Astronomy Midterm UCLA, Astronomy Final

Speed of light and how to calculate it

186,000 mi/s 300,000 km/s Speed= distance/time

The daily and annual motion of stars in the sky

"Rise in the east and set in the west" The night sky changes throughout the year because of Earths changing position in its orbit around the sun causing stars to "move" to different places in the sky

Know how we define an "active" galactic nucleus, in terms of brightness, spectra or radio properties.

- An unusually active galaxy is distinguished from a more normal galaxy by exhibiting a form or level of emission that exceeds that expected based only on the stars and gas present in that galaxy. In 1943, Carl Seyfert noted that a small fraction of galaxies have nuclei which exhibit high ionization emission lines. Such nuclei are extremely luminous and outshine the rest of the galaxy. -The spectrum of a Seyfert 1 galaxy shows broad lines of Hydrogen emission but narrow lines of Oxygen. The broadening of the Hydrogen lines suggest the gas is moving with velocities of 1000-5000 km/s, while the gas that emits Oxygen lines is only moving at 500 km/s ese are even rarer than Seyfert galaxies - It appears as though something in the center of the galaxy produces collimated jets of high energy plasma (charged particles such as electrons, positrons and positively charged ions) These jets propagate out from the galaxy and power giant radio emitting lobes on either side. The spectrum of the emission from the jets and the radio lobes show that it is synchrotron emission, which is the emission of high energy electrons spiralling around magnetic fields (the same process as produces emission in pulsars).

How is a white dwarf related to a Planetary Nebula?

-The Planetary Nebula. The white dwarf also plays a role in the fate of the ejected outer layers of the star. ... Astronomers called them planetary nebulae because of their observational similarity to Uranus, but we now know they are the remnants of dead stars and have nothing to do with planets -Planetary nebulae came to be understood as a final stage of stellar evolution. Spectroscopic observations show that all planetary nebulae are expanding. This led to the idea that planetary nebulae were caused by a star's outer layers being thrown into space at the end of its life.

Luminosities range from?

0.0001 to 1000000 times the luminosity of the Sun. The low end corresponds to 0.08 solar masses andthe bright end to 100 solar masses.

Newtons laws Of motion

1. In the absence of a net force, and object will move with constant velocity. Objects at rest tends to remain at rest and object in motion tends to remain in motion with no change in either their speed or their direction. 2. Force equals mass times acceleration. 3. Every force is always paired with an equal and opposite reaction force

Kepler's three laws of planetary motion

1. the orbit of each planet about the sun is an ellipse with the sun at one focus (A planets distance from the sun varies during its orbit) 2. As a planet moves around its elliptical orbit, it moves faster when it's nearer the sun and slower when it is farther from the sun, sweeping out equal areas in equal times. 3. More distant planets orbit the sun at slower average speeds

Open Cluster

A few thousand loosely packed stars

What is the Helium flash?

A helium flash is a very brief thermal runaway nuclear fusion of large quantities of helium into carbon through the triple-alpha process in the core of low mass stars (between 0.8 solar masses (M☉) and 2.0 M☉) during their red giant phase - Helium flash is caused by the ignition of helium fusion in a core that contains degenerate electrons. The degenerate electrons control the pressure of the core and because they are degenerate, do not readily expand with an increase in temperature.

Eclipsing binary

A pair of stars that orbit in the plane of our line of sight. When neither star is eclipsed, we see the combined light of both stars. When one star eclipses the other, the apparent brightness of the system drops because some of the light is blocked from our view

What are quasars?

A quasar is an active galactic nucleus of very high luminosity. The name "Quasar" = Quasi-Stellar Radio Source. A distinguishing feature of these objects were strong emission lines, which are not usually found in stars.

Solar vs sidereal day

A solar day is the time it takes for the Earth to rotate about its axis so that the Sun appears in the same position in the sky. The sidereal day is ~4 minutes shorter than the solar day. The sidereal day is the time it takes for the Earth to complete one rotation about its axis with respect to the 'fixed' stars.

How do telescopes allow us to see fainter things and things at higher resolution? What do we mean by angular resolution?

A telescope's spatial resolution is also related to the span of its optics (lenses or mirrors). A larger baseline (effective diameter) increases spatial resolution, the ability to see detail in objects; this larger baseline can be achieved by both larger single primary mirrors and by using multiple mirrors together (even if they are spaced apart) With more light we can create a brighter image, we can then magnify the image so that it takes up more space on our retina. The big lens in the telescope (objective lens) collects much more light than your eye can from a distant object and focuses the light to a point (the focal point) inside the telescope Angular resolution:Angular resolution or spatial resolution describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object, thereby making it a major determinant of image resolution.

What is adaptive optics

Adaptive optics essentially makes a telescope's mirrors do an opposite dance as the blurring caused by the atmosphere, canceling out the atmospheric distortions

Atom Isotope Molecule

An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element Versions of an element with different number of neutrons are called isotopes A molecule is an electrically neutral group of two or more atoms held together by chemical bonds.

Know the evidence that suggests the dinosaurs were wiped out by a large asteroid strike

And iridium which sediment layer and a 65 million-year-old crater show that a large impact occurred at the time the dinosaurs died out

Understand definitions of degrees, minutes and seconds of arc and how they define angular size.

Angular size: The angle it appears to span in your field of view. Angular distance: The angle that appears to separate pairs of objects in the sky For greater precision, we subdivide each degree into 60 arcminutes each are arcminute into 60 arcseconds.

Retrograde motion

Apparent retrograde motion is the apparent motion of a planet in a direction opposite to that of other bodies within its system, as observed from a particular vantage point.

What is interferometry

Astronomers have developed a technology known as interferometry, which can allow multiple telescopes to work together to achieve an angular resolution equivalent to that of a much larger single telescope

direct imaging, microlensing, astrometry, transit timing

At its heart, the direct-imagingmethod resembles photography, whether via visible or infrared light. But photographing a planet isn't easy, especially when it is literally outshone by its parent star. Scientists must use an instrument known as a coronagraph to block the light from the star, revealing the dimmer light reflected by a planet in its shadow. Microlensing: A type of gravitational lensing in which the light of a star is temporarily magnified as another star passes in front of it and beans it's late. Careful study of the microlensing event can review whether the foreground star has planets. Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. Transit-timing variation is a method for detecting exoplanets by observing variations in the timing of a transit. This provides an extremely sensitive method capable of detecting additional planets in the system with masses potentially as small as that of Earth. In tightly packed planetary systems, the gravitational pull of the planets among themselves causes one planet to accelerate and another planet to decelerate along its orbit. The acceleration causes the orbital period of each planet to change detecting this effect by measuring the change is known as Transit Timing Variations.[1][2][3][4][5][6] "Timing variation" asks whether the transit occurs with strict periodicity or if there's a variation.

