you must slow the spacecraft allowing it to be captured into an elliptical orbit and additional rocket thrust to bring the vehicle down from orbit and onto a surface

But stars do not have the same luminosity so...

To measure the luminosities of stars, we must first compensate for the dimming effects of distance on light, and to do that, we must know how far away they are.Distance is among the most difficult of all astronomical measurements.

what is a blackbody?

To understand, in more quantitative detail, the relationship between temperature and electromagnetic radiation,......... A hypothetical object that absorbs all of the radiation that strikes it. The energy that is absorbed causes the atoms and molecules in it to vibrate or move around at increasing speeds. As it gets hotter, this object will radiate electromagnetic waves until absorption and radiation are in balance. We want to discuss such an idealized object because, as you will see, stars behave in very nearly the same way.

describe how gravity works when two people are falling down a pit and playing catch

Two people play catch as they descend into a bottomless abyss. Since the people and ball all fall at the same speed, it appears to them that they can play catch by throwing the ball in a straight line between them. Within their frame of reference, there appears to be no gravity.

what electromagnetic waves can only be observed from space?

Ultraviolet, X-ray, and direct gamma-ray (high-energy electromagnetic wave) observations can be made only from space.

What is Kepler's third law?

Wanted to know why the orbits of the planets were spaced out as they are and tried to find a mathematical pattern of their movementsOrbital period: the time it takes a planet to travel once around the suntell me major axis= average distance from the sunKepler's third law says that a planet's orbital speed(years) squared is proportional to the semimajor axis(astronomical unit) of its orbit cubed (P^2 ∝ a^3) Earth, and provides a means for calculating their relative distances from the Sun from the time they take to orbit

wavelength and frequency relationship

Waves with longer wavelengths have lower frequencies-->vice versa

how to determine mass of the stars in a spectroscopic binary?

We can analyze a radial velocity curveWe measure the speeds of the stars from the Doppler effect. We then determine the period—how long the stars take to go through an orbital cycle—from the velocity curve. Knowing how fast the stars are moving and how long they take to go around tells us the circumference of the orbit and, hence, the separation of the stars in kilometers or astronomical units. From Kepler's law, the period and the separation allow us to calculate the sum of the stars' masses.

Why can we see other planets in the solar system ( why is harder to view planets further away?)

We can see planets in our solar system because it reflects the light of the planet

What is the difference type 1 and type 2 supernovae?

We distinguish type I supernovae from those of supernovae of type II originating from the death of massive stars discussed earlier by the absence of hydrogen in their observed spectra. Hydrogen is the most common element in the universe and is a major component of massive, evolved stars. However, as we learned earlier, hydrogen is absent from the white dwarf remnant, which is primarily composed of carbon and oxygen for masses comparable to the Chandrasekhar mass limit.

what is the parsec?

We give this unit a special name, the parsec (pc)—derived from "the distance at which we have a parallax of one second." The distance (D) of a star in parsecs is just the reciprocal of its parallax (p) in arcseconds;D = 1/pThus, a star with a parallax of 0.1 arcsecond would be found at a distance of 10 parsecs, and one with a parallaxof 0.05 arcsecond would be 20 parsecs away.1 parsec = 3.26 light-year, and 1 light-year = 0.31 parsec.

why is the sun a representative star?

We saw that what stars such as the Sun "do for a living" is to convert protons into helium deep in their interiors via the process of nuclear fusion, thus producing energy. The fusion of protons to helium is an excellent, long-lasting source of energy for a star because the bulk of every star consists of hydrogen atoms, whose nuclei are protons.

describe the Young Cluster H-R Diagram

We see an H-R diagram for a hypothetical young cluster with an age of 3 million years. Note that the high-mass (high-luminosity) stars have already arrived at the main-sequence stage of their lives, while the lower-mass (lower-luminosity) stars are still contracting toward the zero-age main sequence (the red line) and are not yet hot enough to derive all of their energy from the fusion of hydrogen.There are real star clusters that fit this description. The first to be studied (in about 1950) was NGC 2264, which is still associated with the region of gas and dust from which it was born

describe the doppler shift in stars (what color if approaching vs moving away?)

We should see all the spectral lines of moving stars shifted toward the red end of the spectrum if the star is moving away from us, or toward the blue (violet) end if it is moving toward us (Figure 17.10). The greater the shift, the faster the star is moving.along the line of sight between the star and the observer, is called radial velocity and is usually measured in kilometers per second.

Explain the spiraling of the moon

What Darwin calculated for the Earth-Moon system was that the Moon will slowly spiral outward, away from Earth. As it moves farther away, it will orbit less quickly (just as planets farther from the Sun move more slowly in their orbits). Thus, the month will get longer. Also, because the Moon will be more distant, total eclipses of the Sun will no longer be visible from EarthMoving away at 3.8 cm each year = billions of year day and month will be the same length

What would happen if there were no continuous spectrum for our gases to remove light from?

What if, instead, we heated the same thin gases until they were hot enough to glow with their own light? When the gases were heated, a spectrometer revealed no continuous spectrum, but several separate bright lines. That is, these hot gases emitted light only at certain specific wavelengths or colors.

what happens to radius of white dwarf in its final stages?

When Chandrasekhar made his calculation about white dwarfs, he found something very surprising: the radius of a white dwarf shrinks as the mass in the star increases (the larger the mass, the more tightly packed the electrons can become, resulting in a smaller radius). According to the best theoretical models, a white dwarf with a mass of about 1.4 MSun or larger would have a radius of zero. What the calculations are telling us is that even the force of degenerate electrons cannot stop the collapse of a star with more mass than this

how two stars move around center of mass?

When one star is approaching us relative to the center of mass, the other star is receding from us.In the top left illustration, star A is moving toward us, so the line in its spectrum is Doppler-shifted toward the blue end of the spectrum. Star B is moving away from us, so its line shows a redshift. When we observe the composite spectrum of the two stars, the line appears double. When the two stars are both moving across our line of sight (neither away from nor toward us), they both have the same radial velocity (that of the pair's center of mass); hence, the spectral lines of the two stars come together.

how does the 21 centimeter line form?

When the electron in a hydrogen atom is in the orbit closest to the nucleus, the proton and the electron may be spinning either (a) in the same direction or (b) in opposite directions. When the electron flips over, the atom gains or loses a tiny bit of energy by either absorbing or emitting electromagnetic energy with a wavelength of 21 centimeters.

The second method for indirect detection of exoplanets: brightness

When the orbital plane of the planet is tilted or inclined so that it is viewed edge-on, we will see the planet cross in front of the star once per orbit, causing the star to dim slightly; this event is known as transit. Figure 21.19 shows a sketch of the transit at three time steps: (1) out of transit, (2) the start of transit, and (3) full transit, along with a sketch of the light curve, which shows the drop in the brightness of the host star. The amount of light blocked—the depth of the transit—depends on the area of the planet (its size) compared to the star. If we can determine the size of the star, the transit method tells us the size of the planet.

what is the difference between florescence and H11 regions?

When you turn on the current, electrons collide with atoms of mercury vapor in the tube. The mercury is excited to a high-energy state because of these collisions. When the electrons in the mercury atoms return to lower-energy levels, some of the energy they emit is in the form of ultraviolet photons. These, in turn, strike a phosphor-coated screen on the inner wall of the light tube. The atoms in the screen absorb the ultraviolet photons and emit visible light as they cascade downward among the energy levels. (The difference is that these atoms give off a wider range of light colors, which mix to give the characteristic white glow of fluorescent lights, whereas the hydrogen atoms in an H II region give off a more limited set of colors.)

why do dust clouds glow brightly in the infrared?

While dust clouds are too cold to radiate a measurable amount of energy in the visible part of the spectrum, they glow brightly in the infrared (Figure 20.11). The reason is that small dust grains absorb visible light and ultraviolet radiation very efficiently. The grains are heated by the absorbed radiation, typically to temperatures from 10 to about 500 K, and re-radiate this heat at infrared wavelengths.

why is infrared better at detecting nebulas?

With near-infrared radiation, we can see more detail within the dusty nebula since infrared can penetrate dust more easily than can visible light.

what is a spectrometer?

a device that spreads light into its different colorsUpon leaving the opposite face of the prism, the light is bent again and further dispersed. If the light leaving the prism is focused on a screen, the different wavelengths or colors that make up white light are lined up side by side just like a rainbow

Instead of observing the evolution of a single star, we can look at

a group or cluster of stars. We look for a group of stars that is very close together in space, held together by gravity, often moving around a common center. Then it is reasonable to assume that the individual stars in the group all formed at nearly the same time, from the same cloud, and with the same composition. We expect that these stars will differ only in mass. And their masses determine how quickly they go through each stage of their lives.Since stars with higher masses evolve more quickly, we can find clusters in which massive stars have already completed their main-sequence phase of evolution and become red giants, while stars of lower mass in the same cluster are still on the main sequence, or even—if the cluster is very young—undergoing pre-main- sequence gravitational contraction. We can see many stages of stellar evolution among the members of a single cluster, and we can see whether our models can explain why the H-R diagrams of clusters of different ages look the way they do.

why does it mean when saying "energy is emitted when the electron does a flip?"

a hydrogen atom consists of a proton and an electron bound together. Both the proton and the electron act is if they were spinning like tops, and spin axes of the two tops can either be pointed in the same direction (aligned) or in opposite directions (anti-aligned). If the proton and electron were spinning in opposite directions, the atom as a whole would have a very slightly lower energy than if the two spins were alignedIf an atom in the lower-energy state (spins opposed) acquired a small amount of energy, then the spins of the proton and electron could be aligned, leaving the atom in a slightly excited state. If the atom then lost that same amount of energy again, it would return to its ground state. The amount of energy involved corresponds to a wave with a wavelength of 21 centimeters; hence, it is known as the 21-centimeter line.

to remove five electrons from their orbits around an oxygen nucleus requires....

a lot of energy. Subsequent observations with orbiting X-ray telescopes revealed that the Galaxy is filled with numerous bubbles of X-ray-emitting gas. To emit X-rays, and to contain oxygen atoms that have been ionized five times, gas must be heated to temperatures of a million degrees or more.

Explain a lunar eclipse

a lunar eclipse is visible to everyone who can see the Moon. Because a lunar eclipse can be seen (weather permitting) from the entire night side of Earth, lunar eclipses are observed far more frequently from a given place on Earth than are solar eclipsesAn eclipse of the Moon is total only if the Moon's path carries it though Earth's umbra. If the Moon does not enter the umbra completely, we have a partial eclipse of the Moon.because Earth is larger than the Moon, its umbra is larger, so that lunar eclipses last longer than solar eclipsesThe Moon is opposite the Sun, which means the Moon will be in full phase before the eclipse, making the darkening even more dramatic.As the Moon begins to dip into the shadow, the curved shape of Earth's shadow upon it soon becomes apparent.Moon is red == sunlight that has been bent into Earth's shadowFor an eclipse where the Moon goes through the center of Earth's shadow, each partial phase consumes at least 1 hour, and totality can last as long as 1 hour and 40 minutes.Not dangerous to look atOn arrival, make sure the scene is saved enter, and then perform a rapid scan of the patient, noting whether any blood or bodily fluids are present period select the proper PPE according to the task you are likely to perform. Typically, globally used for all patient Contacts.

If the neutron star and its companion are positioned the right way,....

a significant amount of material can be transferred to the neutron star and can set it spinning faster (as spin energy is also transferred). The radius of the neutron star would also decrease as more mass was added. Astronomers have found pulsars in binary systems that are spinning at a rate of more than 500 times per second! (These are sometimes called millisecond pulsars since the pulses are separated by a few thousandths of a second.)Such a rapid spin could not have come from the birth of the neutron star; it must have been externally caused. (Recall that the Crab Nebula pulsar, one of the youngest pulsars known, was spinning "only" 30 times per second.) Indeed, some of the fast pulsars are observed to be part of binary systems, while others may be alone only because they have "fully consumed" their former partner stars through the mass transfer process. (These have sometimes been called " black widow pulsars.")

The collapse that takes place when electrons are...

absorbed into the nuclei is very rapid. In less than a second, a core with a mass of about 1 MSun, which originally was approximately the size of Earth, collapses to a diameter of less than 20 kilometers. The speed with which material falls inward reaches one-fourth the speed of light. The collapse halts only when the density of the core exceeds the density of an atomic nucleus (which is the densest form of matter we know). A typical neutron star is so compressed that to duplicate its density, we would have to squeeze all the people in the world into a single sugar cube! This would give us one sugar cube's worth (one cubic centimeter's worth) of a neutron star.The neutron degenerate core strongly resists further compression, abruptly halting the collapse. The shock of the sudden jolt initiates a shock wave that starts to propagate outward. However, this shock alone is not enough to create a star explosion. The energy produced by the outflowing matter is quickly absorbed by atomic nuclei in the dense, overlying layers of gas, where it breaks up the nuclei into individual neutrons and protons.

what does the downward-flowing cool material acts as a....

acts as a kind of plug that block the upward flow of hot material, which is then diverted sideways and eventually reaches the solar surface in the region around the sunspot. This outward flow of hot material accounts for the paradox that we described in The Sun: A Garden-Variety Star—namely, that the Sun emits slightly more energy when more of its surface is covered by cool sunspots.

When does the sun rise from March through September in the North Pole?

all celestial objects that are north of the celestial equator are always above the horizon and, as Earth turns, circle around parallel to it. The Sun is north of the celestial equator from about March 21 to September 21, so at the North Pole, the Sun rises when it reaches the vernal equinox and sets when it reaches the autumnal equinox. Each year there are 6 months of sunshine at each pole, followed by 6 months of darkness.

what happens to the doppler effect when the light source is moving?

all light waves travel at the speed of lightthis means that motion cannot affect the speed, but only the wavelength and the frequency. As the wavelength decreases, the frequency must increase. If the waves are shorter, more will be able to move by during each second

why is the speed of light is such a natural unit of distance for astronomers?

almost all the information we receive is in the form of the light

Explain the resulting effects on tides (what happens in the water?)

an actual flow of water over Earth's surface toward the two regions below and opposite the Moon, causing the water to pile up to greater depths at those placesThe rotation of Earth would carry an observer at any given place alternately into regions of deeper and shallower water.An observer being carried toward the regions under or opposite the Moon, where the water was deepest, would say, "The tide is coming in"; when carried away from those regions, the observer would say, "The tide is going out."During a day, the observer would be carried through two tidal bulges (one on each side of Earth) and so would experience two high tides and two low tides.The actual tides we experiences are a combo of the large effect of the Moon & the smaller effect of the SunWhen sun & moon are lines up = new or full moon = tides produces reinforce each other and are greater than normal

The protostar and disk at this stage are embedded in

an envelope of dust and gas from which material is still falling onto the protostar. This dusty envelope blocks visible light, but infrared radiation can get through. As a result, in this phase of its evolution, the protostar itself is emitting infrared radiation and so is observable only in the infrared region of the spectrum. Once almost all of the available material has been accreted and the central protostar has reached nearly its final mass, it is given a special name: it is called a T Tauri star, named after one of the best studied and brightest members of this class of stars, which was discovered in the constellation of Taurus. (Astronomers have a tendency to name types of stars after the first example they discover or come to understand. It's not an elegant system, but it works.) Only stars with masses less than or similar to the mass of the Sun become T Tauri stars. Massive stars do not go through this stage,

descrie proxima centauri?

an example of the most common type of star, and our most common type of stellar neighbor (as we saw in Stars: A Celestial Census.) Low-mass red M dwarfs make up about 70% of all stars and dominate the census of stars within 10 parsecs (33 light-years) of the Sun.if you wanted to see an M dwarf with your naked eye, you would be out of luck. These stars only produce a fraction of the Sun's light, and nearly all of them require a telescope to be detected.

what happens in stars hotter than the sun?

another set of reactions, called the carbon-nitrogen-oxygen (CNO) cycle, accomplishes the same net result. In the CNO cycle, carbon and hydrogen nuclei collide to initiate a series of reactions that form nitrogen, oxygen, and ultimately, helium. The nitrogen and oxygen nuclei do not survive but interact to form carbon again. Therefore, the outcome is the same as in the proton-proton chain: four hydrogen atoms disappear, and in their place, a single helium atom is created. The CNO cycle plays only a minor role in the Sun but is the main source of energy for stars with masses greater than about the mass of the Sun

what is a parallax? What is a stellar parallax?

apparent shift in the directions of an object as a result of the motion of the observer-> shift in direction of a stars due to Earth's orbital motion = stellar parallax

what is retrograde motion?

apparent westward motion of a planet as Earth swings between it and the Sun (more difficult to explains back when Earth was considered unmoving and Greek only believed in circular celestial motion--> Ptolemy had to work with this!)

Most stars actually generate more energy each second when they

are fusing hydrogen in the shell surrounding the helium core than they did when hydrogen fusion was confined to the central part of the star; thus, they increase in luminosity. With all the new energy pouring outward, the outer layers of the star begin to expand, and the star eventually grows and grows until it reaches enormous proportions

describe the atoms in a hot gas

are moving at high speeds and continually colliding with one another and with any loose electronshey can be excited (electrons moving to a higher level) and de-excited (electrons moving to a lower level) by these collisions as well as by absorbing and emitting light.

what is the area of aperture?

area of circleA = pi * r^2or .25pid^2

what is stellar convection?

as currents of hot gas flow up and down through the star (Figure 16.12). Such currents travel at moderate speeds and do not upset the overall stability of the star. They don't even result in a net transfer of mass either inward or outward because, as hot material rises, cool material falls and replaces it. This results in a convective circulation of rising and falling cells as seen in Figure 16.12. In much the same way, heat from a fireplace can stir up air currents in a room, some rising and some falling, without driving any air into or out the room. Convection currents carry heat very efficiently outward through a star. In the Sun, convection turns out to be important in the central regions and near the surface.

electrons moving energy level: why is it easier to see electromagnetic radiation as photons

as electrons move from one level to another, they give off or absorb little packets of energy. When an electron moves to a higher level, it absorbs a photon of just the right energy (provided one is available). When it moves to a lower level, it emits a photon with the exact amount of energy it no longer needs in its "lower-cost living situation."E=hf h = 6.626 *10^-34 JsHigher-energy photons correspond to higher-frequency waves (which have a shorter wavelength); lower-energy photons are waves of lower frequency.

explain the propagation of light

as the same expanding shell of light covers a larger and larger area, there must be less and less of it in any given place.****Light (and all other electromagnetic radiation) gets weaker and weaker as it gets farther from its source.The increase in the area that the light must cover is proportional to the square of the distance that the light has traveled-- ****inverse square law for light propagation

how did ptolemy solve retrograde motion?

assuming a stationary Earth.Ptolemy solved this problem by having each planet revolve in a small orbit called an epicycle which revolved around each in deferment because earth was considered unmoving Ptolemy had to introduce inform circular movement around another axis called the equant point ( model accepted in Muslim world and later in Christian

in order to address the mystery of the absent companion stars...

astronomers have recently begun to investigate alternative mechanisms of generating type Ia supernovae. All proposed mechanisms rely upon white dwarfs composed of carbon and oxygen, which are needed to meet the observed absence of hydrogen in the type Ia spectrum. And because any isolated white dwarf below the Chandrasekhar mass is stable, all proposed mechanisms invoke a binary companion to explode the white dwarf. The leading alternative mechanism scientists believe creates a type Ia supernova is the merger of two white dwarf stars in a binary system. The two white dwarfs may have unstable orbits, such that over time, they would slowly move closer together until they merge. If their combined mass is greater than the Chandrasekhar limit, the result could also be a type Ia supernova explosion

how to detect using infrared spectrum?

astronomers must protect the infrared detector from nearby radiation, just as you would shield photographic film from bright daylight. Since anything warm radiates infrared energy, the detector must be isolated in very cold surroundings; often, it is held near absolute zero (1 to 3 K) by immersing it in liquid helium. The second step is to reduce the radiation emitted by the telescope structure and optics, and to block this heat from reaching the infrared detector.