Astronomical unit

Average distance between the Earth and the Sun (150 million kilometers)

How do we "see" black holes?

Black holes emit no light. At a large enough distance from a black hole, the gravity behaves just like Newton's gravity, so another body will follow the same orbit if the companion is a regular star or a black hole. For some binary stars, we can see radial velocity variations that indicate that it is orbiting a massive, dark object. Some black holes are found in binaries where the other star is sufficiently evolved that it can transfer material. In this case, we can see emission from the hot gas in the disk (called the accretion disk) as it orbits the black hole. Supermassive black holes can be found in the centers of galaxies. In the Milky Way Galactic center, we can trace the orbits of multiple stars orbiting the central mass. The best way to test the notion of black holes is to see the warping of space-time directly. This can be done by studying gravitational waves - waves in the space-time warp that propagate through space

How do we get the age of the solar system?

By doing radio metric dating on meteorites

The internal structure of earth

Core: The highest density material, consisting primarily of metals such as nickel and iron, reside in the central core Mantle: Rocky material of Moderat density, mostly minerals that contain silicone, oxygen, and other elements. Crust: The lowest density rock forms a thin crust, essentially representing the worlds outer skin

What determines the length of a day/year

Day: the time it takes to complete one full rotation on its axis Year: the time the planet takes to make one full revolution around the sun

Know the different components of the galaxy (disk, bulge, halo) and their approximate sizes.

Disk: Seen edge-on, the Milky Way is a flatenned disk of stars, with a central concentration or "bulge". The disk is about 1000 light years thick. The stars are distributed across a region that is about 30 kiloparsecs across (= 30000 parsecs, about 100,000 light years) Halo: The main disk part is also surrounded by a spherically distributed halo of stars. It is about 100 kiloparsecs across and also contains individual stars, but very little gas or dust. Buldge: the buldge is a round structure made primarily of old stars and dust The buldge is roughly 10,000 light years across. Thickness of the buldge is about 16,000 light years.

The inverse square law for light

Doubling the distance to a star would decrease its apparent brightness by a factor of 2^2, or 4

Understand the different stages of the universe as it expanded and cooled, which determines what forces dominate at a given time

Electromagnetism - responsible for light and atoms Gravity- responsible for most large scale dynamics Weak Nuclear Force - responsible for radioactivity Strong Nuclear Force - responsible for holding nuclei together GUT era - lasts from about 10 s (the Planck time, which is when we expect gravity to merge with the other forces) to about 10 s. The Universe may have expanded very rapidly under these conditions Electroweak era: this is the time when the weak and electromagnetic forces are comparable. The universe is characterised by an intense radiation field and continuous creation and annihilation of particles. The universe continues to expand and cool, until it reaches temperatures that are about 100 million times the temperature in the core of the Sun. At this point the weak and electromagnetic forces become decoupled, and the balance of forces starts to be similar to that which we see today. The Particle era: As the weak and electromagnetic forces decouple, at lot of particles are created from photons, and the universe contains roughly equal amounts of matter and antimatter. Eventually the universe expands to the point where it is too cool to continue to create particles from photons. At this point most of the antimatter annihilates with matter, tilting the balance heavily in favour of photons. There is a small excess of matter over antimatter (roughly 1 extra proton for every 10 proton-antiproton pairs), and this is what is responsible for the matter we see today. The rest gets converted into radiation, which is the dominant energy reservoir at this time. The Era of Nucleosynthesis: As the universe cools further, it starts to reach temperatures that one finds today in the cores of stars. This means that nuclear reactions start to occur - with protons and neutrons merging to form Deuterium (Hydrogen with 1 neutron) and Tritium (Hydrogen with 2 neutrons), Helium and Lithium. An important difference with the case of a stellar core is that the universe is expanding and getting cooler and less dense. This limits how far the fusion can proceed before things get too cool. This is why we get mostly H and He from the Big Bang. If the expansion happened more slowly, we might have gotten more heavy elements like Carbon or Oxygen. The Era of Atoms: As long as photons are energetic enough to unbind electrons from nuclei, the material in the universe remains ionized. Eventually (after about 380,000 years) atoms can form, when the temperature of the ambient radiation drops below a few thousand degrees K. This is also when the universe becomes transparent to radiation i.e. photons can travel from this epoch to our telescopes without being completely absorbed by material along the way. This produces a "background glow" that we can observe as the Cosmic Background Radiation. The Era of Galaxies: After the decoupling of radiation and matter, this becomes the observable universe. Dark matter is not coupled to radiation and so starts to clump together under gravity even before this, but the clumps grow slowly with time. At decoupling they are partially formed but continue to collapse and get deeper. Once gas is no longer subject to the radiation pressure it can also start to fall into the gravitational potential wells, leading to the formation of galaxies.

What are emission, absorption, transmission and reflection? How do these relate to color?

Emission: A light bulb emits visible light; energy of the light comes from e,E tribal potential energy supplied to the bulb Absorption: When you place your hand near an incandescent light hand absorbs some of the light, and this absorbed energy warms your hand Transmission: Some forms of matter, such as glass and air. Transmit light, which means a,knowing it to pass through Reflection: Light can bounce off matter, leading to what we call reflection(when the bouncing is all in the same general direction) The light coming from each object therefore carries an enormous amount of info ration about the o nests location, shape structure, and composition. Your brain interprets the messages that light carries, recognizing materials and objects in the process we call vision

What are the sources of the colours in the giant planet atmospheres?

For Jupiter and Saturn Light is reflected off of the ammonium hydrosulfide clouds. The cold temperatures on Uranus and Neptune allow some of their abundant methane gas to condense of the clouds. Methane gas also absorbs red light, allowing only blue light to penetrate to the level at which the methane clouds form.

Synchronous Rotation Why was it caused by tides?

From Earth we always see (nearly) the same face of the moon . This happens because the moon rotates on its axis in the same amount of time it takes to orbit Earth It's a consequence of Earths of gravity affecting the moon in much the same way the moons gravity causes tides on Earth. Synchronous rotation is the result of tidal forces that over time slow the rotation of the smaller body until it is synchronized with its period of revolution around the larger body.

properties of the surface of Titan

Has a thick atmosphere that we cannot see through with visible light. Titans reddish color comes from chemicals and its atmosphere. The atmosphere is more than 95% nitrogen, while the rest consists of Argon and methane, ethane and other hydrogen compounds. Greenhouse effect make it warmer than it would be otherwise. Lakes of liquid ethane and methane

Epicycle

He believed that this cyclical variation could be represented visually by mini orbits, or epicycles, revolving around larger circular orbits, or deferents a small circle the center of which moves around in the circumference of a larger circle: used in Ptolemaic astronomy to account for observed periodic irregularities in planetary motions.