What is the mean standard time? Why is this still not reliable?

based on the average value of the solar day over the course of the year--> contains exactly 24 hours--> still inconvenient determined by position of the SunFor example, noon occurs when the Sun is highest in the sky on the meridian (but not necessarily at the zenith). But because we live on a round Earth, the exact time of noon is different as you change your longitude by moving east or west.

Williamina Fleming devised a system to classify stars.....

based on the strength of hydrogen absorption lines. Spectra with the strongest lines were classified as "A" stars, the next strongest "B," and so on down the alphabet to "O" stars, in which the hydrogen lines were very weak. But we saw above that hydrogen lines alone are not a good indicator for classifying stars, since their lines disappear from the visible light spectrum when the stars get too hot or too cold.

What is Gustav Kirchoff's contribution ?

became the first person to use spectroscopy to identify an element in the Sun when he found the spectral signature of sodium gas. In the years that followed, astronomers found many other chemical elements in the Sun and stars. In fact, the element helium was found first in the Sun from its spectrum and only later identified on Earth.

why is difficult to plot an H-R diagram?

because most stars are so faint that we cannot see those outside our immediate neighborhood. The stars plotted in Figure 18.14 were selected because their distances are known. This sample omits many intrinsically faint stars that are nearby but have not had their distances measured, so it shows fewer faint main- sequence stars than a "fair" diagram would.

What is refraction?

bending of light passing through air or water that allow us to see little over the horizon the Sun appears to rise earlier and to set later than it would if no atmosphere were present

what are brighter-appears cepheids?

brighter-appearing cepheids always have the longer periods of light variation. Thus, she reasoned, the period must be related to the luminosity of the stars. When Leavitt did this work, the distance to the Magellanic Clouds was not known, so she was only able to show that luminosity was related to period. She could not determine exactly what the relationship is.To define the period-luminosity relation with actual numbers (to calibrate it), astronomers first had to measure the actual distances to a few nearby cepheids in another way. (This was accomplished by finding cepheids associated in clusters with other stars whose distances could be estimated from their spectra, as discussed in the next section of this chapter.) But once the relation was thus defined, it could give us the distance to any cepheid, wherever it might be located

Dusty clouds in space betray their presence in several ways:

by blocking the light from distant stars, by emitting energy in the infrared part of the spectrum, by reflecting the light from nearby stars, and by making distant stars look redder than they really are.

how can we calculates the energy these reactions generate?

by calculating the difference in the initial and final masses.he masses of hydrogen and helium atoms in the units normally used by scientists are 1.007825 u and 4.00268 u, respectively. (The unit of mass, u, is defined to be 1/12 the mass of an atom of carbon, or approximately the mass of a proton.) Here, we include the mass of the entire atom, not just the nucleus, because electrons are involved as well. When hydrogen is converted into helium, two positrons are created (remember, the first step happens twice), and these are annihilated with two free electrons, adding to the energy produced.4 × 1.007825 = 4.03130 u (mass of initial hydrogen atoms) − 4.00268 u (mass of final helium atoms)= 0.02862 u (mass lost in the transformation)The mass lost, 0.02862 u, is 0.71% of the mass of the initial hydrogen. Thus, if 1 kilogram of hydrogen is converted into helium, then the mass of the helium is only 0.9929 kilograms, and 0.0071 kilograms of material is converted into energy. The speed of light (c) is 3 × 108 meters per second, so the energy released by the conversion of just 1 kilogram of hydrogen into helium is:E=mc2E = .0071 kg ( 3 10^8 m/s)^2 = 6.4 * 10^14 J

how are radio waves reflected?

by conducting surfaces, just as light is reflected from a shiny metallic surface, and according to the same laws of optics. A radio-reflecting telescope consists of a concave metal reflector (called a dish), analogous to a telescope mirror. The radio waves collected by the dish are reflected to a focus, where they can then be directed to a receiver and analyzed.

When nuclear reactions stop, the core of a massive star is supported.....

by degenerate electrons, just as a white dwarf is. For stars that begin their evolution with masses of at least 10 MSun, this core is likely made mainly of iron. (For stars with initial masses in the range 8 to 10 MSun, the core is likely made of oxygen, neon, and magnesium, because the star never gets hot enough to form elements as heavy as iron. The exact composition of the cores of stars in this mass range is very difficult to determine because of the complex physical characteristics in the cores, particularly at the very high densities and temperatures involved.)

how can Gamma-ray detections be made from earths' surface?

by using the atmosphere as the primary detector. When a gamma ray hits our atmosphere, it accelerates charged particles (mostly electrons) in the atmosphere. Those energetic particles hit other particles in the atmosphere and give off their own radiation. The effect is a cascade of light and energy that can be detected on the ground. The VERITAS array in Arizona and the H.E.S.S. array in Namibia are two such ground-based gamma-ray observatories.

what happens to electrons that are captured by the hydrogen nuclei?

cascade down through the various energy levels of the hydrogen atoms on their way to the lowest level, or ground state. During each transition downward, they give up energy in the form of light. The process of converting ultraviolet radiation into visible light is called fluorescence.Interstellar gas contains other elements besides hydrogen. Many of them are also ionized in the vicinity of hot stars; they then capture electrons and emit light, just as hydrogen does, allowing them to be observed by astronomers. But generally, the red hydrogen line is the strongest, and that is why H II regions look red.

why do we need bigger and bigger telescopes?

celestial objects—such as planets, stars, and galaxies—send much more light to Earth than any human eye (with its tiny opening) can catch, and bigger telescopes can detect fainter objects.

What are pulsating variable stars?

cepheid and RR Lyrae variables, both of which are pulsating variable stars.Such a star actually changes its diameter with time—periodically expanding and contracting, as your chest does when you breathe.

Neutral hydrogen atoms can acquire small amounts of energy through...

collisions with other hydrogen atoms or with free electrons. Such collisions are extremely rare in the sparse gases of interstellar space. An individual atom may wait centuries before such an encounter aligns the spins of its proton and electron. Nevertheless, over many millions of years, a significant fraction of the hydrogen atoms are excited by a collision. (Out there in cold space, that's about as much excitement as an atom typically experiences.)

what is an interferometer array

combination of multiple radio dishes to, in effect, work like a large number of two-dish interferometers

describe the structure of molecular cloud structure?

complex filamentary structure, similar to cirrus clouds in Earth's atmosphere, but much less dense. The molecular cloud filaments can be up to 1000 light-years long. Within the clouds are cold, dense regions with typical masses of 50 to 500 times the mass of the Sun; we give these regions the highly technical name clumps. Within these clumps, there are even denser, smaller regions called cores. The cores are the embryos of stars. The conditions in these cores—low temperature and high density—are just what is required to make stars.

what is stellar wind?

consists mainly of protons (hydrogen nuclei) and electrons streaming away from the star at speeds of a few hundred kilometers per second (several hundred thousand miles per hour). When the wind first starts up, the disk of material around the star's equator blocks the wind in its direction. Where the wind particles can escape most effectively is in the direction of the star's poles.

differences in absorption spectrum

consists of a series or pattern of dark lines—missing colors—superimposed upon the continuous spectrum of a sourceIn contrast, absorption spectra occur when passing white light through a cool, thin gas. The temperature and other conditions determine whether the lines are bright or dark (whether light is absorbed or emitted), but the wavelengths of the lines for any element are the same in either case. It is the precise pattern of wavelengths that makes the signature of each element unique

the Orion molecular cloud:what happens in regions of star formation by considering a nearby site where stars are forming?

constellation of Orion, The Hunter, about 1500 light- years awayThe Orion molecular cloud is much larger than the star pattern and is truly an impressive structure. In its long dimension, it stretches over a distance of about 100 light-years. The total quantity of molecular gas is about 200,000 times the mass of the Sun. Most of the cloud does not glow with visible light but betrays its presence by the radiation that the dusty gas gives off at infrared and radio wavelengths.

what is the composition of cold interstellar stars?

contain cyanoacetylene (HC3N) and acetaldehyde (CH3CHO), generally regarded as starting points for amino acid formation. These are building blocks of proteins, which are among the fundamental chemicals from which living organisms on Earth are constructed

what happens after forming iron ?

content being iron; it requires payment (must absorb energy) to change its stable nuclear structure. This is the exact opposite of what has happened in each nuclear reaction so far: instead of providing energy to balance the inward pull of gravity, any nuclear reactions involving iron would remove some energy from the core of the star.Unable to generate energy, the star now faces catastrophe.

would the contractions of the sun be able to maintain the rate of energy production for a long time?

contraction of the Sun at a rate of only about 40 meters per year would be enough to produce the amount of energy that it is now radiating.-->the decrease in the Sun's size from such a slow contraction would be undetectable.--> we can calculate how much energy has been radiated by the Sun during its entire lifetime as it has contracted from a very large diameter to its present size.--> sun 4 * 10^26 watts = 100 million years

what was the purpose of ancient observatories?

could measure the positions of celestial objects, mostly to keep track of time and date--> religious and ritualistic functions-->only used eye and written records

the rate at which ions and electrons recombine depends on what?

depends on their relative speeds/tempalso depends on density,he higher the density, the greater the chance for recapture, because the different kinds of particles are crowded more closely together

How is latitude and longitude measured in the sky?

declination (latitude) and right ascension ( longitude) to measure positions in the skysky appears to rotate about points above the North and South Poles of Earth—points in the sky called the north celestial pole and the south celestial pole. the celestial equator is the middle - 90 degrees from the poles

what does the resolution of the interferometer depend on?

depends upon the separation of the telescopes, not upon their individual apertures. Two telescopes separated by 1 kilometer provide the same resolution as would a single dish 1 kilometer across (although they are not, of course, able to collect as much radiation as a radio-wave bucket that is 1 kilometer across).

why determines the light gathering ability of a telescope?

determined by the area of the device acting as the light-gathering "bucket."

What is aperture?

diameter of the opening through which light travels or reflectsbigger apertures = greater light capturing power

what is the color Index

difference between the magnitudes of a star or other object measured in light of two different spectral regions—for example, blue minus visual (B-V) magnitudes

What causes lunar phases?

different appearances with the Moon starting dark and getting more and more illuminated by sunlight over the course of two weeks --> moon disks fade becoming dark again two weeks later *** depends on what part of the moon we see illuminated

for visible light, we perceive different wavelengths as....

different colors: red, for example, is the longest visible wavelength, and violet is the shortest.

what are spectral signatures?

different substances showed distinctive spectral signatures by which their presence could be detected unique pattern of colors for each type of atom (its spectrum) can help us identify which element or elements are in a gas

what did Mizar show on the spectrum about binary stars?

discovered a second class of binary stars in 1889—a class in which only one of the stars is actually seen directly. He was examining the spectrum of Mizar and found that the dark absorption lines in the brighter star's spectrum were usually double. Not only were there two lines where astronomers normally saw only one, but the spacing of the lines was constantly changing. At times, the lines even became single. Pickering correctly deduced that the brighter component of Mizar, called Mizar A, is itself really two stars that revolve about each other in a period of 104 days.

what are double stars?

discovered in 1650, less than half a century after Galileo began to observe the sky with a telescope. John Baptiste Riccioli (1598-1671), an Italian astronomer, noted that the star Mizar, in the middle of the Big Dipper's handle, appeared through his telescope as two stars.

What is J.J. Thomson known for?

discovered the electron—> flow of this causes electricity

what is an energy level? what happens when you drop a level? go up a level?

each of the permitted electron orbits around a given atom has a certain energy valueto move from one orbit to another require's a change in energyIf the electron goes to a lower level, the energy difference will be given off; if the electron goes to a higher level, the energy difference must be obtained from somewhere else.Each jump (or transition) to a different level has a fixed and definite energy change associated with it

What was the implication with the lack of shift in stars that forced the Greeks back to geocentrism?

earth had to be not stationary and or the stellar shift was so small that it was not noticeable so

what is radiation?

energetic photons move away from hot material and are absorbed by some material to which they convey some or all of their energy.You can feel this when you put your hand close to the coils of an electric heater, allowing infrared photons to heat up your hand.the transfer of heat energy by electromagnetic radiation.

X-ray, and gamma-ray astronomy measure....

energy per area per second rather than magnitudes to express the results of their measurements.

describe how temperature impacts the spectra of a star

figure 17.5in the hottest O stars (those with temperatures over 28,000 K), only lines of ionized helium and highly ionized atoms of other elements are conspicuous. Hydrogen lines are strongest in A stars with atmospheric temperatures of about 10,000 K. Ionized metals provide the most conspicuous lines in stars with temperatures from 6000 to 7500 K (spectral type F). In the coolest M stars (below 3500 K), absorption bands of titanium oxide and other molecules are very strong. By the way, the spectral class assigned to the Sun is G2

first step in the process of creating stars is

formation of dense cores within a clump of gas and dustIt is generally thought that all the material for the star comes from the core, the larger structure surrounding the forming star. Eventually, the gravitational force of the infalling gas becomes strong enough to overwhelm the pressure exerted by the cold material that forms the dense cores. The material then undergoes a rapid collapse, and the density of the core increases greatly as a result. During the time a dense core is contracting to become a true star, but before the fusion of protons to produce helium begins, we call the object a protostatr

Maxwell: what if electric changes were oscillating?

found that the resulting pattern of electric and magnetic fields would spread out and travel rapidly through space. --> like a drop striking water and causes a waveatoms and molecules (which consist of charged particles) oscillate back and forth all the time. The resulting electromagnetic disturbances are among the most common phenomena in the universe.

what does amount of energy a photon has depends on ?

frequency--> high freq high energy

what do particles shooting out in opposite directions cause?

from the popular regions of newly formed stars. In many cases, these beams point back to the location of a protostar that is still so completely shrouded in dust that we cannot yet see it

what are elementary particles?

fundamentals of atom = proton, neutron, electronor each kind of particle, there is a corresponding but opposite antiparticle.If the particle carries a charge, its antiparticle has the opposite charge.anti electron = positron

While no energy is being generated within the white dwarf core of the star....

fusion still occurs in the shells that surround the core. As the shells finish their fusion reactions and stop producing energy, the ashes of the last reaction fall onto the white dwarf core, increasing its mass. As Figure 23.2 shows, a higher mass means a smaller core. The core can contract because even a degenerate gas is still mostly empty space. Electrons and atomic nuclei are, after all, extremely small. The electrons and nuclei in a stellar core may be crowded compared to the air in your room, but there is still lots of space between them.

In this section, you were introduced to some very dense objects. How would those objects' gravity affect you?

g = (G × M)/ R^2G= 6.67 * 10 ^-11 m^2/kgs^2g on EARTH = 9.8 m/s^2

What is the raw material for "next generation of stars?"

gas and dust collection to form enormous clouds that become this raw material

What is ptolemy's greatest contribution?

geometric representation of the solar system that predicted the positions of the planes for any desired date and time ( Hipparchus observational material + Ptolemy cosmological model)The complicating factor in explaining the motions of the planets is that their apparent wandering in the sky results from the combination of their own motions with Earth's orbital revolution.

describe the using spectrum to reveal details about space

give evidence of certain chemical elements between us and the Sun absorbing those wavelengths of sunlight. Because the space between us and the Sun is pretty empty, astronomers realized that the atoms doing the absorbing must be in a thin atmosphere of cooler gas around the Sun. This outer atmosphere is not all that different from the rest of the Sun, just thinner and cooler. Thus, we can use what we learn about its composition as an indicator of what the whole Sun is made of.use the presence of absorption and emission lines to analyze the composition of other stars and clouds of gas in space.

the three basic types of clusters astronomers have discovered are

globular clusters, open clusters, and stellar associations

What is Earth's axis?

goes through the North and South pole and tilted at a 23.5 degree angle since the axis runs through the poles they seems to be unmoving

Everything in the universe can be explained by four fources?

gravity, electromagnetism & two forces that act on a nuclear level

what is an ion?

greater amounts of energy must be absorbed by the now-ionized atom (called an ion) to remove an additional electron deeper in the structure of the atom. Successively greater energies are needed to remove the third, fourth, fifth—and so on—electrons from the atom. If enough energy is available, an atom can become completely ionized, losing all of its electrons.

What is helioseismology?

has shown that convection extends inward from the surface 30% of the way toward the center; we have used this information in drawing Figure 16.15. Pulsation measurements also show that the differential rotation that we see at the Sun's surface, with the fastest rotation occurring at the equator, persists down through the convection zone. Below the convection zone, however, the Sun, even though it is gaseous throughout, rotates as if it were a solid body like a bowling ball. Another finding from helioseismology is that the abundance of helium inside the Sun, except in the center where nuclear reactions have converted hydrogen into helium, is about the same as at its surface. That result is important to astronomers because it means we are correct when we use the abundance of the elements measured in the solar atmosphere to construct models of the solar interior.

what are giant molecular clouds?

have densities of hundreds to thousands of atoms per cm3, much denser than interstellar space is on average. As a result, though they account for a very small fraction of the volume of interstellar space, they contain a significant fraction—20-30%—of the total mass of the Milky Way's gas. Because of their high density, molecular clouds block ultraviolet starlight, the main agent for heating most interstellar gas. As a result, they tend to be extremely cold, with typical temperatures near 10 K (−263 °C). Giant molecular clouds are also the sites where new stars form.