At all wavelengths?

Hotter object objects emit more light

Speed Velocity Acceleration Acceleration due to gravity

How far something will go in a certain amount of time. The speed and the direction of an object. A change in velocity The acceleration of the following object. On earth, the acceleration of gravity causes falling objects to thaw faster by 9.8 m/s with each passing second.

Understand how we now have strong evidence for three broad classes of planet

Hydrogen rich extrasolar planets vary intensity by a factor of 100, rangefar greater than the density range we observe in our solar system, but it seems reasonable to think that much of this range is attributable to increases in temperature caused by some Jovian planets being very close to their stars. Some planets appear to be Water worlds and maybe predominantly made of water, either in liquid form or as a high-pressure solid, or perhaps other hydrogen compounds. Alternatively some of these worlds might be composed of a dense rocky/metallic core and a thick layer of low density of hydrogen and helium gas. Scientist believe that extrasolar Jovian planets were indeed born with circular orbits far from there stars and that those that now have close-in orbits underwent some sort of planetary migration. Waterworld planets may be similar to Uranus and Neptune, though in some cases much smaller. These world may have been much like the ice rich planetesimals that seeded them formation of Jovian planets in our solar system. in that case, perhaps whether water worlds exist depend on when a star clears it's nebular gas, halting the epoch of planet formation.

The processes that alter Earths surface

Impact cratering: the creation of impact craters by astroids or comets striking a planet surface Volcanism: the erruption of molten rock or lava from the planets interior onto its surface Tectonics: the disruption of a planet surface by internal stresses. Erosion: the wearing down or building up of geological features by wind, water, ice, and other phenomena of planetary weather

What is the habitable zone?

In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.

Understand Hubble's relation between distance and velocity, and what is the Hubble constant?

In the 1920s, Edwin Hubble used the Mount Wilson telescope to detect and measure Cepheid stars in nearby galaxies and thereby determine the distances to them. Comparing the distances and the redshifts, he noted that there was a correlation, namely that more distant galaxies also exhibited larger redshifts, i.e. they were moving faster. The constant of proportionality is called Hubble's constant, and modern measurements give a value of about 70 kilometers per second per Megaparsec. The resulting inference is that the universe is expanding, in all directions, at once. z = H d/c The Hubble Constant is the unit of measurement used to describe the expansion of the universe.

the large moons of Jupiter and Saturn

Jupiter: io, Europa, Ganymede, and Callisto (Galilean moons) Saturn: Enceladus, Titan, Tethys, Dione, Rhea, Iapetus, Mimas

Tides and the structure of io and Europa

Jupiters mass makes its tidal force exerted on Io far larger than the tidal force the earth exerts on the moon. The result is that IO is continuously being flexed in different directions, which generates friction inside it. The flexing heats the interior. Tidal Heating generates tremendous heat on Io and calculations show that his he can explain the incredible volcanic activity Tidal heating may create a deep ocean of liquid water beneath Europa's icy crusty.

The different kinds of energy

Kinetic energy: Energy of motion Radiative energy: Energy carried by light Potential energy: stored energy Thermal energy: collective kinetic energy Gravitational potential energy: an objects gravitational potential energy depends on its mass and how far you can fall as a result of gravity. mass energy: Mass it's self is a form of potential energy

How planet cooling depends on size and why

Larger planets retain internal heat much longer than smaller ones and this heat drives geological activity. The size of the planet determines planetary cooling. Extra layers act as insulation, thus taking longer for internal heat to reach the surface The total amount of heat contained in a planet depends on its volume, but heat can escape into space only from the planet surface. As heat escapes, more heat flows upward from the interior to replace it until the interior is no hotter than the surface. As the planet cools, geological activity ceases.

What is the solar cycle?

Long term monitoring shows that this number is approximately periodic, with an 11 year period. The solar cycle or solar magnetic activity cycle is the nearly periodic 11-year change in the Sun's activity (including changes in the levels of solar radiation and ejection of solar material) and appearance (changes in the number and size of sunspots, flares, and other manifestations).

Understand how the luminosity, temperature and radius of a star are related. How does its brightness depend on distance from us?

Luminosity is the power radiated by star (so energy output per second). The units are joules per second=Watts To determine luminosity, we need to know the temperature and radius of the star As the size of a star increases, luminosity increases. If you think about it, a larger star has more surface area. That increased surface area allows more light and energy to be given off. L=R^2(T^4) A hotter star is more luminous than a cooler one of the same radius. A bigger star is more luminous than a smaller one of the same temperature. The apparent brightness of a star is proportional to 1 divided by its distance squared. That is, if you took a star and moved it twice as far away, it would appear 1/4 as bright; if you moved it four times the distance, it would appear 1/16 as bright. - The variation in their brightness is caused by both variations in their luminosity and variations in their distance. An intrinsically faint, nearby star can appear to be just as bright to us on Earth as an intrinsically luminous, distant star. So, to determine the apparent brightness of a star we need to know how bright it is intrinsically (the luminosity) and how far away it is.

general properties of things discovered (short periods, circumbinary, in the habitable zone etc)

Many of them orbit quite close to their star despite being as large is Jupiter Many had large eccentricities Planets are common, 70% of stars harbor atleast one planet Small planets appear to outnumber large planets by a significant margin. Most of the planets are probably too hot to harbor life because of their clothes or back to their stars About 20% of stars are likely to have a planet less than twice Earth size in an orbit within the region around the start and which liquid water could potential he exist on the planet surface, the habitable zone Some orbit two star The density range for extrasolar planets is significantly wider than that for the planets in our own solar system

The Ice Line

Marked the key transition between the warm into regions of the solar system where terrestrial planets formed in the cool outer regions where Jovian planets formed. Inside the frost line, only metal and rock could condense into solid seeds. Beyond the frost line, the solid seeds were built of ice along with metal and rock.

Classification of stars

Massive, hot stars appear bluer and cooler, lower mass stars appear red. • The Sun lies somewhere in the middle, with a yellow color.

Which are the most common types of main sequence stars and which are the rarest?

Most stars are low-mass (of M or K spectral type) and the frequency gets lower as you go to higher mass stars (O and B are the rarest kind)

Newtons law of gravitation (Kepler variation)

Newton's law of universal gravitation states that a particle attracts every other particle in the universe using a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. Newtons version of Kepler's third law allows us to calculate the masses of distant objects

Understand how nuclear reactions in the expanding universe determine the amount of Helium and Deuterium in the universe

Nuclear Fusion reactions (Nucleosynthesis) during the hot, dense phase is also responsible for the ratio of Hydrogen and Helium in the universe Big Bang Nucleosynthesis: We can also get constraints on the evolution of the early universe from the relative amounts of Helium and Deuterium in the universe. The rate of expansion and the relative density of matter and radiation will determine the nuclear reaction rates and thus the abundances. The models that fit this data suggest that only about 4.4% of the mass in the universe is in the form of baryon. This is an independent verification of the idea that dark matter must be composed of non-baryonic matter

How do we measure the distance of stars?

Parallax:the semi-angle of inclination between two sight-lines to the star, as observed when Earth is on opposite sides of the Sun in its orbit. -Measuring the parallax angle (p), the angle would be smaller if the star were farther away, meaning that more distant stars have smaller parallax angles Stellar Parallax

What are constellations? The celestial sphere?

Patterns of stars; A region in the sky with well-defined borders; the familiar patterns of stars merely helps us locate these constellations The stars and constellations lie on a great sphere that surrounds earth

can be much larger than in the solar system and planets can be much closer to their parent stars than Mercury

Planet eccentricities

What is the difference between primitive and processed asteroids?

Primitive in the sense of being remnants from the time when solid material first condensed from the solar nebula. Processed in the sense that, unlike the primitive meteorites, they have been remade overtime. More specifically, processed meteor rights appear to have come from astroids that were large enough to have undergone differentiation into a core mantle crust structure.

Diffusion or Convection?

Radiative diffusion occurs in any hot gas. However, it is a slow process, and if the heat builds up, the temperature difference between core and surface increases. Beyond a threshold difference, it becomes more efficient for the fluid to move as parcels - this is convection.

What are the origins of the giant planet rings?

Ring systems probably owe their existence to small moons formed in the disks of gas that produce the Jovian planets billions of years ago. The rings with you today are composed of particles liberated from those moons quite recently. The numerous moonlets that formed of the disks of material orbiting the young Jovian planets are gradually been grind it down by tiny impacts.

how the method of detecting planets via transits works. What physical properties can we infer from this, and what are the biases?

Searching for slight changes in a stars brightness caused by orbiting planets. The result is a transit, in which the planet appears to move across the face of the star, causing a small, temporary dip in the system's brightness. The transit message searches for transits and eclipses by carefully monitoring a stars systems brightness over an extended period of time. The larger the planet the more dimness it will cause. Some planets that are discovered are considered candidates because even though the data showed three or more transit, the existence of this planet has not yet been confirmed by follow-up observations; as a result, theres still a small possibility that some candidates are artifacts of something besides already planning that causes the stars to dim

The distribution on large scales is in the form of a filamentary network, dictated by the gravitational instability of the "cold" dark matter

Small initial fluctuations in density get amplified by the fact that high concentrations of mass attract other mass and grow. Galaxies then result from theformation of deep potential wells of dark matter, into which gas falls and eventually forms stars.

How is the Doppler shift relevant to spectral lines?

Spectral lines provide the reference points we use to identify and measure Doppler shifts Ex: if the hydrogen lines from the object appear at longer wavelengths, then we know they are redshifted and the object is moving away from us, and moving toward us with a blueshift.

Understand the local description of the star and how this is related to the celestial co-ordinate system.

Stars near the north celestial pole are circumpolar meaning that they remain perpetually above the horizon, circling around the north celestial pole each day Stars near the south celestial pole never rise above the horizon at all All other stars have daily circles that are partly above the horizon and partly below, which means they appear to rise in the east and set in the west.

Organization of the solar system (including masses and distances from the sun)

Sun: 333,000ME Mercury: 0.055ME, 0.39 AU Venus: 0.8ME, 0.72 AU Earth: 1.00ME, 1 AU Mars: 0.11ME, 1.52AU Asteroid belt: 2.2-3.2AU Jupiter: 318ME, 5.20AU Saturn: 95.2ME, 9.54AU Uranus: 14.5ME, 19.2AU Neptune: 17.1ME, 30.1AU Kuiper Belt: 30-50AU Pluto (dwarf planet): 0.002ME, 39.5 AU Eris: 0.0028ME, 67.7AU Oort Cloud: 5,000-100,000AU

How old is the sun? The universe?

Sun: 4.6 billion years Universe: 14 billion years

Phases of venus

The different variations of lighting seen on the planets surface, similar to lunar phases. This was evidence that supported the heliocentric model because if the earth were the center of the universe Venus would only go through four phases; however, it was observed that Venus went through eight phases, proving that the sun was the center of the universe.

Light year

The distance light travels in a year, used to express astronomical distances (9.5 trillion kilometers)

Escape velocity

The escape velocity from earth's surface is about 40,000 km/h or 11 km/s; this is the minimum velocity required to escape earths gravity for a spacecraft that starts near the surface.

What is the evidence for water in Enceladus

The fountains of water vapor and ice crystals must have some sub service source, and careful measurements of the way on Cletus wobbles on its axis as it orbits Saturn have lead scientist to suspect that I included as a global, sub surface ocean of liquid water.

Know the basic physical characteristics of the planets (rocky/gas) and their atmospheres (thin/thick)

The giant outer planets Jupiter, Saturn, Uranus, and Neptune have extremely thick atmospheres of hydrogen, helium, methane, and ammonia. Gaseous Mercury: rocky,thin Venus: rocky, thick Earth:rocky, thin Mars: rocky, thin Pluto: rocky, thin

Occam's razor

The idea that scientists should prefer the simpler of two models that agree equally well with observations

Laws of conservation

The law of conservation of angular momentum tells us that total angular momentum can never change. an individual object can change is angular momentum only by transferring some angular momentum to or from another object. The law of conservation of energy tells us that, like momentum and angular momentum, energy cannot appear out of nowhere or disappear into nothingness. Objects can gain or lose energy only by exchanging energy with other objects.

The phases of the moon and the physical reasons for them

The lunar phase or phase of the moon is the shape of the illuminated portion of the Moon as seen by an observer Half the moon is always illuminated by the sun, but the amount of this illuminated half that we see from Earth depends on the Moon's position in its orbit.

how stars evolve through the Hertzprung-Russell diagram.

The main sequence stretching from the upper left (hot, luminous stars) to the bottom right (cool, faint stars) dominates the HR diagram. It is here that stars spend about 90% of their lives burning hydrogen into helium in their cores. Main sequence stars have a Morgan-Keenan luminosity class labelled V. red giant and supergiant stars (luminosity classes I through III) occupy the region above the main sequence. They have low surface temperatures and high luminosities which, according to the Stefan-Boltzmann law, means they also have large radii. Stars enter this evolutionary stage once they have exhausted the hydrogen fuel in their cores and have started to burn helium and other heavier elements. white dwarf stars (luminosity class D) are the final evolutionary stage of low to intermediate mass stars, and are found in the bottom left of the HR diagram. These stars are very hot but have low luminosities due to their small size.