What does the refraction allow us to see about the Sun? (What degrees?)

he atmosphere scatters light and provides some twilight illumination even when the Sun is below the horizon. Astronomers define morning twilight as beginning when the Sun is 18° below the horizon, and evening twilight extends until the Sun sinks more than 18° below the horizon

why is the discovery of complex molecules surprising?

he discovery of complex molecules in space came as a surprise because most of interstellar space is filled with ultraviolet light from stars, and this light is capable of dissociating molecules (breaking them apart into individual atoms). In retrospect, however, the presence of molecules is not surprising.

what the brown dwarf spectral classes?

he hottest brown dwarfs are given types L0-L9 (temperatures in the range 2400-1300 K), whereas still cooler (1300-700 K) objects are given types T0-T9

what happens to the doppler effect when the light source is at rest?

he light waves spread out evenly in all directions, like the ripples from a splash in a pond. The crests are separated by a distance, λ, where λ is the wavelength. The observer, who happens to be located in the direction of the bottom of the image, sees the light waves coming nice and evenly, one wavelength apart. Observers located anywhere else would see the same thing.

how is the sun resisted collapse for so long?

he mutual gravitational attraction between the masses of various regions within the Sun produces tremendous forces that tend to collapse the Sun toward its center. Yet we know from the history of Earth that the Sun has been emitting roughly the same amount of energy for billions of years, so clearly it has managed to resist collapse for a very long time. The gravitational forces must therefore be counterbalanced by some other force. That force is due to the pressure of gases within the Sun (Figure 16.11). Calculations show that, in order to exert enough pressure to prevent the Sun from collapsing due to the force of gravity, the gases at its center must be maintained at a temperature of 15 million K. Think about what this tells us. Just from the fact that the Sun is not contracting, we can conclude that its temperature must indeed be high enough at the center for protons to undergo fusion.

what were bohr's suggestion for understanding the hydrogen spectrum?

he suggested that the spectrum of hydrogen can be understood if we assume that orbits of only certain sizes are possible for the electron. Bohr further assumed that as long as the electron moves in only one of these allowed orbits, it radiates no energy: its energy would change only if it moved from one orbit to another.--> became the foundation of quantum mechanics

What are alpha particles?

helium atoms without the electrons and are positively charged

how are objects 1/100 mass of sun planets?

hey may radiate energy produced by the radioactive elements that they contain, and they may also radiate heat generated by slowly compressing under their own weight (a process called gravitational contraction). However, their interiors will never reach temperatures high enough for any nuclear reactions, to take place. Jupiter, whose mass is about 1/1000 the mass of the Sun, is unquestionably a planet, for example

what is the relationship with temp and luminosity?

hotter stars are more luminous than cooler ones.

why does the length of the time that photons require to reach the surface depends on ?

how far a photon on average travels between collisions, and the travel time depends on what model of the complicated solar interior we accept. Estimates are somewhat uncertain but indicate that the emission of energy from the surface of the Sun can lag its production in the interior by 100,000 years to as much as 1,000,000 years.

we could use the difference in their apparent brightnesses to tell us something we very much want to know:

how far away they are.if all the stars had the same luminosity, we could immediately infer that the brightest-appearing stars were close by and the dimmest-appearing ones were far away.

what does a star turning into a white dwarf depend on?

how much mass is lost in the red-giant and earlier phases of evolution. All stars that have masses below the Chandrasekhar limit when they run out of fuel will become white dwarfs, no matter what mass they were born with.

A planet will transit its star only if ....

if Earth lies in the plane of the planet's orbit. If the planets in other systems do not have orbits in the same plane, we are unlikely to see multiple transiting objects. Also, as we have noted before, Kepler was sensitive only to planets with orbital periods less than about 4 years. What we expect from Kepler data, then, is evidence of coplanar planetary systems confined to what would be the realm of the terrestrial planets in our solar system.

how scarce are dust grains in space?

if all the interstellar gas within the Galaxy were spread out smoothly, there would be only about one atom of gas per cm3 in interstellar space.The dust grains are even scarcer. A km3 of space would contain only a few hundred to a few thousand tiny grains, each typically less than one ten-thousandth of a millimeter in diameter. These numbers are just averages, however, because the gas and dust are distributed in a patchy and irregular way, much as water vapor in Earth's atmosphere is often concentrated into clouds.

what is the bohr model's interpretation of energy of electrons?

if the electron moves from one orbit to another closer to the atomic nucleus, it must give up some energy in the form of electromagnetic radiation.If the electron goes from an inner orbit to one farther from the nucleus, however, it requires some additional energy.One way to obtain the necessary energy is to absorb electromagnetic radiation that may be streaming past the atom from an outside source.

is the sun stable?

in equilibrium = neither expanding nor contractingAll the forces within it are balanced, so that at each point within the star, the temperature, pressure, density, and so on are maintained at constant values.

The best observatory sites are those that are

in high, dark dry places far from habitationAndes Mountains of Chile, the desert peaks of Arizona, the Canary Islands in the Atlantic Ocean, and Mauna Kea in Hawaii, a dormant volcano with an altitude of 13,700 feet (4200 meters)

The hydrogen lines in the visible part of the spectrum are strongest?

in stars with intermediate temperatures—not too hot and not too cold. Calculations show that the optimum temperature for producing visible hydrogen lines is about 10,000 K. At this temperature, an appreciable number of hydrogen atoms are excited to the second energy level. They can then absorb additional photons, rise to still-higher levels of excitation, and produce a dark absorption line.*****every other chemical element, in each of its possible stages of ionization, has a characteristic temperature at which it is most effective in producing absorption lines in any particular part of the spectrum.

what deviates from H-R diagram rule?

in the upper-right region, where stars have low temperature and high luminosity. How can a star be at once cool, meaning each square meter on the star does not put out all that much energy, and yet very luminous? The only way is for the star to be enormous—to have so many square meters on its surface that the total energy output is still large. These stars must be giants or supergiants, the stars of huge diameter we discussed earlier.There are also some stars in the lower-left corner of the diagram, which have high temperature and low luminosity. If they have high surface temperatures, each square meter on that star puts out a lot of energy. How then can the overall star be dim? It must be that it has a very small total surface area; such stars are known as white dwarfs (white because, at these high temperatures, the colors of the electromagnetic radiation thatthey emit blend together to make them look bluish-white). We will say more about these puzzling objects in a moment.

While density of interstellar matter is very low, the volume of space...

in which such matter is found is huge, and so its total mass is substantial. To see why, we must bear in mind that stars occupy only a tiny fraction of the volume of the Milky Way Galaxy. For example, it takes light only about four seconds to travel a distance equal to the diameter of the Sun, but more than four years to travel from the Sun to the nearest star. Even though the spaces among the stars are sparsely populated, there's a lot of space out there!

how does the color index?

index of 0 : a star with a surface temperature of about 10,000 K, such as Vega. The B-V color indexes of stars range from −0.4 for the bluest stars, with temperatures of about 40,000 K, to +2.0 for the reddest stars, with temperatures of about 2000 K. The B-V index for the Sun is about +0.65.the B-V index is always the "bluer" minus the "redder" color.

What is a nebula?

interstellar material is concentrated into giant clouds, each of which is known as a nebula (plural "nebulae," Latin for "clouds"). The best-known nebulae are the ones that we can see glowing or reflecting visible light

why is the discovery of complex molecules NOT surprising?

interstellar space also contains significant amounts of dust capable of blocking out starlight. When this dust accumulates in a single location, the result is a dark cloud where ultraviolet starlight is blocked and molecules can survive. The largest of these structures are created where gravity pulls interstellar gas together to form giant molecular clouds, structures as massive as a million times the mass of the Sun. Within these, most of the interstellar hydrogen has formed the molecule H2 (molecular hydrogen). Other, more complex molecules are also present in much smaller quantities.

how is polaris a cepheid variable?

is a cepheid variable that, for a long time, varied by one tenth of a magnitude, or by about 10% in visual luminosity, in a period of just under 4 days. Recent measurements indicate that the amount by which the brightness of Polaris changes is decreasing and that, sometime in the future, this star will no longer be a pulsating variable. This is just one more piece of evidence that stars really do evolve and change in fundamental ways as they age, and that being a cepheid variable represents a stage in the life of the star.

what are stellar associations?

is a group of extremely young stars, typically containing 5 to 50 hot, bright O and B stars scattered over a region of space some 100-500 light-years in diameter.As an example, most of the stars in the constellation Orion form one of the nearest stellar associations. Associations also contain hundreds to thousands of low-mass stars, but these are much fainter and less conspicuous. The presence of really hot, luminous stars indicates that star formation in the association has occurred in the last million years or so. Since O stars go through their entire lives in only about a million years, they would not still be around unless star formation has occurred recently. It is therefore not surprising that associations are found in regions rich in the gas and dust required to form new stars. It's like a brand new building still surrounded by some of the construction materials used to build it and with the landscape still showing signs of construction. On the other hand, because associations, like ordinary open clusters, lie in regions occupied by dusty interstellar matter, many are hidden from our view.

What is the ionosphere?

is a layer of charged particles at the top of our atmosphere, produced by interactions with sunlight and charged particles that are ejected from the Sun

what is interference?

is a technical term for the way that multiple waves interact with each other when they arrive in our instruments, and this interaction allows us to coax more detail out of our observations.

what is a lens?

is a transparent piece of material that bends the rays of light passing through it. If the light rays are parallel as they enter, the lens brings them together in one place to form an image (Figure 6.4). If the curvatures of the lens surfaces are just right, all parallel rays of light (say, from a star) are bent, or refracted, in such a way that they converge toward a point, called the focus of the lens.

where is the mass of the universe concentrated?

is equal to about 15% of the mass contained in stars. This means that the mass of the interstellar matter in our Galaxy amounts to about 10billion times the mass of the Sun. There is plenty of raw material in the Galaxy to make generations of new stars and planets

the velocity of one of the oscillating regions on the Sun.....

is only a few hundred meters per second, and it takes about 5 minutes to complete a full cycle from maximum to minimum velocity and back again. The change in the size of the Sun measured at any given point is no more than a few kilometers.

what are problems with refractor telescopes?

is that the light must pass through the lens of a refractor. That means the glass must be perfect all the way through, and it has proven very difficult to make large pieces of glass without flaws and bubbles in themoptical properties of transparent materials change a little bit with the wavelengths (or colors) of light, so there is some additional distortion= chromatic aberrationsince the light must pass through the lens, the lens can only be supported around its edges (just like the frames of our eyeglasses). The force of gravity will cause a large lens to sag and distort the path of the light rays as they pass through it.because the light passes through it, both sides of the lens must be manufactured to precisely the right shape in order to produce a sharp image

nearest star visible without a telescope from most of the United States

is the brightest appearing of all the stars, Sirius, which has a distance of a little more than 8 light-years. It too is a binary system, composed of a faint white dwarf orbiting a bluish-white, main-sequence star. It is an interesting coincidence of numbers that light reaches us from the Sun in about 8 minutes and from the next brightest star in the sky in about 8 years.

What is declination? (what is Polaris's declination?)

is the latitude in the sky (north or south) polaris is the closest to 90 degrees

what is the interval between two transits?

is the length of the year for that planet, which can be used (again using Kepler's laws) to find its distance from the star. Larger planets like Jupiter block out more starlight than small earthlike planets, making transits by giant planets easier to detect, even from ground-based observatories. But by going into space, above the distorting effects of Earth's atmosphere, the transit technique has been extended to exoplanets as small as Mars.

what is the the strongest line in the visible region of the hydrogen spectrum

is the red line in the Balmer series this emission line accounts for the characteristic red glow

what is a radar?

is the technique of transmitting radio waves to an object in our solar system and then detecting the radio radiation that the object reflects back.we can measure time with precision and because we know the speed at which radio waves travel (the speed of light), we can determine the distance to the object or a particular feature on its surface (such as a mountain)

Another way to overcome the blurring effect of Earth's atmosphere is to...

is to observe from space. Infrared may be the optimal wavelength range in which to observe because planets get brighter in the infrared while stars like our Sun get fainter, thereby making it easier to detect a planet against the glare of its star. Special optical techniques can be used to suppress the light from the central star and make it easier to see the planet itself. However, even if we go into space, it will be difficult to obtain images of Earth-size planets.

explain why prism refracts light

isaac Newton described an experiment in which he permitted sunlight to pass through a small hole and then through a prism. Newton found that sunlight, which looks white to us, is actually made up of a mixture of all the colors of the rainbowThe bending of the beam depends on the wavelength of the light as well as the properties of the material, and as a result, different wavelengths (or colors of light) are bent by different amounts and therefore follow slightly different paths through the prism. The violet light is bent more than the red.--> dispersion

If a white dwarf accumulates matter from a companion star at a much faster rate,

it can be pushed over the Chandrasekhar limit. The evolution of such a binary system is shown in Figure 23.18. When its mass approaches the Chandrasekhar mass limit (exceeds 1.4 MSun), such an object can no longer support itself as a white dwarf, and it begins to contract. As it does so, it heats up, and new nuclear reactions can begin in the degenerate core. The star "simmers" for the next century or so, building up internal temperature. This simmering phase ends in less than a second, when an enormous amount of fusion (especially of carbon) takes place all at once, resulting in an explosion. The fusion energy produced during the final explosion is so great that it completely destroys the white dwarf. Gases are blown out into space at velocities of about 10,000 kilometers per second, and afterward, no trace of the white dwarf remains.

What is a Great Circle ?

it is a circle on a sphere on which has a center in the same place as a sphere --> the celestial equator is a great circle as well the multiple circle that can be formed between North & South pole

what is active control?

it is possible to measure that sag many times each second and apply forces at 120 different locations to the back of the mirror to correct the sag, a process called active control

what happens when light is reflected over a page and enter the human eye?

its changing electric and magnetic fields stimulate nerve endings, which then transmit the information contained in these changing fields to the brainscience of astronomy is primarily about analyzing radiation from distant objects to understand what they are and how they work

What are Cepheid variables?

large, yellow, pulsating stars named for the first-known star of the group, Delta Cephei (a whole class of stars is named after the constellation in which the first one happened to be found.)The star rises rather rapidly to maximum light and then falls more slowly to minimum light, taking a total of 5.4 days for one cycle.Most cepheids have periods in the range of 3 to 50 days and luminosities that are about 1000 to 10,000 times greater than that of the Sun. Their variations in luminosity range from a few percent to a factor of 10.

what is latitude and how is it measured?

latitude is the north-south location is the number of degrees on the arc north(positive) or south (negative) from the equator along the meridian north pole is +90 and equator is 0 measured 0-90 degrees

What is the celestial equator?

lies between the north and south pole the north and south pole are at the a 90 degree angle from the zenith

how do we know how far away stars are ?

light fades with increasing distance. The energy we receive is inversely proportional to the square of the distance. If, for example, we have two stars of the same luminosity and one is twice as far away as the other, it will look four times dimmer than the closer one. If it is three times farther away, it will look nine (three squared) times dimmer, and so forth.

What is the Prime Meridian (why this location?)

longitude: 0 degrees Located in Greenwich England Choose this because longitude was most prominently being studied in USA and England and this was a point between them

what were kepler discoveries?

many rocky, Earth-size planets, far more than Jupiter- size gas planets. This immediately tells us that the initial Doppler discovery of many hot Jupiters was a biased sample, in effect, finding the odd planetary systems because they were the easiest to detect. However, there is one huge difference between this observed size distribution and that of planets in our solar system. The most common planets have radii between 1.4 and 2.8 that of Earth, sizes for which we have no examples in the solar system. These have been nicknamed super-Earths, while the other large group with sizes between 2.8 and 4 that of Earth are often called mini-Neptunes.

what does color indicate about a star's temperature?

many stars give off most of their energy in visible light, the color of light that dominates a star's appearance is a rough indicator of its temperature. If one star looks red and another looks blue, which one has the higher temperature? Because blue is the shorter-wavelength color, it is the sign of a hotter star.

where is most of sun's energy generated?

nearly all of the Sun's energy is generated within about 150,000 kilometers of its core, or within less than 10% of its total volume.

what does the Measurements of the widths of spectral lines show that stars rotation with respect to the sun?

many stars rotate faster than the Sun, some with periods of less than a day! These rapid rotators spin so fast that their shapes are "flattened" into what we call oblate spheroids. An example of this is the star Vega, which rotates once every 12.5 hours. Vega's rotation flattens its shape so much that its diameter at the equator is 23% wider than its diameter at the polesThe Sun, with its rotation period of about a month, rotates rather slowly. Studies have shown that stars decrease their rotational speed as they age. Young stars rotate very quickly, with rotational periods of days or less. Very old stars can have rotation periods of several months.

when is a star in "crisis?"

mass like the Sun's just after it had climbed up to the red-giant region of the H-R diagram for a second time and had shed some of its outer layers to form a planetary nebula. Recall that during this time, the core of the star was undergoing an "energy crisis." Earlier in its life, during a brief stable period, helium in the core had gotten hot enough to fuse into carbon (and oxygen). But after this helium was exhausted, the star's core had once more found itself without a source of pressure to balance gravity and so had begun to contract.