What is an eclipse and why is it rare

The moon and earth both cast shadows in sunlight, and these shadows can create eclipses when the sun, earth, and moon fall into a straight line. Eclipses come in two basic types: Lunar eclipse: occurs when Earth lie directly between the sun and the moon, so earth's shadow falls on the moon Solar eclipse: occurs when the moon lies directly between the sun and earth, so the moons shadows falls on earth We see an eclipse only when a full or new moon occurs near one of the points where the moons orbits crosses the ecliptic plane

What is the ecliptic and the Milky Way?

The path the sun follows as it appears to circle around the celestial sphere once each year. It cross the celestial equator at a 23% angle, because of Earth axis tilt. Our view in all directions into the disk of our galaxy. The band of light we call the Milky Way circles all the way around the celestial sphere, passing through more than a dozen constellations.

What are the sources of internal heat for a planet?

The process of differentiation converted additional gravitational potential energy into thermal energy is denser materials sink to the core. The rock and metal that built the terrestrial worlds contain radioactive isotopes of elements. As these radioactive materials decay they release heat directly into the planetary interiors in essence converting some of the mass energy of the radioactive nuclei to thermal energy.

Understand how the expansion history will be determined by the energy balance between kinetic energy and gravitational potential energy

The rate of expansion at any given time represents a form of kinetic energy. The mass of all the constituents of the universe exert a gravitational force, so they have gravitational potential energy. The force of that gravity acts to slow down the expansion, so that the kinetic energy is slowly converted into gravitational potential energy (recall that the total energy is conserved). So, the final outcome will depend on the relative amount of energy in the two reservoirs. If there isn't enough kinetic energy initially, it can get completely absorbed by the potential energy. Then the object falls back to earth (like a baseball thrown up). If there is enough kinetic energy it can get to infinite distance with finite velocity, like a rocket launched into space.

How is the central black hole related to other properties of the host galaxy?

The size of the black hole in a galaxy is correlated with the size of the nuclear bulge of stars. This probably represents the outcome of an early rapid assembly phase of the galaxy, which eventually transitioned to the more gradual star formation process we see in galactic disks.

the solar system inventory: know the planets and their properties. Know where the asteroids and comets reside

The sun; gaseous 99.8% of the solar system mass Mercury; smallest planet, desolate and cratered, extreme temperatures, large iron core Venus; routes backwards, nearly identical in size to earth, hidden by clouds, extreme greenhouse effect Earth; only life, oxygen, ozone, water, first planet with a moon Mars; half earths size, ancient volcanoes, great canyon, once had warm and wet periods, Asteroid belt Jupiter; largest planet, mass 300 times more than earth, Great Red Spot, hydrogen and helium, no solid surface, dozens of moons and faint rings, Saturn; orbit twice as far as Jupiter, second largest, 4 large rings made of tiny particles, numerous moons, river beds shaped by Methane and ethane rather than water Uranus; twice as far as Saturn, methane gives Uranus its pale blue green color, no solid surface, rings, tipped on its side, most extreme seasonal changes Neptune; slightly smaller than Uranus, rings and many moons, triton with geysers of nitrogen gas that orbits backwards, Kuiper belt Pluto; dwarf planet, Kuiper belt, extremely cold and dimly lit, Charon Eris; dwarf planet, larger than Pluto, Kuiper belt Oort Cloud (comets)

Understand the basic sequence of planet formation from small bodies to large, and how this helps to explain rocky planets and gas giants

The terrestrial planets started out as small solid seed of metal and rock in the inner solar system. Then through collisions and combination and electrostatic forces, they began to attract each other through gravity, accelerating their growth into boulders large enough to count as planetesimals. This gave them more surface area to make contact with other planetesimals and more gravity to attract them. But once they reached larger sizes, further growth became difficult. The Jovian planets began as large icy planetesimals which then captured hydrogen and helium gas from the solar nebula. This added gas made their gravity even stronger allowing them to capture even more gas.

What causes the seasons

The tilt of earths axis causes sunlight to fall differently on Earth at different times of year

Two stars can have the same temperature, but vastly different luminosities. How?

The total amount of flux emitted depends not only on the temperature (which determines emission per unit area) but also on the radius of the star (which determines the surface area)

How does the Sun produce its energy? How does this determine the Sun's lifetime?

There are two kinds of nuclear reactions: • Fission: This is when a large atom splits into two smaller ones. This is what the first atom bombs did. • Fusion: This is when two smaller atoms fuse to make a large one. This is what the Sun does (also what Hydrogen bombs do) The source of the energy is that protons are converted into neutrons during these reactions. Neutrons are slightly less massive than Protons and so this mass difference can be converted into energy, as per Einstein's famous equation. In this equation, c is the speed of light, so we can calculate how much energy one gets out. For c=3 x 10 m/s, we see that 1 kg of Hydrogen yields about 10 Joules. It also means about 0.7% of the original Hydrogen mass is converted into energy. • This also gives us a way to calculate how long the Sun can last if it powers itself by this process. Since we know how bright the Sun is, and we know the efficiency of converting mass into energy, we can work out the rate at which the Sun is consuming Hydrogen. We can then ask how long will it take for the Sun to consume all its mass. This gives us an age of about 10 years.

How does temperature relate to thermal energy?

Thermal energy measures the total kinetic energy of all the randomly moving particles in a substance, while temperature measures the average kinetic energy of the particles. Thermal energy depends on temperature, because a higher average kinetic energy for the particles in a substance means a higher total energy.

How do we measure stellar masses?

To do this, we need two stars who are gravitationally bound together - a binary star. About 50% of stars are found in binaries. • We can use Kepler's third law to measure the total mass of the system if we determine the period and the separation or the velocity. If we measure the period P and the semi-major axis a, then we can determine the sum of the two masses. • Without further information, this is as much as we can get. However, if we have spectral lines from both components, we can get the mass ratio between the two. In this event we can measure the individual masses for bothcomponents of the binary

Understand that the first observable phase of the expansion is when atoms first formed, leading to the cosmic microwave background

This is emitted when the temperature was several thousand degrees but has been cooled by the expansion to just a few degrees - When the universe reaches an age of about 380,000 years, and has cooled to about 3000˚K, an important change occurs. At this point, protons and electrons can combine to form atoms and photons are no longer energetic enough to unbind them. The Universe is no longer opaque, because the number of electrons available to scatter photons drops dramatically. After this, photons can travel to our telescopes largely unimpeded by material in between. So, although it was emitted by a gas with temperature of a few thousand degrees, the temperature (which scales with the frequency and so inversely with wavelength) will be decreased by a factor equivalent to the redshift. Thus, the radiation we see today is characterised by a temperature of only a few degrees. The cosmic microwave background (CMB) is electromagnetic radiation left over from an early stage of the universe in Big Bang cosmology. These photons make up the Cosmic Microwave Background.

The photoelectric effect

Under the right circumstances light can be used to push electrons, freeing them from the surface of a solid. The photoelectric effect refers to the emission, or ejection, of electrons from the surface of, generally, a metal in response to incident light. ... That is, the average energy carried by an ejected (photoelectric) electron should increase with the intensity of the incident light.

Understand that this implies a universal expansion, and understand the concept of lookback time and how the age of the Universe is approximately related to the Hubble constant.

Velocity increasing with distance is a generic consequence of expanding universe models Hubble's law means that the further away an object is, the bigger the redshift. This is consistent with what we discussed before about quasars - that their large redshifts indicate substantial distances. If a galaxy is a billion light years away, it took a billion light years for the light to reach us - this is defined as the lookback time. So, further we look into the universe, the farther back in time we see. There is a limit - when the light travel time equals the age of the universe, this is the cosmological horizon This is not a physical limit - the universe extends beyond this, but we cannot probe it observationally. Light hasn't had enough time to reach us from this distance. The Hubble constant H tells us how fast the galaxies are moving apart from one another. The units (km/s/Mpc) are equivalent to an inverse time, so that the inverse of H tells us something about the time it has taken to expand to the current scale. So, if the expansion were constant, the age of the universe would be roughly 1/H. So, if we take our current estimate of 70 km/s/Mpc, we get a timescale of 1/H = 14 billion years.

the names for the different parts of the electromagnetic spectrum and what distinguishes one from another (don't need the numbers, just the reason)

Visible light has wavelengths ranging from 400nm at the blue or violet end of the rainbow to about 700nm at the red end. Light with wavelength somewhat longer than red light is called infrared because it lies beyond the red end of the rainbow Radio waves are the longest wavelength light The region near the border between infrared and radio waves where wavelengths range for micrometers to centimeters is often called microwaves Light with wavelength somewhat shorter than blue light is called ultraviolet because it lies on the blue end of the rainbow But with even shorter wavelengths is called x-rays. The shortest wavelength light is called gamma rays

Relative size scales of the solar system

Voyage model: Sun is grapefruit Jupiter is a marble Earth is the ballpoint of a pen (orbiting the sun at a distance of 15m) Moon is 4 centimeters from Earth

What are we infering when we measure the redshift-distance relation with supernovae?

We actually infer an accelerating universe. Redshift is a measure of how much the universe has expanded between the emission of that photon and its detection today. What this means is that, for a given redshift, the supernovae appear fainter than they should even for open universes with very little mass. For higher mass densities, the supernovae should be closer than they actually are.

What sort of information can we get with this method and what are the selection effects/biases that result from using this method.

We can learn the planets approximate mass, we can learn the center of mass for the star system, the orbital period and therefore surface temperature. RV method is biased towards finding the most massive exoplanets. Also best suited for identifying planets that orbit relatively close to their star, because being closer means a stronger gravitational tug and hits a greater velocity for the star as it orbits the system center of mass. Shorter Orbits also allow easier confirmation of the planets existence, because it is easier to record multiple repeats of the Doppler curve.

Understand the implication - requires a new form of matter, "dark energy" that provides additional pressure to drive expansion

We have a mass census which suggested a density about 30% of the critical density. This predicts what the distribution of distance versus redshift should be, and we observe the supernovae to be fainter (more distant) than anticipated. This implies the universe is subject to an additional force that is causing it to accelerate. We term this "Dark Energy".

Understand how the cooling of Mars ultimately resulted in the loss of the Atmosphere

When mars had a warmer core which generated stronger magnetic field the warmer interior caused extensive volcanism and out gassing. The stronger magnetosphere protected atmosphere from solar wind in this atmosphere was created by the outgassing and volcanism. However, the lack of core convection meant no global magnetic field. The weaker magnetosphere has allowed solar wind to strip away much of the atmosphere.

What is the definition of a planet?

a celestial body distinguished from the fixed stars by having an apparent motion of its own (including the moon and sun), especially with reference to its supposed influence on people and events. It is in orbit around the Sun. It has sufficient mass to assume hydrostatic equilibrium (a nearly round shape). It has "cleared the neighborhood" around its orbit.

Magnitude scale

a logarithmic measurement scale, 5 times the logarithm of the flux recieved Logarithms work by counting factors of 10. The stars with the greatest apparent brightness in the sky are first magnitude. A star that is 100 times fainter is fifth magnitude.

Visual Binary

a pair of stars that we can see distinctly (with a telescope) as the stars orbit each others. Sometimes we observe a star slowly shifting position in the sky as if it were a member of a visula binary, but its companion is too dim to be seen

What is an ellipse? How is it described by the parameter eccentricity?

a regular oval shape, traced by a point moving in a plane so that the sum of its distances from two other points (the foci) is constant, or resulting when a cone is cut by an oblique plane that does not intersect the base By altering the distance between the two foci while keeping the length of string the same, you can draw ellipses of carrying eccentricity, a quantity that describes how much an ellipse is stretch out compared to a perfect circle.

Temperatures range from?

about 3000˚K for 0.08 solar mass stars, to 50,000˚K for 100 solar mass stars.

Greek geocentric model?

astronomy, the geocentric model (also known as geocentrism, or the Ptolemaic system) is a superseded description of the universe with Earth at the center. Under the geocentric model, the Sun, Moon, stars, and planets all orbited Earth

How can astronomers measure surface temperature fairly precisely ?

by comparing a star's apparent brightness in two different colors of light

Stellar spectral type & accronym

classifying stars according to surface temperature by assigning a spectral type determined from the spectral lines present in a star's spectrum OBAFGKM

Hotter objects emit a __________ _________ of their total light at ________ wavelengths

greater fraction; shorter

galaxies are often found in?

groups and clusters

Apparent magnitude

how bright a star appears in the sky.

Spectroscopic binary

identifies through observations of doppler shifts in its spectral lines. If one star is orbiting another, it periodically moves towards us and away from us in its orbit, which means its spectral lines will show alternating bluieshifts and reshifts

How can we use Kepler's third law to measure the total mass of the system ?

if we determine the period and the separation or the velocity.

Diffusion

is the term for a disorganised motion in which each step has no memory about the previous step. In the case of the sun, photons get scattered in random directions as they move through the Sun. To get from the center to the surface by this process is slow - about 100,000 years.

giants

somewhat smaller in radius and lower in luminosity (but still much larger and brighter than main-sequence stars of the same spectral type)

Absolute magnitude

the apparent magnitude it would have if it were at a distance of 10 parasecs from earth.