How is resolution measured?

measured in units of angle on the sky, typically in units of arc secondsOne arcsecond is 1/3600 degree, and there are 360 degrees in a full circle.

how do more precisely measure star temperature?

measuring how much energy a star gives off at each wavelength and by constructing diagrams like (pic)The location of the peak (or maximum) in the power curve of each star can tell us its temperature. The average temperature at the surface of the Sun, which is where the radiation that we see is emitted, turns out to be 5800 K.

what is newtons third law & interpretation of the law?

momentum is conserved in an isolated system--> change in momentum is system is balanced by another changeForces occur in pairs and are equal and opposite in natureThings fall toward earth, but the acceleration of our planet is far too small to be measured

What is a solar eclipse?

moon blocking the suns light

So the star becomes simultaneously what?

more luminous and cooler. On the H-R diagram, the star therefore leaves the main-sequence band and moves upward (brighter) and to the right (cooler surface temperature). Over time, massive stars become red supergiants, and lower-mass stars like the Sun become red giants. (We first discussed such giant stars in The Stars: A Celestial Census; here we see how such "swollen" stars originate.) You might also say that these stars have "split personalities": their cores are contracting while their outer layers are expanding. (Note that red giant stars do not actually look deep red; their colors are more like orange or orange-red.)

what happens at the temperature inside the stars with masses smaller than about 1.2 times the mass of our Sun?

most of the energy is produced by the reactions we have just described, and this set of reactions is called the proton-proton chain (or sometimes, the p-p chain). In the proton-proton chain, protons collide directly with other protons to form helium nuclei.

what happens when the ultraviolet protons reach the sun's surface?

most of the photons have given up enough energy to be ordinary light—and they are the sunlight we see coming from our star. (To be precise, each gamma-ray photon is ultimately converted into many separate lower-energy photons of sunlight.) So, the sunlight given off by the Sun today had its origin as a gamma ray produced by nuclear reactions deep in the Sun's core.

what are ultraviolet rays and where are they observed from?

mostly blocked by the ozone layer of Earth's atmosphere, but a small fraction of ultraviolet rays from our Sun do penetrate to cause sunburn or, in extreme cases of overexposure, skin cancer in human beings. Ultraviolet astronomy is also best done from space.

what is the composition of complex molecules?

mostly combinations of hydrogen, oxygen, carbon, nitrogen, and sulfur atoms. Many of these molecules are organic (those that contain carbon and are associated with the carbon chemistry of life on Earth.) They include formaldehyde (used to preserve living tissues), alcohol, and antifreeze.astronomers discovered acetic acid (the prime ingredient of vinegar) in a cloud lying in the direction of the constellation of Sagittarius. To balance the sour with the sweet, a simple sugar (glycolaldehyde) has also been found.

what is responsible for electromagnetic radiation?

motion at the microscopic level As atoms and molecules move about and collide, or vibrate in place, their electrons give off electromagnetic radiation.The characteristics of this radiation are determined by the temperature of those atoms and molecules.In a hot material, for example, the individual particles vibrate in place or move rapidly from collisions, so the emitted waves are, on average, more energetic. And recall that higher energy waves have a higher frequency.

what are the best observation sites?

mountains, far from the lights and pollution of cities.takes place far away, often on desert mountains or isolated peaks in the Atlantic and Pacific Oceans Picking The Best Observing Sites

each time an electron and a proton in the star's core merge to make a neutron, merger releases....

neutrino. These ghostly subatomic particles, introduced in The Sun: A Nuclear Powerhouse, carry away some of the nuclear energy. It is their presence that launches the final disastrous explosion of the star. The total energy contained in the neutrinos is huge. In the initial second of the star's explosion, the power carried by the neutrinos (1046 watts) is greater than the power put out by all the stars in over a billion galaxies.While neutrinos ordinarily do not interact very much with ordinary matter (we earlier accused them of being downright antisocial), matter near the center of a collapsing star is so dense that the neutrinos do interact with it to some degree. They deposit some of this energy in the layers of the star just outside the core. This huge, sudden input of energy reverses the infall of these layers and drives them explosively outward. Most of the mass of the star (apart from that which went into the neutron star in the core) is then ejected outward into space. As we saw earlier, such an explosion requires a star of at least 8 MSun, and the neutron star can have a mass of at most 3 MSun. Consequently, at least five times the mass of our Sun is ejected into space in each such explosive event!

If the remaining mass of the star's core is more than about three times that of the Sun (MSun)... What happens to it ?

no known force can stop it from collapsing forever! Gravity simply overwhelms all other forces and crushes the core until it occupies an infinitely small volume. A star in which this occurs may become one of the strangest objects ever predicted by theory—a black hole.

What are gamma rays?Where are they observed from ?

no longer than 0.01 nanometer--> shortest wavelength--> carry a lot of energyGamma radiation is generated deep in the interior of stars, as well as by some of the most violent phenomena in the universe, such as the deaths of stars and the merging of stellar corpses.**Gamma rays coming to Earth are absorbed by our atmosphere before they reach the ground; thus, they can only be studied using instruments in space.

What is the Pauli Exclusion Principle?

no two electrons can be in the same place at the same time doing the same thing. We specify the place of an electron by its position in space, and we specify what it is doing by its motion and the way it is spinning.

what happens to your weight in the elevator ? as your moving up or down or falling ?

normal weight when unmoving increase weight when moving upward decreased weight when moving down weightlessness when elevator is falling

at lower planet masses

notice that as the mass of these hypothetical planets increases, the radius also increases. That makes sense—if you were building a model of a planet out of clay, your toy planet would increase in size as you added more clay. However, for the highest mass planets (M > 1000 MEarth) in Figure 21.25, notice that the radius stops increasing and the planets with greater mass are actually smaller. This occurs because increasing the mass also increases the gravity of the planet, so that compressible materials (even rock is compressible) will become more tightly packed, shrinking the size of the more massive planet.In reality, planets are not pure compositions like the hypothetical water or iron planet. Earth is composed of a solid iron core, an outer liquid-iron core, a rocky mantle and crust, and a relatively thin atmospheric layer. Exoplanets are similarly likely to be differentiated into compositional layers. The theoretical lines in Figure 21.25 are simply guides that suggest a range of possible compositions.

what forces hold atomic nucleus together?

nuclear force

Most exoplanet detections are made using techniques where we..

observe the effect that the planet exerts on the host star. For example, the gravitational tug of an unseen planet will cause a small wobble in the host star. Or, if its orbit is properly aligned, a planet will periodically cross in front of the star, causing the brightness of the star to dim.

what can we infer from RR lyrae star clusters?

occurring in any particular cluster all have about the same apparent brightness. Since stars in a cluster are all at approximately the same distance, it follows that RR Lyrae variables must all have nearly the same intrinsic luminosity, which turns out to be about 50 LSun. In this sense, RR Lyrae stars are a little bit like standard light bulbs and can also be used to obtain distances, particularly within our Galaxy

what are the most common planet sizes?

of are those with radii from 1 to 3 times that of Earth—what we have called "Earths" and "super-Earths." Each group occurs in about one-third to one-quarter of stars. In other words, if we group these sizes together, we can conclude there is nearly one such planet per star! And remember, this census includes primarily planets with orbital periods less than 2 years. We do not yet know how many undiscovered planets might exist at larger distances from their star.

how can H-R diagram estimates be used to understand lives of stars?

on average, 90% of all stars are located on the main sequence of the H-R diagram. If we can identify some activity or life stage with the main sequence, then it follows that stars must spend 90% of their lives in that activity or life stage.

What is a planet? (What makes it different than a star?)

on object that rotates around a star and does not readily emit light (if it consistently emits light it is a star)

What is a constellation?

one of 88 patterns regions which the astronomers divided the sky into named after the prominent star within it

what is the nuclear force?

only capable of acting over distances about the size of the atomic nucleus.The strong nuclear force is an attractive force, stronger than the electrical force, and it keeps the particles of the nucleus tightly bound together.

which stars appear brightest in the sky?

only six of the 20 stars that appear brightest in our sky— Sirius, Vega, Altair, Alpha Centauri, Fomalhaut, and Procyon—are found within 26 light-years of the Sun

What are the Magellanic Clouds..?

opportunity to study the behavior of variable stars independent of their distance. For all practical purposes, the Magellanic Clouds are so far away that astronomers can assume that all the stars in them are at roughly the same distance from us.If all the variable stars in the Magellanic Clouds are at roughly the same distance, then any difference in their apparent brightnesses must be caused by differences in their intrinsic luminosities.

To be truly representative, the stellar population, an H-R diagram should be plotted...

or all stars within a certain distance. Unfortunately, our knowledge is reasonably complete only for stars within 10 to 20 light-years of the Sun, among which there are no giants or supergiants. Still, from many surveys (and more can now be done with new, more powerful telescopes), we estimate that about 90% of the true stars overall (excluding brown dwarfs) in our part of space are main-sequence stars, about 10% are white dwarfs, and fewer than 1% are giants or supergiants.

how does triangulation work in humans ?

our depth perception fails for objects more than a few tens of meters away. In order to see the shift of an object a city block or more from you, your eyes would need to be spread apart a lot farther.

what would happen if the outer layer of Sun starts falling inward?

outer layer - gas made pf individual atoms, all moving about in random directions--> if layer falls inward, atoms move fasting b/c of falling motion--> if outside fall in = contracts moving atoms closer together = collisions more likely = extra speed of falling motion transferred to other atoms --> increases the speed of atoms-->The temperature of a gas is a measure of the kinetic energy (motion) of the atoms within it; hence, the temperature of this layer of the Sun increases. Collisions also excite electrons within the atoms to higher-energy orbits. When these electrons return to their normal orbits, they emit photons, which can then escape from the Sun

What is a solar month ? What is a sidereal month? Why is one longer than the other?

period of its revolution about Earth measure with respect to the star is little over 27 daysThe time interval in which the phases repeat (full to full) is the solar month(little over 29.5 days)The difference results from Earth's motion around the Sun. The Moon must make more than a complete turnaround the moving Earth to get back to the same phase with respect to the Sun.the Moon changes its position on the celestial sphere rather rapidly: even during a single evening, the Moon creeps visibly eastward among the stars, traveling its own width in a little less than 1 hour. The delay in moonrise from one day to the next caused by this eastward motion averages about 50 minutesThe Moon rotates on its axis in exactly the same time that it takes to revolve about Earth. As a consequence, the Moon always keeps the same face turned toward Earth --> synchronous rotation

describe light as a photon

physicists had to accept that sometimes light behaves more like a "particle"—or at least a self-contained packet of energy—than a wave. We call such a packet of electromagnetic energy a photon

what are evaporating gas globules?

pillars shows some very dense globules, many of which harbor embryonic stars.It is possible that because these EGGs are exposed to the relentless action of the radiation from nearby hot stars, some may not yet have collected enough material to form a star

why do visible-light and infrared telescopes on Earth's surface not produce images as sharp as the theory of light said they should?

planet's atmosphere is turbulentcontains many small-scale blobs or cells of gas that range in size from inches to several feet. Each cell has a slightly different temperature from its neighbor, and each cell acts like a lens, bending (refracting) the path of the light by a small amount. This bending slightly changes the position where each light ray finally reaches the detector in a telescope. The cells of air are in motion, constantly being blown through the light path of the telescope by winds, often in different directions at different altitudes. As a result, the path followed by the light is constantly changing.

what did Hendrik Van de Helst?

predicted that hydrogen would produce a strong line at a wavelength of 21 centimeters. That's quite a long wavelength, implying that the wave has such a low frequency and low energy that it cannot come from electrons jumping between energy levels

what are the solid particles made of ?

primarily composed of elements that are abundant in the universe (and in interstellar matter). After hydrogen and helium, the most abundant elements are oxygen, carbon, and nitrogen. These three elements, along with magnesium, silicon, iron—and perhaps hydrogen itself—turn out to be the most important components of interstellar dust.Many of the dust particles can be characterized as sootlike (rich in carbon) or sandlike (containing silicon and oxygen). Grains of interstellar dust are found in meteorites and can be identified because the abundances of certain isotopes are different from what we see in other solar system material.+ graphite & diamonds

how exactly does the sun tap into energy of nuclei through fusion?

process takes four hydrogen nuclei and fuses them together to form a single helium nucleus. The helium nucleus is slightly less massive than the four hydrogen nuclei that combine to form it, and that mass is converted into energy.

what is the general theory of relativity ?

proposed that gravity was not a mysterious force at all but a result of the geometry of space itselfit helps explain how matter interacts with other matter in space and time.

What are radio waves used for?

radar waves, which are used in radar guns by traffic officers to determine vehicle speeds, AM radio waves, which were the first to be developed for broadcasting.(1m to 100s of meters)With such a wide range of wavelengths, not all radio waves interact with Earth's atmosphere in the same way. FM and TV waves are not absorbed and can travel easily through our atmosphere. AM radio waves are absorbed or reflected by a layer in Earth's atmosphere called the ionosphere

modern determination of solar system dimensions is...

radar, a type of radio wave that can bounce off solid objectsby timing how long a radar beam (traveling at the speed of light) takes to reach another world and return, we can measure the distance involved very accuratelyit is not possible to use radar to measure the distance to the Sun directly because the Sun does not reflect radar very efficiently. But we can measure the distance to many other solar system objects and use Kepler's laws to give us the distance to the Sun.

how to overcome resolution difficulty with radio waves?

radio astronomers have learned to sharpen their images by linking two or more radio telescopes together electronically.

what is the radio astronomy measurement?

radio astronomers measure the amount of energy being collected each second by each square meter of a radio telescope and express the brightness of each source in terms of, for example, watts per square meter.

what does the supernova explosion lead to

recycled by spaceproduces a flood of energetic neutrons that barrel through the expanding material. These neutrons can be absorbed by iron and other nuclei where they can turn into protons. Thus, they can build up elements that are more massive than iron, possibly including such terrestrial favorites as gold, silver and uranium. Supernovae (and, as we will shortly see, the explosive mergers of neutron stars) are the only candidates we have for places where such heavier atoms can be made. Next time you wear some gold jewelry (or give some to your sweetheart), bear in mind that those gold atoms were forged long ago in these kinds of celestial explosions!When supernovae explode, these elements (as well as the ones the star made during more stable times) are ejected into the existing gas between the stars and mixed with it. Thus, supernovae play a crucial role in enriching their galaxy with heavier elements, allowing, among other things, the chemical elements that make up earthlike planets and the building blocks of life to become more common as time goes on

what is the resolution?

refers to the precision of detail present in an image: that is, the smallest features that can be distinguished.--> astronomers want sharpest images

What is the formula for Kepler's third law?

relationship between orbital period of a revolution & its distance from the Sun a 3 = ⎝M 1 + M 2 ⎞ × P 2 Because the mass of planets are so insignificant next to the sun, Kepler did not realize that both masses had to be included in the calculation

what produced these remarkable temperatures in space?

remarkable temperatures is the explosion of massive stars at the ends of their lives (Figure 20.7). Such explosions, called supernovae, will be discussed in detail in the chapter on The Death of Stars. For now, we'll just say that some stars, nearing the ends of their lives, become unstable and literally explode. These explosions launch gas into interstellar space at velocities of tens of thousands of kilometers per second (up to about 30% the speed of light). When this ejected gas collides with interstellar gas, it produces shocks that heat the gas to millions or tens of millions of degrees.

most widely accepted model pictures the interstellar grains

rocky cores that are either like soot (rich in carbon) or like sand (rich in silicates). In the dark clouds where molecules can form, these cores are covered by icy mantles (Figure 20.16). The most common ices in the grains are water (H2O), methane (CH4), and ammonia (NH3)—all built out of atoms that are especially abundant in the realm of the stars. The ice mantles, in turn, are sites for some of the chemical reactions that produce complex organic molecules.FIGURE 20.16

What is a sidereal day?

rotation period of Earth with respect to other stars (astronomers also use this)

what is the remaining 1 percent of stellar material made of ?

s solid—frozen particles consisting of many atoms and molecules that are called interstellar grains or interstellar dust (Figure 20.2). A typical dust grain consists of a core of rocklike material (silicates) or graphite surrounded by a mantle of ices; water, methane, and ammonia are probably the most abundant ices.

what causes our sun to look blue?

scattering of sunlight is also what causes our sky to look blue, even though the gases that make up Earth's atmosphere are transparent. As sunlight comes in, it scatters from the molecules of air. The small size of the molecules means that the blue colors scatter much more efficiently than the greens, yellows, and reds. Thus, the blue in sunlight is scattered out of the beam and all over the sky. The light from the Sun that comes to your eye, on the other hand, is missing some of its blue, so the Sun looks a bit yellower, even when it is high in the sky, than it would from space.

which stars shed enough mass to reach this limit?

search for young clusters that contain one or more white dwarf stars. Remember that more massive stars go through all stages of their evolution more rapidly than less massive ones. Suppose we find a cluster that has a white dwarf member and also contains stars on the main sequence that have 6 times the mass of the Sun. This means that only those stars with masses greater than 6 MSun have had time to exhaust their supply of nuclear energy and complete their evolution to the white dwarf stage. The star that turned into the white dwarf must therefore have had a main-sequence mass of more than 6 MSun, since stars with lower masses have not yet had time to use up their stores of nuclear energy. The star that became the white dwarf must, therefore, have gotten rid of at least 4.6 MSun so that its mass at the time nuclear energy generation ceased could be less than 1.4 MSun.Astronomers continue to search for suitable clusters to make this test, and the evidence so far suggests that stars with masses up to about 8 MSun can shed enough mass to end their lives as white dwarfs. Stars like the Sun will probably lose about 45% of their initial mass and become white dwarfs with masses less than 1.4 MSun.

how to astronomers address the blurriness of images?

search the world for locations where the amount of atmospheric blurring, or turbulence, is as small as possible.best sites are in coastal mountain ranges and on isolated volcanic peaks in the middle of an ocean. Air that has flowed long distances over water before it encounters land is especially stable.

What is the international date line? (what does crossing it west to east mean what about vice versa?)

set by international agreement to run approximately along the 180° meridian of longitude.By convention, at the date line, the date of the calendar is changed by one day. Crossing the date line from west to east, thus advancing your time, you compensate by decreasing the date; crossing from east to west, you increase the date by one day

why was the neutrino so hard to find?

so hard to find is that neutrinos interact very weakly with other matter and therefore are very difficult to detectEarth is more transparent to a neutrino than the thinnest and cleanest pane of glass is to a photon of light. In fact, most neutrinos can pass completely through a star or planet without being absorbed.

how does the Sun's luminosity of 4 * 10^26 watts get produced?

some 600 million tons of hydrogen must be converted into helium each second, of which about 4 million tons are converted from matter into energy. As large as these numbers are, the store of hydrogen (and thus of nuclear energy) in the Sun is still more enormous, and can last a long time—billions of years, in fact.

if particles comes together under strong nuclear force and and form atomic nucleus what happens?

some of the nuclear energy is released. The energy given up in such a process is called the binding energy of the nucleus.

what did 19th century scientist's think produced sun's energy?

source of the Sun's heat might be the mechanical motion of meteorites falling into it--> calculations show in order to produce total energy emitted by Sun, energy emitted by the Sun, the mass in meteorites that would have to fall into the Sun every 100 years would equal the mass of Earth. The resulting increase in the Sun's mass would, according to Kepler's third law, change the period of Earth's orbit by 2 seconds per year. Such a change would be easily measurable and was not, in fact, occurring. Scientists could then disprove this as the source of the Sun's energy.

Why can't we see through the Milky Way Galaxy Rim?

space between stars is taken up by hydrogen gas and solid particles known as interstellar dust

what does reddening mean?

starlight is reddened by interstellar dust means that long-wavelength radiation is transmitted through the Galaxy more efficiently than short-wavelength radiation. Consequently, if we wish to see farther in a direction with considerable interstellar material, we should look at long wavelengths. This simple fact provides one of the motivations for the development of infrared astronomy. In the infrared region at 2 microns (2000 nanometers), for example, the obscuration is only one-sixth as great as in the visible region (500 nanometers), and we can therefore study stars that are more than twice as distant before their light is blocked by interstellar dust. This ability to see farther by observing in the infrared portion of the spectrum represents a major gain for astronomers trying to understand the structure of our Galaxy or probing its puzzling,

which stars can be seen with the naked eye?

stars fainter than the Sun cannot be seen with the unaided eye unless they are very nearby. For example, stars with luminosities ranging from 1/100 to 1/10,000 the luminosity of the Sun (LSun) are very common, but a star with a luminosity of 1/100 LSun would have to be within 5 light-years to be visible to the naked eye—and only three stars (all in one system) are this close to us. The nearest of these three stars, Proxima Centauri, still cannot be seen without a telescope because it has such a low luminosity.