Main sequence stars

the prominent streak running from the upper left to the lower right on the H-R diagram. Normal hydrogen burning stars

stellar parallax

the small annual shifts in a star's apparent position caused by Earth's motion around the sun

What is the spectrum of star/planet and how can we use it to tell the chemical composition of the atmosphere? How does it show the temperature of a planet?

the spectra that we see coming from stars often contain what look like dark lines at particular colors, which means there is much less light coming from the star at that color than at the nearby colors. This usually means that the star's atmosphere contains certain types of molecules which absorb light of that color, so we don't see as much of it coming from the star. Astronomers can use the information from these "spectral lines" to figure out what a star is made of. Because the randomly bouncing photons interact so many times with those Atoms or molecules, they end up with energy levels that match the kinetic energies of the objects' atoms or molecules which means the photon energies depends only on objects temperature, regardless of what object is made of.

White dwarfs

the stars near the lower left are small in raidus and appear white in color because of their high temperatures.

What do small anisotropies observed indicate?

the start of galaxy formation and are thought to represent quantum fluctuations amplified by an early rapid period of expansion

Luminosity

the total amount of power that a star emits into space

Globular Cluster

up to a million stars in a dense ball bound together by gravity

Supergiants

very large in addition to being very bright

Understand how a black hole is defined by its event horizon, and that this can be understood as a warping of space.

• If a neutron star gets too massive and cannot be supported by neutron degeneracy pressure, then it will collapse to such high density that it leaves behind a black hole This edge is called the "event horizon", and it is the last location from which light can escape. Note however, this is not a surface in the normal sense. An atom falling into the black hole will cross the event horizon without encountering anything = different. The only change is that we will no longer see any light emitted by that atom. • Mass causes space-time to warp, and gravity is the consequence of motion caused by this warp. When the warp gets extreme enough, this is when we get a black hole. At large distances from even a black hole, the warp is weak enough that it is littledifferent from that of a regular star of similar mass. It is only when you get close to the event horizon that the relativistic effects become important.

Know the three classes of galaxies and their basic structures.

- Spiral galaxies possess both a disk component and a "spheroidal" component (the nuclear bulge and the halo) The disk contains an interstellar medium of gas and dust, from which stars form. - Elliptical galaxies: show only a spheroidal component (no disk) They have little gas or new star formation, i.e. they are composed only of old stars (no O or B stars). This means they have red colours compared to the relatively white colours of spirals. Measurement of the internal stellar velocities demonstrate that the stellar motions are randomly oriented, i.e. no evidence for disk-like rotation. - Irregular Galaxy: This is a catch-all term for those that do not fall neatly into the spiral or elliptical classification. Show evidence of gas and dust, with ongoing star formation. At the present day, they're smaller on average (e.g. the Magellanic cloud satellites of the Milky Way are of this type) Earlier in the Universe's history, a lot of galaxies fall into this class, including larger ones.

Understand the consequences of this warping, such as gravitational lensing, time dilation and redshift of photons.

- Stretching of spacetime increases the distance light has to travel. - Since the speed of light is constant, this results in a stretching of the wavelength and a lowering of the frequency - This is termed the gravitational redshift. Spectral lines emitted by atoms close to a neutron star or black hole will appear at longer wavelengths when observed by someone much farther away - Time Dialtion: The stretching of spacetime also results in a slowing down of time as measured by the instruments near a black hole. This means that, when observed from afar, time appears to be moving more slowly close to the black hole. Gravitational lensing: A giant black hole spouting energy from inside a galaxy is acting like a cosmic magnifying glass, giving astronomers a clear view of an even more distant galaxy behind it. According to the theory, very large masses warp the space-time around them, even causing light to bend as it travels through the region. Thus, light from faraway objects sometimes can be magnified by the bent space-time to provide a larger and brighter, though also distorted and curved view

How is the solar corona related to sunspots?

- Sunspots are parts of the solar surface that are cooler than the rest. This is why they appear darker. They are regions of high magnetic field, which exerts a strong pressure, preventing hotter gas from rising from below, allowing that region to cool. The number of Sunspots on the Sun at any one time can be counted -During solar min periods, the corona has a fairly simple structure which extends outward from the low latitude regions near the Sun's equator. From our viewpoint on Earth, the corona looks a bit like a pair of wings extending outward on either side of the Sun. -When the Sun is very magnetically active and disturbed and there are lots of sunspots, the corona looks much different. The appearance of the corona at solar max reflects the complex and chaotic state of the Sun's magnetic field. Photos of the corona at solar max show dense regions called streamers bursting forth in a haphazard fashion from all latitudes on the Sun.

Understand what happens when a star runs out of Hydrogen, and how it proceeds through the subsequent nuclear burning stages.

1. Over time, Hydrogen is burnt up, so the amount of Helium increases. Eventually, there is no Hydrogen left to burn in the core; it is all Helium. This means there is no more heat source and the core must contract again to provide sufficient heat to maintain pressure. 2. As the core contracts, so do the overlying layers of Hydrogen. These heat up and start nuclear fusion in a shell, surrounding the core. As the core contracts, and the star begins to burn Hydrogen in a shell, the stars envelope begins to expand, and the surface temperature goes down. 3. The star first becomes a "subgiant" and then a "red giant". At this stage it can be 10-100 times the radius of the Sun on the main sequence. 4. As the star becomes a giant star, the core continues to contract (and grow, since the shell is adding Helium to it). What happens next depends on the mass. For low mass stars like the Sun, the core gets so dense that electron degeneracy pressure becomes important in supporting it against gravity. 5. Eventually, the contraction reaches high enough densities and temperatures that the star can start to burn Helium in nuclea fusion reactions - this is a new source of energy.

What are brown dwarfs, and how does degeneracy pressure help to support them?

A brown dwarf is a gravitationally bound gas object with mass less than 0.08 solar masses. Radiates mostly infrared light because surface temperatures are less than 2000˚K. It has thermal heat from the gravitational collapse, but it is too small to generate heat from fusion. These are "failed stars", and are intermediate between stars and planets (which have to orbit a star). Brown dwarfs settle into a stable configuration by balancing the force of gravity with a new source of pressure - electron degeneracy pressure. In matter at very high densities, the interactions between particles become strong enough that the material has energy levels in the same way individual atoms do. If every spot in an energy level is filled by particles, the material cannot contract any further - this provides a source of pressure that balances the gravity causing the brown dwarf to contract.

the model for formation of the Moon and how this relates to differentiation within the Earth

A mars sized object struck earth At a speed and angle that blasted earths outer layers into space. according to computer simulations, this material could've collected into orbit around our planet, and accretion within this ring of the breeze could've won the moon. Evidence. The moons overall composition is quite similar to that of earths outer layers just as we should expect if it were made for material blast away from those layers. Also, the moon has a much smaller proportion of easily vaporize ingredients such as water than earth. this fact supports the hypothesis because the heat of the impact of a prize these ingredients.

Understand the properties of neutron stars and how they are related to pulsars. Why does the spinning, magnetised object have to be a neutron star?