What is star dust?

stars form clusters in which they interact with each; when these stars explode they become star which is the raw material

The primary reason that stellar spectra look different is because

stars have different temperatures.

why two key pieces lead to discovery of Sun's energy?

structure of the nucleus of the atom and the fact that mass can be converted into energy.

what is antimatter?

such antimatter is that when a particle comes into contact with its antiparticle, the original particles are annihilated, and substantial amounts of energy in the form of photons are produced.--> cannot survive very long-->individual antiparticles are found in cosmic rays (particles that arrive at the top of Earth's atmosphere from space) and can be created in particle accelerators.-->is created in the core of the Sun and other stars.

what about the stars 100x more luminous than the sun?

such stars are rare, they are visible to the unaided eye, even when hundreds to thousands of light-years away. A star with a luminosity 10,000 times greater than that of the Sun can be seen without a telescope out to a distance of 5000 light-years. The volume of space included within a distance of 5000 light-years, however, is enormous; so even though highly luminous stars are intrinsically rare, many of them are readily visible to our unaided eye.

how do plot an H-R diagram?

temperature increases toward the left and luminosity toward the top.. The great majority are aligned along a narrow sequence running from the upper left (hot, highly luminous) to the lower right (cool, less luminous). This band of points is called the main sequence.

what does the absence of an element's spectral lines not necessarily mean?

that the element itself is absent. As we saw, the temperature and pressure in a star's atmosphere will determine what types of atoms are able to produce absorption lines. Only if the physical conditions in a star's photosphere are such that lines of an element should (according to calculations) be there can we conclude that the absence of observable spectral lines implies low abundance of the element.If we see lines of iron in a star's spectrum, for example, then we know immediately that the star must contain iron.

The reason the lowest-mass dwarfs are so hard to find is...

that they put out very little light—ten thousand to a million times less light than the Sun. Only recently has our technology progressed to the point that we can detect these dim, cool objects.

One of the most difficult things about precisely measuring the tiny angles of parallax shifts from Earth is....

that you have to observe the stars through our planet's atmosphere

what are solar pulsations?

the Sun pulsates—that is, it alternately expands and contracts—just as your chest expands and contracts as you breathe. This pulsation is very slight, but it can be detected by measuring the radial velocity of the solar surface—the speed with which it moves toward or away from us. The velocities of small regions on the Sun are observed to change in a regular way, first toward Earth, then away, then toward, and so on. It is as if the Sun were "breathing" through thousands of individual lungs, each having a size in the range of 4000 to 15,000 kilometers, each fluctuating back and forth

What is absolute luminosity?

the actual amount of energy radiated from an objectL = 4πR^2σT^4

What is the purpose of the eyepiece?

the additions lens used to view the image formed by the lens in a telescope focuses the image at a distance that is either directly viewable by a human or at a convenient place for a detector. Using different eyepieces, we can change the magnification (or size) of the image and also redirect the light to a more accessible location.

What is apparent brightness?

the amount of a star's energy that reaches a given area (say, one square meter) each second here on Earth.Stars are democratic in how they produce radiation; they emit the same amount of energy in every direction in space.

what happens when a cation meets an anion?

the atom emits one or more photons. Which photons are emitted depends on whether the electron is captured at once to the lowest energy level of the atom or stops at one or more intermediate levels on its way to the lowest available level.

What is precession?

the direction in which Earth's axis points does indeed change slowly but regularly (axis resembles top like motion)--> 26000 years for one circle precession

What is the proton-proton chain?

the chain of fusion reactions, leading from hydrogen to helium, that powers main-sequence stars1H + 1H --> 1H + e^+ + v2H + 1H--> 3He + y3He + 3He --> 4He+ 1H +1H(pg 573)Here, the superscripts indicate the total number of neutrons plus protons in the nucleus, e+ is the positron, v is the neutrino, and γ indicates that gamma rays are emitted. Note that the third step requires two helium-3 nuclei to start; the first two steps must happen twice before the third step can occur.

what can we use spectrometers to measure?

the changing velocity of stars with planets around them.As the star and planet orbit each other, part of their motion will be in our line of sight (toward us or away from us). Such motion can be measured using the Doppler effect and the star's spectrum. As the star moves back and forth in orbit around the system's center of mass in response to the gravitational tug of an orbiting planet, the lines in its spectrum will shift back and forth.

When the collapse of a high-mass star's core is stopped by degenerate neutrons....

the core is saved from further destruction, but it turns out that the rest of the star is literally blown apart.

what is the ground state?

the lowest possible energy of an atom described by quantum mechanics

What is an astronomical unit?

the distances from the Earth-Sun One year ( 3 * 10 ^7 seconds) for earth to go around the sun

what are the wave-like characteristics of light?

the disturbance travels rapidly outward from the point of origin and can use its energy to disturb other things farther away.For example, in water, the expanding ripples moving away from our frog could disturb the peace of a dragonfly resting on a leaf in the same pool.electromagnetic waves: the radiation generated by a transmitting antenna full of charged particles and moving electrons at your local radio station can, sometime later, disturb a group of electrons in your car radio antenna and bring you the news and weather while you are driving to class or work in the morning.

Where is the light we are observing now coming from?

the farther away from an object the longer it takes for the light to get here and the longer ago the object was at its place of origin --> by looking billions of billions of light-years away

Why produces the enormous quasar energy?

the gas is heated to millions of degrees as it falls towards a black hole and swirls around it ( most distant observed beacons of light)

what is the first step of fusion in the Sun?

the high temperatures inside the Sun's core, two protons combine to make a deuterium nucleus, which is an isotope (or version) of hydrogen that contains one proton and one neutron.one of the original protons has been converted into a neutron in the fusion reaction. Electric charge has to be conserved in nuclear reactions, and it is conserved in this one. A positron (antimatter electron) emerges from the reaction and carries away the positive charge originally associated with one of the protons.

what are challenges in observing the universe in the infrared band of the spectrum?

the infrared region extends from wavelengths near 1 micrometer (μm), which is about the long wavelength sensitivity limit of both CCDs and photography, to 100 micrometers or longermain challenge to astronomers using infrared is to distinguish between the tiny amount of heat radiation that reaches Earth from stars and galaxies, and the much greater heat radiated by the telescope itself and our planet's atmosphere.Typical temperatures on Earth's surface are near 300 K, and the atmosphere through which observations are made is only a little cooler. According to Wien's law, the telescope, the observatory, and even the sky are radiating infrared energy with a peak wavelength of about 10 micrometers. The challenge is to detect faint cosmic sources against this sea of infrared light.

What is the law of conservation of energy?

the law that states that energy cannot be created or destroyed but can be changed from one form to another

what happens on the inside of white dwarfs?

the matter inside them behaves in a very unusual way—unlike anything we know from everyday experience. At this high density, gravity is incredibly strong and tries to shrink the star still further, but all the electrons resist being pushed closer together and set up a powerful pressure inside the core. This pressure is the result of the fundamental rules that govern the behavior of electrons

What is angular momentum?

the measure of rotation of an object as it moves around a fixed point v*m*distance from point constant v and constant distance = same momentum as planets get closer to the sun, it speeds up to conserve angular momentum

How many degrees the moon move each day and how long does it take to complete one revolution?

the moon moves 12 degrees each day 24 times its own width

what is the relationship between mass and luminosity?

the more massive a star is, the more luminous it isM^3.9 ~L(deviations from this rule are white dwarf stars) Refer to figure 18.9 --> 90 percent of stars obey this ruleL/LSun =⎝M/MSun)^4

how can small velocity variations be used to determine what the interior of the Sun is like?

the motion of the Sun's surface is caused by waves that reach it from deep in the interior. Study of the amplitude and cycle length of velocity changes provides information about the temperature, density, and composition of the layers through which the waves passed before they reached the surface. The situation is somewhat analogous to the use of seismic waves generated by earthquakes to infer the properties of Earth's interior. For this reason, studies of solar oscillations (back-and-forth motions) are referred to as helioseismology.

What is frequency?

the number of wave cycles that pass by per second.Heinrich Hertz, the physicist who—inspired by Maxwell's work—discovered radio waves, a cps is also called a hertz (Hz).

What is the ecliptic?

the path the Sun appears to trace around the celestial sphere each year

What is a zodiac?

the path which the soon, moon and earth travel on same plane within an 18 degrees belt on the ecliptic called the zodiac

what is the equivalence principle

the principle stating that there is no difference between a frame of reference that is freely floating through space and one that is freely falling within a gravitational fieldno experiment she can perform inside the sealed laboratory to determine whether she is floating in space or falling freely in a gravitational fieldfree fall = zero gravity

What is Aristotle's reasoning for why moon phases happen?

the progression of the Moon's phases—its apparent changing shape—results from our seeing different portions of the Moon's sunlit hemisphere as the month goes by

what happens after a telescope collects radiation from an astronomical source

the radiation must be detected and measured.detectors : eye --> photography

what happens when binding energy is released?

the resulting nucleus has slightly less mass than the sum of the masses of the particles that came together to form it. In other words, the energy comes from the loss of mass. This slight deficit in mass is only a small fraction of the mass of one proton. But because each bit of lost mass can provide a lot of energy (remember, E = mc2), this nuclear energy release can be quite substantial.

The reason massive stars are such spendthrifts is that, as we saw above, the rate of fusion depends very strongly on

the star's core temperature. And what determines how hot a star's central regions get? It is the mass of the star—the weight of the overlying layers determines how high the pressure in the core must be: higher mass requires higher pressure to balance it. Higher pressure, in turn, is produced by higher temperature. The higher the temperature in the central regions, the faster the star races through its storehouse of central hydrogen. Although massive stars have more fuel, they burn it so prodigiously that their lifetimes are much shorter than those of their low-mass counterparts. You can also understand now why the most massive main-sequence stars are also the most luminous. Like new rock stars with their first platinum album, they spend their resources at an astounding rate.

What is astronomy?

the study of objects that lay beyond Earth and the processes through which they interact --> how we make sense of the universe from the BigBang to now

What is space velocity?

the total (three-dimensional) speed and direction with which an object is moving through space relative to the Sunto know sv we must know its radial velocity, proper motion, and distance

what is luminosity?

the total amount of energy at all wavelengths that it emits per second.express the luminosity of other stars in terms of the Sun's luminosity

what are molecular clouds?

the vibration and rotation of atoms within molecules can leave spectral fingerprints in radio and infrared waves.If we spread out the radiation at such longer wavelengths, we can detect emission or absorption lines in the spectra that are characteristic of specific molecules.Over the years, experiments in our laboratories have shown us the exact wavelengths associated with changes in the rotation and vibration of many common molecules, giving us a template of possible lines against which we can now compare our observations of interstellar matter.

what happens when the source of waves moves towards you?

the wavelength decreases a bit. If the waves involved are visible light, then the colors of the light change slightly. As wavelength decreases, they shift toward the blue end of the spectrum: astronomers call this a blueshift (towards the violet end of spectrum)

what is visible light and where are they observed from?

the waves that human vision can perceive.band of the electromagnetic spectrum that most readily reaches Earth's surface.human eyes evolved to see the kinds of waves that arrive from the Sun most effectively

what do strong lines on a spectrum mean of an element?

there are more atoms in the stellar photosphere absorbing light. Therefore, we know immediately that the star with stronger sodium lines contains more sodium

What about the other stars on the H-R diagram—the giants and supergiants, and the white dwarfs?

these are what main-sequence stars turn into as they age: They are the later stages in a star's life. As a star consumes its nuclear fuel, its source of energy changes, as do its chemical composition and interior structure. These changes cause the star to alter its luminosity and surface temperature so that it no longer lies on the main sequence on our diagram. Because stars spend much less time in these later stages of their lives, we see fewer stars in those regions of the H-R diagram.

how does the spectrum of rotation of distant object look like ? how would measure them instead?

they all appear as unresolved points. The best we can do is to analyze the light from the entire star at once. Due to the Doppler effect, the lines in the light that come from the side of the star rotating toward us are shifted to shorter wavelengths and the lines in the light from the opposite edge of the star are shifted to longer wavelengths. You can think of each spectral line that we observe as the sum or composite of spectral lines originating from different speeds with respect to us. Each point on the star has its own Doppler shift, so the absorption line we see from the whole star is actually much wider than it would be if the star were not rotating. If a star is rotating rapidly, there will be a greater spread of Doppler shifts and all its spectral lines should be quite broad. In fact, astronomers call this effect line broadening, and the amount of broadening can tell us the speed at which the star rotates (

why are the rays of light from the same star parallel?

they are extremely far away By the time the few rays of light pointed toward us actually arrive at Earth, they are, for all practical purposes, parallel to each other.

Why do astronauts aboard Space shuttle appear to have no gravitational forces on them?

they are in freefall they are in free fall and accelerate at the same rate as everything around them--> they are falling around Earth as a result they will continue to fall and said to be in orbit around Earth

In order to specify the exact color of a star, astronomers normally measure a star's apparent brightness....

through filters, each of which transmits only the light from a particular narrow band of wavelengths (colors). A crude example of a filter in everyday life is a green-colored, plastic, soft drink bottle, which, when held in front of your eyes, lets only the green colors of light through.

What happens if the Sun and Moon are lined up? What about if they are at 90 degree angles?

tides stronger when they are lined up and weakened at 90 degrees

What is apparent solar time?

time reckoned by the actual position of the Sun in the sky or below the horizon--> represented by sundialsDuring the first half of the day, the Sun has not yet reached the meridian (the great circle in the sky that passes through our zenith). We designate those hours as before midday (ante meridiem, or a.m.), before the Sun reaches the local meridian. We customarily start numbering the hours after noon over again and designate them by p.m. (post meridiem), after the Sun reaches the local meridian

What other reasons can be used explain why earth is round?

time zones, 90 minutes pictures from satellites, hull disappearing but mast being still visible

why do we Measures three or four evenly spaced transits ?

to "discover" an exoplanet. But in a new field like exoplanet research, we would like to find further independent verification. The strongest confirmation happens when ground-based telescopes are also able to detect a Doppler shift with the same period as the transits. However, this is generally not possible for Earth-size planets. One of the most convincing ways to verify that a dip in brightness is due to a planet is to find more planets orbiting the same star—a planetary system. Multi-planet systems also provide alternative ways to estimate the masses of the planets, as we will discuss in the next section.

what is a field?

to describe the action of forces that one object exerts on other distant objects. Sun produces a gravitational field that controls Earth's orbit, even though the Sun and Earth do not come directly into contact. ***we can say that stationary electric charges produce electric fields, and moving electric charges also produce magnetic fields.

what is grating?

to disperse the spectrum.A grating is a piece of material with thousands of grooves on its surface. While it functions completely differently, a grating, like a prism, also spreads light out into a spectrum.

how do we estimate interstellar mass?

total mass = volume × density of atoms × mass per atomV = πR^2 h = cylindrical GalaxyV = (4/3)πR^3= spherical objects

What are the Magellanic Clouds?

two small irregular dwarf galaxies that are found in the South Celestial Hemisphere; in local group and orbiting the Milky Way Galaxy All three of these small galaxies are satellites of the Milky Way Galaxy, interacting with it through the force of gravity

what are binary stars?

two stars that orbit each other, bound together by gravity. Masses of binary stars can be calculated from measurements of their orbits, just as the mass of the Sun can be derived by measuring the orbits of the planets around it

One commonly used set of filters in astronomy measures stellar brightness at three wavelengths corresponding with

ultraviolet, blue, and yellow light. The filters are named: U (ultraviolet), B (blue), and V (visual, for yellow). These filters transmit light near the wavelengths of 360 nanometers (nm), 420 nm, and 540 nm, respectively. The brightness measured through each filter is usually expressed in magnitudes

how mass to energy conversion cause sun to radiate energy?

un could be produced by the complete conversion of about 4 million tons of matter into energy inside the Sun each second. Destroying 4 million tons per second sounds like a lot when compared to earthly things, but bear in mind that the Sun is a very big reservoir of matter. In fact, we will see that the Sun contains more than enough mass to destroy such huge amounts of matter and still continue shining at its present rate for billions of years.

What is dark matter? (model or hypothesis & why?)

uncharacterized intergalactic material it is a model

What are microwaves?

used in short-wave communication and microwave ovens. (1mm to 1 meter)

what is the purpose of radar waves?

used to determine the distances to planets and how fast things are moving in the solar systemhave determined the rotation periods of Venus and Mercury, probed tiny Earth-approaching asteroids, and allowed us to investigate the mountains and valleys on the surfaces of Mercury, Venus, Mars, and the large moons of Jupiter.

what did Hubble use Cepheids to prove?

using cepheids, when he observed them in nearby galaxies and discovered the expansion of the universe.

why is measuring distance to stars difficult?

variety of intrinsic luminosities apparent brightness --> we can calculate how far it is

what is radial velocity?

velocity along the line of sight toward or away from the observer

what happens when the source of waves moves away from you?

wavelength gets longer, we call the change in colors a redshift

what more can we learn from a stars spectrum?

we can detect pressure differences in stars from the details of the spectrum. This knowledge is very useful because giant stars are larger (and have lower pressures) than main-sequence stars, and supergiants are still larger than giants. If we look in detail at the spectrum of a star, we can determine whether it is a main-sequence star, a giant, or a supergiant.

Why can't we see many distant stars? (what does the dust do?)

we cannot see many distant stars because the dust block the little light that they emit, but some can penetrate the smog

what are exoplanetary systems?

we don't expect to find only one planet per star. Our solar system has eight major planets, half a dozen dwarf planets, and millions of smaller objects orbiting the Sun. The evidence we have of planetary systems in formation also suggest that they are likely to produce multi-planet systems.

what can we measure about planets with known densities?

we have been able to measure both the size of the planet from transit data and its mass from Doppler data, yielding an estimate of its density

To estimate the number of Earth-size planets in our Galaxy,

we need to remember that there are approximately 100 billion stars of spectral types F, G, and K. Therefore, we estimate that there are about 30 billion Earth-size planets in our Galaxy. If we include the super-Earths too, then there could be one hundred billion in the whole Galaxy. This idea—that planets of roughly Earth's size are so numerous—is surely one of the most important discoveries of modern astronomy.

what do we know about extremes of stellar luminosities, diameters & densities?

we saw that the most massive main-sequence stars are the most luminous ones. We know of a few extreme stars that are a million times more luminous than the Sun, with masses that exceed 100 times the Sun's mass. These superluminous stars, which are at the upper left of the H-R diagram, are exceedingly hot, very blue stars of spectral type O. These are the stars that would be the most conspicuous at vast distances in space.The cool supergiants in the upper corner of the H-R diagram are as much as 10,000 times as luminous as the Sun. In addition, these stars have diameters very much larger than that of the Sun. As discussed above, some supergiants are so large that if the solar system could be centered in one, the star's surface would lie beyond the orbit of Mars (see Figure 18.16). We will have to ask, in coming chapters, what process can make a star swell up to such an enormous size, and how long these "swollen" stars can last in their distended state.In contrast, the very common red, cool, low-luminosity stars at the lower end of the main sequence are much smaller and more compact than the Sun. An example of such a red dwarf is Ross 614B, with a surface temperature of 2700 K and only 1/2000 of the Sun's luminosity. We call such a star a dwarf because its diameter is only 1/10 that of the Sun. A star with such a low luminosity also has a low mass (about 1/12 that of the Sun). This combination of mass and diameter means that it is so compressed that the star has an average density about 80 times that of the Sun. Its density must be higher, in fact, than that of any known solid found on the surface of Earth. (Despite this, the star is made of gas throughout because its center is so hot.)The faint, red, main-sequence stars are not the stars of the most extreme densities, however. The white dwarfs, at the lower-left corner of the H-R diagram, have densities many times greater still.

selection effect

where our technique of discovery selects certain kinds of objects as "easy finds." As an example of a selection effect in everyday life, imagine you decide you are ready for a new romantic relationship in your life. To begin with, you only attend social events on campus, all of which require a student ID to get in. Your selection of possible partners will then be limited to students at your college. That may not give you as diverse a group to choose from as you want. In the same way, when we first used the Doppler technique, it selected massive planets close to their stars as the most likely discoveries. As we spend longer times watching target stars and as our ability to measure smaller Doppler shifts improves, this technique can reveal more distant and less massive planets too

describe the emission nebulae in the constellation of Sagittarius

where we see an H II region surrounded by a blue reflection nebula. Which type of nebula appears brighter depends on the kinds of stars that cause the gas and dust to glow. Stars cooler than about 25,000 K have so little ultraviolet radiation of wavelengths shorter than 91.2 nanometers—which is the wavelength required to ionize hydrogen—that the reflection nebulae around such stars outshine the emission nebulae. Stars hotter than 25,000 K emit enough ultraviolet energy that the emission nebulae produced around them generally outshine the reflection nebulae.

Since hydrogen is the main constituent of interstellar gas, we often characterize a region of space according to

whether its hydrogen is neutral or ionized.

Comparing the average density of exoplanets to the density of planets in our solar system helps us understand...

whether they are rocky or gaseous in nature. This has been particularly important for understanding the structure of the new categories of super-Earths and mini-Neptunes with masses between 3-10 times the mass of Earth. A key observation so far is that planets that are more than 10 times the mass of Earth have substantial gaseous envelopes (like Uranus and Neptune) whereas lower-mass planets are predominately rocky in nature (like the terrestrial planets).

describe the spectra of ultra cool brown dwarfs

with temperatures of 500-600 K. These objects exhibited absorption lines due to ammonia (NH3), which are not seen in T dwarfs. A new spectral class, Y, was created for these objects. As of 2015, over two dozen brown dwarfs belonging to spectral class Y have been discovered, some with temperatures comparable to that of the human body (about 300 K).Figure 17.8

what happens if you try to cool a telescope within the atmosphere?

would quickly become coated with condensing water vapor and other gases, making it useless. Only in the vacuum of space can optical elements be cooled to hundreds of degrees below freezing and still remain operational.

what does direct imaging work best for?

young gas giant planets that emit infrared light and reside at large separations from their host stars. Young giant planets emit more infrared light because they have more internal energy, stored from the process of planet formation. Even then, clever techniques must be employed to subtract out the light from the host star. In 2008, three such young planets were discovered orbiting HR 8799, a star in the constellation of Pegasus (Figure 21.21). Two years later, a fourth planet was detected closer to the star. Additional planets may reside even closer to HR 8799, but if they exist, they are currently lost in the glare of the star.Since then, a number of planets around other stars have been found using direct imaging. However, one challenge is to tell whether the objects we are seeing are indeed planets or if they are brown dwarfs (failed stars) in orbit around a star.

what is the formula for doppler shift of light?

λ is the wavelength emitted by the source, Δλ is the difference between λ and the wavelength measured by the observer, c is the speed of light, and v is the relative speed of the observer and the source in the line of sight. The variable v is counted as positive if the velocity is one of recession, and negative if it is one of approach. Solving this equation for the velocity, we find v = c × Δλ/λ.

what is a brown dwarf?

"Failed" star; Star not massive enough to sustain nuclear fusion.-->masses intermediate between stars and planetsvery difficult to observe because they are extremely faint and cool, and they put out most of their light in the infrared part of the spectrum. It was only after the construction of very large telescopes, like the Keck telescopes in Hawaii, and the development of very sensitive infrared detectors, that the search for brown dwarfs succeeded.

What is a model?

A hypothesis becomes a model after some testing has been done and it appears to be a valid observation.

What are Fraunhofer lines? What do they tell us about space composition?

Fraunhofer lines are the absorption spectrum of the outer solar atmosphere viewed against the continuous spectrum of the Sun. other scientists succeeded in identifying some of the lines in stellar spectra as those of known elements on Earth, showing that the same chemical elements found in the Sun and planets exist in the stars

What is a total solar eclipse?

If moon is somewhat nearer and moon completely covers Sun = total solar eclipse total eclipse of the Sun occurs at those times when the umbra of the Moon's shadow reaches the surface of Earth

What happens in September and March when there is no direct sunshine?

In September and March, Earth leans "sideways"—neither into the Sun nor away from it—so the two hemispheres are equally favored with sunshine.

How to use triangulation?

The parallax is also the angle that lines AC and BC make—in mathematical terms, the angle subtended by the baseline. A knowledge of the angles at A and B and the length of the baseline, AB, allows the triangle ABC to be solved for any of its dimensions—say, the distance AC or BC. The solution could be reached by constructing a scale drawing or by using trigonometry to make a numerical calculation. If the tree were farther away, the whole triangle would be longer and skinnier, and the parallax angle would be smaller.Thus, we have the general rule that the smaller the parallax, the more distant the object we are measuring must be

what is the period luminosity relation?

The relation that describes how the luminosity of a Cepheid variable star is related to the period between peaks in its brightness; the longer the period, the more luminous the star.--> discovered by Henrietta LeavittLeavitt discovered hundreds of variable stars in the Large Magellanic Cloud and Small Magellanic Cloud, two great star systems that are actually neighboring galaxies (although they were not known to be galaxies then). A small fraction of these variables were cepheids

what happens with the binary system: one white dwarf & other

Under the right circumstances, stars can exchange material, especially during the stages when one of them swells up into a giant or supergiant, or has a strong wind. When this happens and the companion stars are sufficiently close, material can flow from one star to another, decreasing the mass of the donor and increasing the mass of the recipient. Such mass transfer can be especially dramatic when the recipient is a stellar remnant such as a white dwarf or a neutron star.

what are conclusions from the Rutherford experiment?

Was that nearly all of the mass as well as all of the positive charge in each individual good atom is concentrated in the nucleus- Rutherfords model placed electrons in orbit around this nucleus- his model requires that the electrons be in motion because if stationary they would fall into each otherBecause electrons and nucleus are extremely small, most of the atom is empty

so are white dwarfs degenerate stars?

White dwarfs, then, are stable, compact objects with electron-degenerate cores that cannot contract any further. Calculations showing that white dwarfs are the likely end state of low-mass starsSubrahmanyan Chandrasekhar. He was able to show how much a star will shrink before the degenerate electrons halt its further contraction and hence what its final diameter will be

how did Wollaston improve the spectrometer?

William Wollaston built an improved spectrometer that included a lens to focus the Sun's spectrum on a screen. With this device, Wollaston saw that the colors were not spread out uniformly, but instead, some ranges of color were missing, appearing as dark bands in the solar spectrum. He mistakenly attributed these lines to natural boundaries between the colors.. In 1815, German physicist Joseph Fraunhofer, upon a more careful examination of the solar spectrum, found about 600 such dark lines (missing colors), which led scientists to rule out the boundary hypothesis

What is a quasar?

a bright center of a galaxy that is light by a unique energy process

Is astronomy an observational or historical science?

both we view objects and see how they vary from each other to make scientific observations (subject to change) we observe what has already happened

what is the selection effect

contrast between stars that are close to us and those that can be seen with the unaided eyeWhen a population of objects (stars in this example) includes a great variety of different types, we must be careful what conclusions we draw from an examination of any particular subgroup (this one is heavily weighted to most luminous stars)t requires much more effort to assemble a complete data set for the nearest stars, since most are so faint that they can be observed only with a telescope. However, it is only by doing so that astronomers are able to know about the properties of the vast majority of the stars, which are actually much smaller and fainter than our own SUn

what is dispersion?

different wavelengths (or colors of light) are bent by different amounts and therefore follow slightly different paths through the prism. The violet light is bent more than the red.

what is the interstellar material (ISM)

the gas and dust in the interstellar space between a galaxy's stars the entire collection of interstellar matter

Why do we strive for telescopes that observe fainter light?

they can observe fainter objects

In a transit, the planet's circular disk blocks the light of the star's circular disk. The area of a circle is πR2. The amount of light the planet blocks, called the transit depth, is then given by

πR^2planet/πR^2star= R^2 planet/ R^2 star

what are radio waves used for in space?

--> cannot be heard--> if translated to sound = static-->information that can tell us about the chemistry and physical conditions of the sources of the waves.-->world's largest radio reflectors that can be pointed to any direction in the sky have apertures of 100 meter

What did Galileo's see with his telescope and what theory did he confirm?

--> saw moons on other planets so earth must have a moon --> saw craters on the moon

What are Tacho Brahe's contributions?

-observed exploding stars in the brilliance of the space -erected an observatory -saw a discrepancy between the observations of Ptolemy and actual locations of planets

with adaptive optics, ground-based telescopes can achieve resolutions of.....

0.1 arcsecond or a little better in the infrared region of the spectrum. This impressive figure is the equivalent of the resolution that the Hubble Space Telescope achieves in the visible-light region of the spectrum.

the smallest mass that a true star can have is....

1/12 that of the Sun. By a "true" star, astronomers mean one that becomes hot enough to fuse protons to form heliumObjects with masses between roughly 1/100 and 1/12 that of the Sun may produce energy for a brief time by means of nuclear reactions involving deuterium, but they do not become hot enough to fuse protons. Such objects are intermediate in mass between stars and planets and have been given the name brown dwarfs

The ecliptic is angled at

23.5 degrees

What was Copernicus' theory?

> new sun centered, heliocentric model of the solar systemDe Revolutionibus Orbium Coelestium (On the Revolution of Celestial Orbs), published in 1543, the year of his death. --> develop an improved theory from which to calculate planetary positions, but in doing so, he was himself not free of all traditional prejudices --> proved the circular orbit and defense of heliocentrism with evidenceBiggest reservation was that if earth was moving we would feel it --> however we have seen trees move while we are the ones that are movingHe also reasoned that the apparent rotation of the celestial sphere could be explained by assuming that Earth rotates while the celestial sphere is stationary

What were Galileo's contributions to the field of mechanics?

> rest is no more natural than motionreasoned that if all resisting effects could be removed the object would remain in steady motion indefinitelyhe argued that forces not only needed to start motion but also to stop itAccelerate: change in speed or direction--> objects accelerate uniformly in equal intervals of time they gain equal increments of speedDefended Copernicus heliocentric theor

what is the H 11 region?

A cloud of ionized hydrogen Scientists who work with spectra use the Roman numeral I to indicate that an atom is neutral; successively higher Roman numerals are used for each higher stage of ionization. H II thus refers to hydrogen that has lost its one electron; Fe III is iron with two electrons missing

What is the Local Group?

A cluster of about 30 galaxies of which the Milky Way is a member.

what is the cepheid light curve?

A graph that shows how the brightness of a variable star changes with time is called a light curve (Figure 19.9). The maximum is the point of the light curve where the star has its greatest brightness; the minimum is the point where it is faintest. If the light variations repeat themselves periodically, the interval between the two maxima is called the period of the star.

What is a hypothesis? (what makes something a better hypothesis than something else?)

A hypothesis in a plausible explanation that can be tested --> more experiments that substantiate a hypothesis the greater the the validity and likelihood it will be in the the nature of observation

What are the Balmer series

A set of spectral lines that appear in the visible light region when a hydrogen atom undergoes a transition from energy levels n>2 to n=2.

How does a total eclipse look like?

A solar eclipse starts when the Moon just begins to silhouette itself against the edge of the Sun's disk. A partial phase follows, during which more and more of the Sun is covered by the Moon. About an hour after the eclipse begins, the Sun becomes completely hidden behind the Moon.During totality, the sky is dark enough that planets become visible in the sky, and usually the brighter stars do as well.The corona is the Sun's outer atmosphere, consisting of sparse gases that extend for millions of miles in all directions from the apparent surface of the Sun.Only when the brilliant glare from the Sun's visible disk is blotted out by the Moon during a total eclipse is the pearly white corona visible

What is the axis of rotation?

An imaginary line running through the center of the Earth that Earth spins around

how to determine whether a specific object is a brown dwarf or a very low mass star?

An independent measure of mass is required to determine whether a specific object is a brown dwarf or a very low mass star. Since brown dwarfs cool steadily throughout their lifetimes, the spectral type of a given brown dwarf changes with time over a billion years or more from late M through L, T, and Y spectral types.

doppler effect and motion

An observed change in the frequency of a wave when the source or observer is movingThe greater the motion toward or away from us, the greater the Doppler shift. V/c formula

how do the electrons act as the star dies

As the star's core contracts, electrons are squeezed closer and closer together. Eventually, a star like the Sun becomes so dense that further contraction would in fact require two or more electrons to violate the rule against occupying the same place and moving in the same way.Such a dense gas is said to be degenerate

But if all the stars on the main sequence are doing the same thing (fusing hydrogen), why are they distributed along a sequence of points? That is, why do they differ in luminosity and surface temperature (which is what we are plotting on the H-R diagram)?

Astrophysicists have been able to show that the structure of stars that are in equilibrium and derive all their energy from nuclear fusion is completely and uniquely determined by just two quantities: the total mass and the composition of the star. This fact provides an interpretation of many features of the H-R diagram.Imagine a cluster of stars forming from a cloud of interstellar "raw material" whose chemical composition is similar to the Sun's.In such a cloud, all the clumps of gas and dust that become stars begin with the same chemical composition and differ from one another only in mass. Now suppose that we compute a model of each of these stars for the time at which it becomes stable and derives its energy from nuclear reactions, but before it has time to alter its composition appreciably as a result of these reactions.The models calculated for these stars allow us to determine their luminosities, temperatures, and sizes. If we plot the results from the models—one point for each model star—on the H-R diagram, we get something that looks just like the main sequence we saw for real stars.

how to get mass of each star from mass of both binary stars

But the relative orbital speeds of the two stars can tell us how much of the total mass each star has. As we saw in our seesaw analogy, the more massive star is closer to the center of mass and therefore has a smaller orbit. Therefore, it moves more slowly to get around in the same time compared to the more distant, lower-mass star. If we sort out the speeds relative to each other, we can sort out the masses relative to each other

what do color indicate about stars?

Color does not depend on the distance to the object.Blue colors dominate the visible light output of very hot stars (with much additional radiation in the ultraviolet). On the other hand, cool stars emit most of their visible light energy at red wavelengths (with more radiation coming off in the infrared)

What was copernicus able to explain with this new model?

Copernicus worked on a general model with sun in the middle and deduced that planets closer to the Sun have greater orbital speeds--> could explain retrograde motions w/o epicycles

what is the difference between the density of a molecular cloud core and the density of the youngest stars that can be detected?

Direct observations of this collapse to higher density are nearly impossible for two reasons. First, the dust-shrouded interiors of molecular clouds where stellar births take place cannot be observed with visible light. Second, the timescale for the initial collapse—thousands of years—is very short, astronomically speaking. Since each star spends such a tiny fraction of its life in this stage, relatively few stars are going through the collapse process at any given time. Nevertheless, through a combination of theoretical calculations and the limited observations available, astronomers have pieced together a picture of what the earliest stages of stellar evolution are likely to be.

how does the lighting curve of an eclipsing binary look?

During the time interval between the first and second contacts, the smaller star has moved a distance equal to its own diameter. During the time interval from the first to third contacts, the smaller star has moved a distance equal to the diameter of the larger star. If the spectral lines of both stars are visible in the spectrum of the binary, then the speed of the smaller star with respect to the larger one can be measured from the Doppler shift. But knowing the speed with which the smaller star is moving and how long it took to cover some distance can tell the span of that distance—in this case, the diameters of the stars. The speed multiplied by the time interval from the first to second contact gives the diameter of the smaller star. We multiply the speed by the time between the first and third contacts to get the diameter of the larger star.**: orbits are generally not seen exactly edge-on, and the light from each star may be only partially blocked by the other. Furthermore, binary star orbits, just like the orbits of the planets, are ellipses, not circles. However, all these effects can be sorted out from very careful measurements of the light curve.

how does low pressure affect spectrum of giant?

First, a star with a lower-pressure photosphere shows narrower spectral lines than a star of the same temperature with a higher-pressure photosphere (Figure 17.9). The difference is large enough that careful study of spectra can tell which of two stars at the same temperature has a higher pressure (and is thus more compressed) and which has a lower pressure (and thus must be extended). This effect is due to collisions between particles in the star's photosphere—more collisions lead to broader spectral lines. Collisions will, of course, be more frequent in a higher-density environment. Think about it like traffic—collisions are much more likely during rush hour, when the density of cars is high.Second, more atoms are ionized in a giant star than in a star like the Sun with the same temperature. The ionization of atoms in a star's outer layers is caused mainly by photons, and the amount of energy carried by photons is determined by temperature. But how long atoms stay ionized depends in part on pressure. Compared with what happens in the Sun (with its relatively dense photosphere), ionized atoms in a giant star's photosphere are less likely to pass close enough to electrons to interact and combine with one or more of them, thereby becoming neutral again. Ionized atoms, as we discussed earlier, have different spectra from atoms that are neutral.

What did Hipparchus discover about Earth's axis

H erected an observatory on the island of Rhodes around 150 BCE when Romans expanded into MediterraneanPioneering star catalog with about 850 entries with their specific location in the sky (like longitude and latitude)Divided the stars into apparent magnitudes according to apparent brightness--> first magnitude (brightest), second magnitude.......etc. Made discovery: the position in the sky of the north celestial pole had altered over the previous century and a half--> direction around which the sky appears to rotate changes slowly but continuously

what is the doppler effect on stars?

If a star approaches or recedes from us, the wavelengths of light in its continuous spectrum appear shortened or lengthened, respectively, as do those of the dark lines. However, unless its speed is tens of thousands of kilometers per second, the star does not appear noticeably bluer or redder than normal. The Doppler shift is thus not easily detected in a continuous spectrum and cannot be measured accurately in such a spectrum. The wavelengths of the absorption lines can be measured accurately, however, and their Doppler shift is relatively simple to detect.

Ionization

If enough energy is absorbed, the electron can be completely removed from the atom

how does the sun maintain its stability?

If the internal pressure in such a star were not great enough to balance the weight of its outer parts, the star would collapse somewhat, contracting and building up the pressure inside. On the other hand, if the pressure were greater than the weight of the overlying layers, the star would expand, thus decreasing the internal pressure. Expansion would stop, and equilibrium would again be reached when the pressure at every internal point equaled the weight of the stellar layers above that point.***hydrostatic equilibrium

What is moon and sky had the same path?

If the path of the Moon in the sky were identical to the path of the Sun (the ecliptic), we might expect to see an eclipse of the Sun and the Moon each month—whenever the Moon got in front of the Sun or into the shadow of Earth. However, as we mentioned, the Moon's orbit is tilted relative to the plane of Earth's orbit about the Sun by about 5° (imagine two hula hoops with a common center, but tilted a bit).As a result, during most months, the Moon is sufficiently above or below the ecliptic plane to avoid an eclipse. But when the two paths cross (twice a year), it is then "eclipse season" and eclipses are possible.

how does the The Doppler method allows us to estimate the mass of a planet?

If the same object can be studied by both the Doppler and transit techniques, we can measure both the mass and the size of the exoplanet. This is a powerful combination that can be used to derive the average density (mass/volume) of the planet. In 1999, using measurements from ground-based telescopes, the first transiting planet was detected orbiting the star HD 209458. The planet transits its parent star for about 3 hours every 3.5 days as we view it from Earth. Doppler measurements showed that the planet around HD 209458 has about 70% the mass of Jupiter, but its radius is about 35% larger than Jupiter's. This was the first case where we could determine what an exoplanet was made of—with that mass and radius, HD 209458 must be a gas and liquid world like Jupiter or Saturn.

where do molecules come from?

It is in these dark regions of space, protected from starlight, that molecules can form. Chemical reactions occurring both in the gas and on the surface of dust grains lead to much more complex compounds, hundreds of which have been identified in interstellar space. Among the simplest of these are water (H2O), carbon monoxide (CO), which is produced by fires on Earth, and ammonia (NH3), whose smell you recognize in strong home cleaning products. Carbon monoxide is particularly abundant in interstellar space and is the primary tool that astronomers use to study giant molecular clouds. Unfortunately, the most abundant molecule, H2, is particularly difficult to observe directly because in most giant molecular clouds, it is too cold to emit even at radio wavelengths. CO, which tends to be present wherever H2 is found, is a much better emitter and is often used by astronomers to trace molecular hydrogen

how do we know its a spectroscopic binary if it doesn't show two spectral lines?

Nevertheless, the periodic shifting back and forth of the brighter star's lines gave evidence that it was revolving about an unseen companion. (The lines of both components need not be visible for a star to be recognized as a spectroscopic binary.)

why is it that even at high temps, it is difficult to force two protons to combine?

On average, a proton will rebound from other protons in the Sun's crowded core for about 14 billion years, at the rate of 100 million collisions per second, before it fuses with a second proton. This is, however, only the average waiting time. Some of the enormous numbers of protons in the Sun's inner region are "lucky" and take only a few collisions to achieve a fusion reaction: they are the protons responsible for producing the energy radiated by the Sun. Since the Sun is about 4.5 billion years old, most of its protons have not yet been involved in fusion reactions.

what is a Herbig-Haro (HH) object?

On occasion, the jets of high-speed particles streaming away from the protostar collide with a somewhat-denser lump of gas nearby, excite its atoms, and cause them to emit light. These glowing regions, each of which is known as a Herbig-Haro (HH) object after the two astronomers who first identified them, allow us to trace the progress of the jet to a distance of a light-year or more from the star that produced it.

how did castor prove binary stars existence?

One well-known binary star is Castor, located in the constellation of Gemini. By 1804, astronomer William Herschel, who also discovered the planet Uranus, had noted that the fainter component of Castor had slightly changed its position relative to the brighter component. (We use the term "component" to mean a member of a star system.) Here was evidence that one star was moving around another. It was actually the first evidence that gravitational influences exist outside the solar system.

Just how different are these red giants and supergiants from a main-sequence star?

Relative to the Sun, this supergiant has a much larger radius, a much lower average density, a cooler surface, and a much hotter core.Table 22.2Red giants can become so large that if we were to replace the Sun with one of them, its outer atmosphere would extend to the orbit of Mars or even beyond (Figure 22.4). This is the next stage in the life of a star as it moves (to continue our analogy to human lives) from its long period of "youth" and "adulthood" to "old age." (After all, many human beings today also see their outer layers expand a bit as they get older.) By considering the relative ages of the Sun and Betelgeuse, we can also see that the idea that "bigger stars die faster" is indeed true here. Betelgeuse is a mere 10 million years old, which is relatively young compared with our Sun's 4.5 billion years, but it is already nearing its death throes as a red supergiant.

colors vs spectral classes to estimate the temperature of a star: which one would you use and why?

Spectra are harder to measure because the light has to be bright enough to be spread out into all colors of the rainbow, and detectors must be sensitive enough to respond to individual wavelengths. In order to measure colors, the detectors need only respond to the many wavelengths that pass simultaneously through the colored filters that have been chosen—that is, to all the blue light or all the yellow-green light.

what is the source of many of the high-energy cosmic ray particles?

SupernovaeTrapped by the magnetic field of the Galaxy, the particles from exploded stars continue to circulate around the vast spiral of the Milky Way. Scientists speculate that high-speed cosmic rays hitting the genetic material of Earth organisms over billions of years may have contributed to the steady mutations—subtle changes in the genetic code—that drive the evolution of life on our planet.

what is direct detection?

Suppose, for example, you were a great distance away and wished to detect reflected light from Earth. Earth intercepts and reflects less than one billionth of the Sun's radiation, so its apparent brightness in visible light is less than one billionth that of the Sun. Compounding the challenge of detecting such a faint speck of light, the planet is swamped by the blaze of radiation from its parent star.Even today, the best telescope mirrors' optics have slight imperfections that prevent the star's light from coming into focus in a completely sharp point

What is the celestial sphere?

The celestial sphere is a representation of how the entire sky looks as seen from Earth.

where does the energy of the inward falling material is converted to heat flow?

The heat generated in this way, like all heat, flows outward to where it is a bit cooler. In the process, the heat raises the temperature of a layer of hydrogen that spent the whole long main-sequence time just outside the core. Like an understudy waiting in the wings of a hit Broadway show for a chance at fame and glory, this hydrogen was almost (but not quite) hot enough to undergo fusion and take part in the main action that sustains the star. Now, the additional heat produced by the shrinking core puts this hydrogen "over the limit," and a shell of hydrogen nuclei just outside the core becomes hot enough for hydrogen fusion to begin.New energy produced by fusion of this hydrogen now pours outward from this shell and begins to heat up layers of the star farther out, causing them to expand. Meanwhile, the helium core continues to contract, producing more heat right around it. This leads to more fusion in the shell of fresh hydrogen outside the core (Figure 22.2). The additional fusion produces still more energy, which also flows out into the upper layer of the star

what is the relationship between magnitude and brightness?

The important fact to remember when using magnitude is that the system goes backward: the larger the magnitude, the fainter the object you are observing.

What are fullerenes?

The largest compounds yet discovered in interstellar space are fullerenes, molecules in which 60 or 70 carbon atoms are arranged in a cage-like configuration

what is the chandrashekar limit?

The maximum mass that a star can end its life with and still become a white dwarf—1.4 MSun—is called the Chandrasekhar limit. Stars with end-of-life masses that exceed this limit have a different kind of end in store

what is the doppler method of detecting planets?

The motion of a star around a common center of mass with an orbiting planet can be detected by measuring the changing speed of the star. When the star is moving away from us, the lines in its spectrum show a tiny redshift; when it is moving toward us, they show a tiny blueshift. The change in color (wavelength) has been exaggerated here for illustrative purposes. In reality, the Doppler shifts we measure are extremely small and require sophisticated equipment to be detected.

What is radiation?

The transfer of energy by electromagnetic waves

what does the radial velocity curve show

These curves plot the radial velocities of two stars in a spectroscopic binary system, showing how the stars alternately approach and recede from Earth. Note that positive velocity means the star is moving away from us relative to the center of mass of the system, which in this case is 40 kilometers per second. Negative velocity means the star is moving toward us relative to the center of mass.

where there only certain lines on spectra?

These gases turned out not to be transparent at all colors: they were quite opaque at a few sharply defined wavelengths. Something in each gas had to be absorbing just a few colors of light and no others.clear that certain lines in the spectrum "go with" certain elements

What did Hipparchus discover about stars and apparent magnitude?

This indicated that the Sun was directly over the well—meaning that Syene was on a direct line from the center of Earth to the Sun. At the corresponding time and date in Alexandria, Eratosthenes observed the shadow a column made and saw that the Sun was not directly overhead, but was slightly south of the zenith, so that its rays made an angle with the vertical equal to about 1/50 of a circle (7°).Because the Sun's rays striking the two cities are parallel to one another, why would the two rays not make the same angle with Earth's surface?Shadow of a column--> 7 degrees because of curvature--> Alexandria must be 1/50 Earth's circumference north of Syene --> Alexandria was 5000 stadia north of Syene--> 50 * 5000= 250000 stadia-> accuracy undeterminable because stadia measurement

How did Eratosthenes prove Earth's curvature?

This indicated that the Sun was directly over the well—meaning that Syene was on a direct line from the center of Earth to the Sun. At the corresponding time and date in Alexandria, Eratosthenes observed the shadow a column made and saw that the Sun was not directly overhead, but was slightly south of the zenith, so that its rays made an angle with the vertical equal to about 1/50 of a circle (7°).Because the Sun's rays striking the two cities are parallel to one another, why would the two rays not make the same angle with Earth's surface?Shadow of a column--> 7 degrees because of curvature--> Alexandria must be 1/50 Earth's circumference north of Syene --> Alexandria was 5000 stadia north of Syene--> 50 * 5000= 250000 stadia-> accuracy undeterminable because stadia measurement unknown

What is a neutron star?

This means the collapsing core can reach a stable state as a crushed ball made mainly of neutrons, which astronomers call a neutron star. We don't have an exact number (a "Chandrasekhar limit") for the maximum mass of a neutron star, but calculations tell us that the upper mass limit of a body made of neutrons might only be about 3 MSun. So if the mass of the core were greater than this, then even neutron degeneracy would not be able to stop the core from collapsing further. The dying star must end up as something even more extremely compressed, which until recently was believed to be only one possible type of object—the state of ultimate compaction known as a black hole (which is the subject of our next chapter). This is because no force was believed to exist that could stop a collapse beyond the neutron star stage.

how do binary stars affect each other's evolution?

Under the right circumstances, stars can exchange material, especially during the stages when one of them swells up into a giant or supergiant, or has a strong wind. When this happens and the companion stars are sufficiently close, material can flow from one star to another, decreasing the mass of the donor and increasing the mass of the recipient. Such mass transfer can be especially dramatic when the recipient is a stellar remnant such as a white dwarf or a neutron star.

whats the problem with airborne & space infrared telescopes?

Water vapor, the main source of atmospheric interference for making infrared observations, is concentrated in the lower part of Earth's atmosphere.--> need to go to space or on a plane to avoid this

why do we see doppler shifts in stars?

We see changes in velocity because when one star is moving toward Earth, the other is moving away; half a cycle later, the situation is reversed. Doppler shifts cause the spectral lines to move back and forth. In diagrams 1 and 3, lines from both stars can be seen well separated from each other. When the two stars are moving perpendicular to our line of sight (that is, they are not moving either toward or away from us), the two lines are exactly superimposed, and so in diagrams 2 and 4, we see only a single spectral line. Note that in the diagrams, the orbit of the star pair is tipped slightly with respect to the viewer (or if the viewer were looking at it in the sky, the orbit would be tilted with respect to the viewer's line of sight). If the orbit were exactly in the plane of the page or screen (or the sky), then it would look nearly circular, but we would see no change in radial velocity (no part of the motion would be toward us or away from us.) If the orbit were perpendicular to the plane of the page or screen, then the stars would appear to move back and forth in a straight line, and we would see the largest-possible radial velocity variations.

What is an H-R diagram?

a graph that shows the relationship between a star's surface temperature and absolute magnitude

Once a star has reached the main-sequence stage of its life, it derives its energy...

almost entirely from the conversion of hydrogen to helium via the process of nuclear fusion in its coreSince hydrogen is the most abundant element in stars, this process can maintain the star's equilibrium for a long time. Thus, all stars remain on the main sequence for most of their lives. Some astronomers like to call the main-sequence phase the star's "prolonged adolescence" or "adulthood"

before the light reaches the detector, astronomers use some type of

an instrument to sort the light according to wavelength. The instrument may be as simple as colored filters, which transmit light within a specified range of wavelengthORthe instrument between telescope and detector may be one of several devices that spread the light out into its full rainbow of colors so that astronomers can measure individual lines in the spectrumSPECTROMETER.WHETHER FILTER OR SPECTROMETERstill have to use detectors to record and measure the properties of light.EX: A red transparent plastic is an everyday example of a filter that transmits only the red light and blocks the other colors. After the light passes through a filter, it forms an image that astronomers can then use to measure the apparent brightness and color of objects

which atoms have the greatest binding energy?

atoms with a mass near that of the iron nucleus (with a combined number of protons and neutrons equal to 56) and less for both the lighter and the heavier nuclei. Iron, therefore, is the most stable element: since it gives up the most energy when it forms, it would require the most energy to break it back down into its component particles.

why do blackbodies emit radiation (photons) of all wavelength(all colors)?

because in any solid or denser gas, some molecules or atoms vibrate or move between collisions slower than average and some move faster than average. So when we look at the electromagnetic waves emitted, we find a broad range, or spectrum, of energies and wavelengths. More energy is emitted at the average vibration or motion rate (the highest part of each curve), but if we have a large number of atoms or molecules, some energy will be detected at each wavelength.

what is the first evidence of absorption by interstellar clouds?

came from the analysis of a spectroscopic binary starWhile most of the lines in the spectrum of this binary shifted alternately from longer to shorter wavelengths and back again, as we would expect from the Doppler effect for stars in orbit around each other, a few lines in the spectrum remained fixed in wavelength.. The lines were also peculiar in that they were much, much narrower than the rest of the lines, indicating that the gas producing them was at a very low pressure. Subsequent work demonstrated that these lines were not formed in the star's atmosphere at all, but rather in a cold cloud of gas located between Earth and the binary star.

what is the relationship between electric & magnetic phenomena?

changing magnetic fields could produce electric currents (and thus changing electric fields), and changing electric currents could in turn produce changing magnetic fields. So once begun, electric and magnetic field changes could continue to trigger each other.

what is the collapse of a star and when does it happen?

collapse is the final event in the life of the core. Because the star's mass is relatively low, it cannot push its core temperature high enough to begin another round of fusion (in the same way larger-mass stars can). The core continues to shrink until it reaches a density equal to nearly a million times the density of water!At this extreme density, a new and different way for matter to behave kicks in and helps the star achieve a final state of equilibrium. In the process, what remains of the star becomes one of the strange white dwarfs

what are the three ways energy is transferred?

conduction, convection, radiationConduction and convection are both important in the interiors of planets. In stars, which are much more transparent, radiation and convection are important, whereas conduction can usually be ignored.

what is convection?

currents of warm material rise, carrying their energy with them to cooler layers. A good example is hot air rising from a fireplace.

Describe Jean Focault's demonstration for Earth's rotation?

demonstration of rotation--> started swinging pendulum evenly, if earth had not been turning there would have been no alteration to the path, but the pendulum's place of motion was turning --> Earth was turning beneath it As Earth turns, the plane of oscillation of the Foucault pendulum shifts gradually so that over the course of 12 hours, all the targets in the circle at the edge of the wooden platform are knocked over in sequence.

whats the difference between Low Mass Brown Dwarfs vs High Mass Planets

deuterium fusion. Although brown dwarfs do not sustain regular (proton-proton) hydrogen fusion, they are capable of fusing deuterium (a rare form of hydrogen with one proton and one neutron in its nucleus). The fusion of deuterium can happen at a lower temperature than the fusion of hydrogen. If an object has enough mass to fuse deuterium (about 13 MJ or 0.012 MSun), it is a brown dwarf. Objects with less than 13 MJ do not fuse deuterium and are usually considered planets.

what are the conclusions from the bohr model

each type of atom has its own unique pattern of electron orbits, and no two sets of orbits are exactly alike. This means that each type of atom shows its own unique set of spectral lines, produced by electrons moving between its unique set of orbits.

how does a planet move its host star?

ember that gravity is a mutual attraction. The star and the planet each exert a force on the other, and we can find a stable point, the center of mass, between them about which both objects move. The smaller the mass of a body in such a system, the larger its orbit. A massive star barely swings around the center of mass, while a low-mass planet makes a much larger "tour."

what is 99 percent of the material between stars made of?

gas—that is, it consists of individual atoms or molecules. The most abundant elements in this gas are hydrogen and helium (which we saw are also the most abundant elements in the stars), but the gas also includes other elements. Some of the gas is in the form of molecules—combinations of atoms.

What is Kepler's second law?

generalized that orbits of all planets are ellipsesSecond law deals with speed with which each planet moves along its ellipse= orbital speedSpeed up as it gets closer to the sun and slower as it pulls awayCovers the same amount of area in the same time intervalSpeed would be same in a circle but tends to vary because of elliptical orbit

what Aristarchus of Samos say about heliocentrism & why was his notion rejected?

he said that earth was center of universe however it was rejected by Aristotle and crew because they said if it was true we would see stars from different places in Earth's orbit and as the earth orbits the positions of stars would change relative to positions of distant stars

Figure 19.8 H-R Diagram of Stars Measured by Gaia and Hipparcos

his plot includes 16,631 stars for which the parallaxes have an accuracy of 10% or better. The colors indicate the numbers of stars at each point of the diagram, with red corresponding to the largest number and blue to the lowest. Luminosity is plotted along the vertical axis, with luminosity increasing upward. An infrared color is plotted as a proxy for temperature, with temperature decreasing to the right. Most of the data points are distributed along the diagonal running from the top left corner (high luminosity, high temperature) to the bottom right (low temperature, low luminosity). These are main sequence stars. The large clump of data points above the main sequence on the right side of the diagram is composed of red giant stars

Why isnt this true: if earth orbited sun we would observe the parallax of the nearer stars against the background of more distant objects as we viewed the sky from different parts of Earth's orbit?

how truly distant the stars were and how small the change in their positions therefore was, even with the entire orbit of Earth as a baseline. The problem was that they did not have tools to measure parallax shifts too small to be seen with the human eye. By the eighteenth century, when there was no longer serious doubt about Earth's revolution, it became clear that the stars must be extremely distant. Astronomers equipped with telescopes began to devise instruments capable of measuring the tiny shifts of nearby stars relative to the background of more distant (and thus unshifting) celestial objects.

What is the universe made of?

hydrogen, helium & carbn

what is the mathematical explanation for why hotter objects radiate more power at all wavelengths?

if we sum up the contributions from all parts of the electromagnetic spectrum, we obtain the total energy emitted by a blackbody. What we usually measure from a large object like a star is the energy flux, the power emitted per square meter.It turns out that the energy flux from a blackbody at temperature T is proportional to the fourth power of its absolute temperature--> Stefan Boltzmann Laws

how do we measure proper motion?

in arcseconds (1/3600 of a degree) per year. That is, the measurement of proper motion tells us only by how much of an angle a star has changed its position on the celestial sphere. If two stars at different distances are moving at the same velocity perpendicular to our line of sight, the closer one will show a larger shift in its position on the celestial sphere in a year's time.

what is light year?

is the distance that light (the fastest signal we know) travels in 1 year

what is the correct way to discuss binary systems ?

it is not correct to describe the motion of a binary star system by saying that one star orbits the other. Gravity is a mutual attraction. Each star exerts a gravitational force on the other, with the result that both stars orbit a point between them called the center of mass. Imagine that the two stars are seated at either end of a seesaw. The point at which the fulcrum would have to be located in order for the seesaw to balance is the center of mass, and it is always closer to the more massive star

what happens when a stable white dwarf can no longer contract or produce energy through fusion?

its only energy source is the heat represented by the motions of the atomic nuclei in its interior. The light it emits comes from this internal stored heat, which is substantial. Gradually, however, the white dwarf radiates away all its heat into space. After many billions of years, the nuclei will be moving much more slowly, and the white dwarf will no longer shine (Figure 23.5). It will then be a black dwarf—a cold stellar corpse with the mass of a star and the size of a planet. It will be composed mostly of carbon, oxygen, and neon, the products of the most advanced fusion reactions of which the star was capable.

how do larger interferometer seperations work?

larger interferometer separations can be achieved if the telescopes do not require a physical connection. Astronomers, with the use of current technology and computing power, have learned to time the arrival of electromagnetic waves coming from space very precisely at each telescope and combine the data later. If the telescopes are as far apart as California and Australia, or as West Virginia and Crimea in Ukraine, the resulting resolution far surpasses that of visible-light telescopes

how can excited atom lose excess energy?

lose its excess energy either by colliding with another particle or by giving off a radio wave with a wavelength of 21 centimeters. If there are no collisions, an excited hydrogen atom will wait an average of about 10 million years before emitting a photon and returning to its state of lowest energy. Even though the probability that any single atom will emit a photon is low, there are so many hydrogen atoms in a typical gas cloud that collectively they will produce an observable line at 21 centimeters.

What are T Tauri stars?

may actually be stars in a middle stage between protostars and hydrogen-fusing stars such as the Sun. High-resolution infrared images have revealed jets of material as well as stellar winds coming from some T Tauri stars, proof of interaction with their environment.

astronomers call all the elements heavier than helium...

metals,even though most of them do not show metallic properties.

describe individual grains

must be just slightly smaller than the wavelength of visible light. If the grains were a lot smaller, they would not block the light efficiently, as Figure 20.13 and other images in this chapter show that it does.On the other hand, if the dust grains were much larger than the wavelength of light, then starlight would not be reddened. Things that are much larger than the wavelength of light would block both blue and red light with equal efficiency. In this way we can deduce that a characteristic interstellar dust grain contains 106 to 109 atoms and has a diameter of 10-8 to 10-7 meters (10 to 100 nanometers)

Stefan-Boltzmann law for the relationship between energy radiated and temperature?

n this method, the energy flux (energy emitted per second per square meter by a blackbody, like the Sun) is given byF = σT ^4where σ is a constant and T is the temperature. The surface area of a sphere (like a star) is given byA = 4πR^2The luminosity (L) of a star is then given by its surface area in square meters times the energy flux:L = (A × F)

what are objects?

objects even cooler than M9-type stars. We use the word object because many of the new discoveries are not true stars. A star is defined as an object that during some part of its lifetime derives 100% of its energy from the same process that makes the Sun shine—the fusion of hydrogen nuclei (protons) into helium. Objects with masses less than about 7.5% of the mass of our Sun (about 0.075 MSun) do not become hot enough for hydrogen fusion to take place.

how do we measure diameter of stars covered by moon?

observe the dimming of light that occurs when the Moon passes in front of a star. What astronomers measure (with great precision) is the time required for the star's brightness to drop to zero as the edge of the Moon moves across the star's disk. Since we know how rapidly the Moon moves in its orbit around Earth, it is possible to calculate the angular diameter of the star. If the distance to the star is also known, we can calculate its diameter in kilometers. This method works only for fairly bright stars that happen to lie along the zodiac, where the Moon (or, much more rarely, a planet) can pass in front of them as seen from Earth.

How many years a star remains in the main-sequence band depends on...

on its mass. You might think that a more massive star, having more fuel, would last longer, but it's not that simple. The lifetime of a star in a particular stage of evolution depends on how much nuclear fuel it has and on how quickly it uses up that fuel. (In the same way, how long people can keep spending money depends not only on how much money they have but also on how quickly they spend it. This is why many lottery winners who go on spending sprees quickly wind up poor again.) In the case of stars, more massive ones use up their fuel much more quickly than stars of low mass.

What is the circumpolar zone? (how does it explain what we see about stars in the sky?)

one of the polar regions of the Earth's sky. Denotes that a from an observer's perspective the star never leaves the sky during its diurnal motion The closer you are to the poles the greater the portion of the sky that is visible Polaris moves in the least in the sky

how often do supernovas occur?

one supernova explodes roughly every 100 years somewhere in the Galaxy. On average, shocks launched by supernovae sweep through any given point in the Galaxy about once every few million years. These shocks keep some interstellar space filled with gas at temperatures of millions of degrees, and they continually disturb the colder gas, keeping it in constant, turbulent motion.

What is helioseismology important tool for?

or predicting solar storms that might impact Earth. Active regions can appear and grow large in only a few days. The solar rotation period is about 28 days. Therefore, regions capable of producing solar flares and coronal mass ejections can develop on the far side of the Sun, where, for a long time, we couldn't see them directly.Fortunately, we now have space telescopes monitoring the Sun from all angles, so we know if there are sunspots forming on the opposite side of the Sun. Moreover, sound waves travel slightly faster in regions of high magnetic field, and waves generated in active regions traverse the Sun about 6 seconds faster than waves generated in quiet regions. By detecting this subtle difference, scientists can provide warnings of a week or more to operators of electric utilities and satellites about when a potentially dangerous active region might rotate into view. With this warning, it is possible to plan for disruptions, put key instruments into safe mode, or reschedule spacewalks in order to protect astronauts.

What is a meridian?

perpendicular to and cross the equator at right angles (any point on Earth will have a meridian through it) the meridian specifies the east-west location

whats the purpose of photographic & electronic Detectors?

photographic film or glass plates served as the prime astronomical detectors, whether for photographing spectra or direct images of celestial objects.

what are charged couple devices (CCDs)?

photons of radiation hitting any part of the detector generate a stream of charged particles (electrons) that are stored and counted at the end of the exposure. Each place where the radiation is counted is called a pixel (picture element), and modern detectors can count the photons in millions of pixels

how is an astronomical radio receiver like a spectrometer on visible/infrared light?

providing information about how much radiation we receive at each wavelength or frequency. After computer processing, the radio signals are recorded on magnetic disks for further analysis.

What causes tides? How does the moon effect the Earth?

results from the gravitations forces exerted by the Moon at several points on EarthForces differ slightly from one another= all parts are not equally distant from the moon or in the same directionthe differences among the forces of the Moon's attraction on different parts of Earth (called differential forces) cause Earth to distort slightly.Side closest is most attracted that side opposite moon = differential forces tend to stretch Earth into prolate spheroid (a football shape) , long diameter pointed towards the moonMeasurements of the actual deformation of Earth show that the solid Earth does distort, but only about one-third as much as water would, because of the greater rigidity of Earth's interior.Because the tidal distortion of the solid Earth amounts—at its greatest—to only about 20 centimeters, Earth does not distort enough to balance the Moon's differential forces with its own gravity. Hence, objects at Earth's surface experience tiny horizontal tugs, tending to make them slide about. These tide-raising forces are too insignificant to affect solid objects like astronomy students or rocks in Earth's crust, but they do affect the waters in the ocean

how much of our stars do white dwarfs make up?

shows that about 7% of the true stars (spectral types O-M) in our local neighborhood are white dwarfs. A good example of a typical white dwarf is the nearby star 40 Eridani B. Its surface temperature is a relatively hot 12,000 K, but its luminosity is only 1/275 LSun. Calculations show that its radius is only 1.4% of the Sun's, or about the same as that of Earth, and its volume is 2.5 × 10-6 that of the Sun. Its mass, however, is 0.57 times the Sun's mass, just a little more than half.To fit such a substantial mass into so tiny a volume, the star's density must be about 210,000 times the density of the Sun, or more than 300,000 g/cm3. A teaspoonful of this material would have a mass of some 1.6 tons! At such enormous densities, matter cannot exist in its usual state; we will examine the particular behavior of this type of matter in The Death of Stars. For now, we just note that white dwarfs are dying stars, reaching the end of their productive lives and ready for their stories to be over

The main-sequence lifetimes of stars of different masses?

smaller stars have longer life spans

what is the speed at which electromagnetic disturbances moves through space?

speed of light--> lead to conclusion that light was one form of a family of possible electromagnetic disturbances called electromagnetic radiation (verified experimentally)

is star formation an efficient process?

star formation is not a very efficient process. In the region of the Orion Nebula, about 1% of the material in the cloud has been turned into stars. That is why we still see a substantial amount of gas and dust near the Trapezium stars. The leftover material is eventually heated, either by the radiation and winds from the hot stars that form or by explosions of the most massive stars.Whether gently or explosively, the material in the neighborhood of the new stars is blown away into interstellar space. Older groups or clusters of stars can now be easily observed in visible light because they are no longer shrouded in dust and gas

Why are we missing most of the brightest stars when we take our census of the local neighborhood?

stars that appear brightest are not the ones closest to us. The brightest stars look the way they do because they emit a very large amount of energy—so much, in fact, that they do not have to be nearby to look brilliant.distances for the 20 stars that appear brightest from Earth. The most distant of these stars is more than 1000 light-years from us. In fact, it turns out that most of the stars visible without a telescope are hundreds of light- years away and many times more luminous than the Sun. Among the 6000 stars visible to the unaided eye, only about 50 are intrinsically fainter than the Sunmost are spectral type B

what stars end up as white dwarfs?

stars with starting masses up to at least 8 MSun (and perhaps even more)

Explain Sun's illumination/ position in the sky on the summer solstice in the Northern Hemisphere

summer solstice: the Sun shines down most directly upon the Northern Hemisphere of Earth. It appears about 23° north of the equator, and thus, on that date, it passes through the zenith of places on Earth that are at 23° N latitude To a person at 23° N (near Hawaii, for example), the Sun is directly overhead at noon. This latitude, where the Sun can appear at the zenith at noon on the first day of summer, is called the Tropic of Cancer. As Earth turns on its axis, the North Pole is continuously illuminated by the Sun; all places within 23° of the pole have sunshine for 24 hours. The Sun is as far north on this date as it can get; thus, 90° - 23° (or 67° N) is the southernmost latitude where the Sun can be seen for a full 24-hour period (sometimes called the "land of the midnight Sun"). That circle of latitude is called the Arctic Circle.

What is Earth's satellite?

the Moon (takes one month to complete one revolution)

What is two reasons Aristotle say earth is round?

the earth is round because 1. as the moon enters and emerges from the earth's shadow the shadow on the moon is round 2. travelers go far south are able to observe stars that are not visible in the north & as you move from north to south stars disappear from view And the height of the North Star—the star nearest the north celestial pole—decreases as a traveler moves south. *** only explanation is curvature of earth

what happens to the neutrino that forms in step 1?

the fusion of two hydrogen atoms to form deuterium results in the emission of a neutrino. Because neutrinos interact so little with ordinary matter, those produced by fusion reactions near the center of the Sun travel directly to the Sun's surface and then out into space, in all directions. Neutrinos move at nearly the speed of light, and they escape the Sun about two seconds after they are created.

what is spectrometer?

the instrument between telescope and detector may be one of several devices that spread the light out into its full rainbow of colors so that astronomers can measure individual lines in the spectrum.allows astronomers to measure (to meter) the spectrum of a source of radiation.

describe the spectra of class L brown dwarfs

the lines of titanium oxide, which are strong in M stars, have disappeared.This is because the L dwarfs are so cool that atoms and molecules can gather together into dust particles in their atmospheres; the titanium is locked up in the dust grains rather than being available to form molecules of titanium oxide

what happens after the neutrons that they cannot be held?

the neutrons are squeezed out of the nuclei and can exert a new force. As is true for electrons, it turns out that the neutrons strongly resist being in the same place and moving in the same way. The force that can be exerted by such degenerate neutrons is much greater than that produced by degenerate electrons, so unless the core is too massive, they can ultimately stop the collapse.

What is the horizon?

the point where the sky meets the earth (the dome meets the earth)

what is chromatic aberration?

the property of a lens whereby light of different colors is focused at different places = causes image to appear blurry

what does the doppler shift method rely on ?

the pull of a planet making its star "wiggle" back and forth around the center of mass—is most effective at finding planets that are both close to their stars and massive. These planets cause the biggest "wiggles" in the motion of their stars and the biggest Doppler shifts in the spectrum. Plus, they will be found sooner, since astronomers like to monitor the star for at least one full orbit (and perhaps more) and hot Jupiters take the shortest time to complete their orbit.

What are the implications for the Sun & Earth when taking the ecliptic path?

the rises 4 minutes later each day with respect to the day this also requires the earth to make slightly more than one rotation

What is a scientific law?

the same underlying principles that guide the universe and apply to all applications of a principle a model that is consistently successful and can be relied on to predict the nature of the universe = law

What happens to seasons as you get closer to the poles?

the seasons become more pronounced at the poles and opposite not as pronounced in the equator

What is cosmology?

the study of the structure ,origin & function of the cosmos

What are notable parts of the ellipse formation?

the sum of the distances from the two foci to any point on the ellipse is the same the widest diameter is the major axis and half this length the ratio of the distance between the two foci and major axis = eccentricity close to 1 eccentricity more circular

What is the universe?

the sum total of all matter and energy

what is the suns position (degrees) relative to the stars?

the sun moves 1 degrees east relative to the stars

what nuclear reaction occur in the sun's interior?

the sun taps taps the energy contained in the nuclei of atoms through nuclear fusion

why couldn't they detect hydrogen in interstellar cloud spectra?

they could not yet detect hydrogen, the most common element, due to its lack of spectral features in the visible part of the spectrum.The Balmer line of hydrogen is in the visible range, but only excited hydrogen atoms produce it. In the cold interstellar medium, the hydrogen atoms are all in the ground state and no electrons are in the higher-energy levels required to produce either emission or absorption lines in the Balmer series.)Direct detection of hydrogen had to await the development of telescopes capable of seeing very-low-energy changes in hydrogen atoms in other parts of the spectrum. The first such observations were made using radio telescopes, and radio emission and absorption by interstellar hydrogen remains one of our main tools for studying the vast amounts of cold hydrogen in the universe to this day.

what is geo centrism?

this is the theory during the renaissance that placed earth as the center of space and us in the middle of the cosmos

The natural turbulence inside a clump tends to...

to give any portion of it some initial spinning motion (even if it is very slow). As a result, each collapsing core is expected to spin. According to the law of conservation of angular momentum (discussed in the chapter on Orbits and Gravity), a rotating body spins more rapidly as it decreases in size. In other words, if the object can turn its material around a smaller circle, it can move that material more quickly—like a figure skater spinning more rapidly as she brings her arms in tight to her body. This is exactly what happens when a core contracts to form a protostar: as it shrinks, its rate of spin increases.

what will the wind from a forming star do ?

ultimately sweep away the material that remains in the obscuring envelope of dust and gas, leaving behind the naked disk and protostar, which can then be seen with visible light. We should note that at this point, the protostar itself is still contracting slowly and has not yet reached the main- sequence stage on the H-R diagram (a concept introduced in the chapter The Stars: A Celestial Census). The disk can be detected directly when observed at infrared wavelengths or when it is seen silhouetted against a bright background

what happens if convection doesn't occur?

unless convection occurs, the only significant mode of energy transport through a star is by electromagnetic radiation. Radiation is not an efficient means of energy transport in stars because gases in stellar interiors are very opaque, that is, a photon does not go far (in the Sun, typically about 0.01 meter) before it is absorbed. (The processes by which atoms and ions can interrupt the outward flow of photons—such as becoming ionized—were discussed in the section on the Formation of Spectral Lines.) The absorbed energy is always reemitted, but it can be reemitted in any direction. A photon absorbed when traveling outward in a star has almost as good a chance of being radiated back toward the center of the star as toward its surface.A particular quantity of energy, therefore, zigzags around in an almost random manner and takes a long time to work its way from the center of a star to its surface (Figure 16.13). Estimates are somewhat uncertain, but in the Sun, as we saw, the time required is probably between 100,000 and 1,000,000 years. If the photons were not absorbed and reemitted along the way, they would travel at the speed of light and could reach the surface in a little over 2 seconds, just as neutrinos do

what kind of telescope collect visible radiation?

use a lens or mirror to gather the light.

describe the relationship between speed & temperature

when the temperature is higher, so are the speed and energy of the collisions. The hotter the gas, therefore, the more likely that electrons will occupy the outermost orbits, which correspond to the highest energy levels. This means that the level where electrons start their upward jumps in a gas can serve as an indicator of how hot that gas isabsorption lines in a spectrum give astronomer info about the temperature of the regions where the lines originate

what is the Stefan-Botlzmann Law?

where F stands for the energy flux and σ (Greek letter sigma) is a constant number (5.67 × 10-8).