A neutron star is the remnant left behind by a core collapse supernova - An observational manifestation of neutron stars is pulsars. These are identified as radio sources with a strongly periodic signal. The range of pulse periods found in pulsars ranges from milliseconds to tens of seconds. A physical object like a star is limited in how fast it can spin. If the rotational speed at the surface of a star is larger than the escape velocity, then material at the surface will fly off. White dwarfs cannot spin faster than about once every few seconds, and there are many pulsars with sub-second spin periods. Only a neutron star has a strong enough gravity and is compact enough to spin this fast.

the different kinds of force

Applied Force. Gravitational Force. Normal Force. Frictional Force. Air Resistance Force. Tension Force. Spring Force.

Why do comets have tails?

As a comet approaches the Sun, it starts to heat up. The ice transforms directly from a solid to a vapor, releasing the dust particles embedded inside. Sunlight and the stream of charged particles flowing from the Sun - the solar wind - sweeps the evaporated material and dust back in a long tail.

Understand how the method for finding extrasolar planets by radial velocity variations works

Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in the spectrum of the planet's parent star. The other method of searching for gravitational tugs do to orbiting planets is the Doppler method, which searches for a stars orbital movement around the center of mass by looking for changing Doppler shifts in its spectrum

Understand how the observations of Mars indicate that liquid water may once have existed on the surface.

Dried up river beds and other geological features show that water flowed on Mars in the distant past, notice the indistinct rims of many large craters in the relative lack of small crate it was both fax argue for ancient rainfall, which would've eroded crater rims and erased small critters all together. Mineral evidence such as Hemetite and jarosite suggest formation in a salty environment such as a pond or lake. Curiosity found clumps of pebbles with Rounded surfaces in sedimentary layers clearly indicate formation and flowing water.

How does wind mass loss lead to a white dwarf?

If the star is massive enough it can eventually start to burn Carbon, but stars are also losing mass from their outer regions in winds at this stage of evolution, and they may lose enough mass to prevent ignition of Carbon in the core. Stars with initial masses less than about 8 solar masses will eventually become white dwarfs. - When the core reaches a size approximately equal to that of the Earth (about 100 times smaller than its original size when it was fusing hydrogen), the collapse will stop. It will simply cool off slowly by radiating light, getting fainter and fainter until it no longer gives off enough light to be visible. While the object is still visible, it is called a white dwarf

Understand the dynamical argument about why the galaxy is dominated by dark matter.

Inside the orbit of the Sun (8 kiloparsec radius) the mass enclosed is about 90 billion solar masses. Within the orbit of a distant star (at about 30 kiloparsec radius), the enclosed mass is more than 500 billion solar masses. If we count up all the mass we can see in gas and stars, we only get about 100 billion solar masses in total. Thus, most of the matter in the Milky Way does not radiate light. Furthermore, we think it is not even the same kind of material as "baryonic" matter (i.e. made out of protons, neutrons and electrons) On larger scales, more than 80% of matter is this type. Recall that velocity is approximately constant as a function of radius in the outer parts, which tells us that the total mass enclosed by that radius increases linearly with radius • This is very different from the distribution of luminous stars. Most of the stars and gas we observe lie well inside the Sun's location, but the velocity is measured to be flat well outside this. We therefore infer there is a lot of mass in the Milky Way that does not give off light. These are also galaxies, but much smaller than the Milky Way or Andromeda. • We can also use their motions to constrain the mass of the Milky Way further, because they are much more distant than the Milky Way stars and so probe the mass at larger radii.

Coepernican heliocentric model

It positioned the Sun near the center of the Universe, motionless, with Earth and the other planets orbiting around it in circular paths modified by epicycles and at uniform speeds.

What is the Kepler satellite?

Kepler is a space observatory launched by NASA to discover Earth-size planets orbiting other stars

Scientific method

Make observations, ask a question, suggest a hypothesis, make a prediction, perform the test: experiment or additional observation. Test supports hypothesis; make additional predictions and test them Test does not support hypothesis; revise hypothesis or make a new one

What is the lifetime of these active phases?

Mass must fall in at the rate of 1-10 solar masses per year to explain the luminosities • Observations suggest that quasars last for tens to hundreds of millions of years, so that they should grow to millions to billions of solar masses if they accrete at these rates • This is consistent with the velocities inferred from the broadening of the spectral lines.

How do we constrain the mass, size and luminosities of the active regions?

Mass: gas motions indicate masses in the millions to billions of solar masses, If we take the velocities we infer from the broadening and the scales we infer from the variability, we can calculate the mass contained within the emission region, and it is estimated to be in the billions of solar masses Size: Variability on timescales of hours, which limits the size to the light travel distance on this timescale, roughly 10 AU or less. • Their physical sizes are small - less than one light year across. We can estimate this by their variability, by calculating the distance light can travel on such timescales. Luminosity: This mass, confined to this small region, still manages to put out more than 10-1000 times the luminosity of the rest of the galaxy. The fact that they are detectable as star-like objects despite being at great distances implies huge luminosities

How do we determine the age of a star cluster?

Massive stars consume their fuel the fastest, and the smallest stars the slowest.Therefore, for a cluster of given age, some stars (those whose main sequence lifetimes are shorter than the cluster age) will be absent from the HR diagram. • Alternatively, we can determine the age of the cluster by determining the mass of the largest main sequence mass remaining in the cluster.

Understand the idea of Migration and how this helps to explain these close-in planets

Migration may be caused by waves passing through a gaseous disc. The gravity of a planet moving through a disk can create waves that propagate through the desk, causing material to bunch up as the waves pass by. This bunched up matter then exerts a gravitational pull on the planet that tends to produce its orbital energy, causing the planet to migrate inward toward it star. This helps to explain close in planets because some planets are very similar to Jovian planets however they're very close to the stars and it is possible that they went through this planetary migration before the end of the formation of the star system.

Large fractions of _____have some kind of _____around them

Stars, planets

Stellar parallax effect

Stellar parallax is parallax on an interstellar scale: the apparent shift of position of any nearby star (or other object) against the background of distant objects.

Understand the compositions of the giant planets and the interior structure

The Jovian planets are made mostly of hydrogen, helium, and hydrogen compounds, and differ primarily in the relative proportions of hydrogen compounds. The cores of all four jovian planets are made of some combination of rock, metal and hydrogen compounds. Jupiter and Saturn have similar interiors, with layers extending outward of metallic hydrogen, liquid hydrogen, gaseous hydrogen, and topped with a layer of visible clouds. Unlike Jupiter and Saturn, Uranus and Neptune have cores of rock and metal, but also water, methane and ammonia. The layer surrounding the core is made of gaseous hydrogen, covered with a layer of visible clouds similar to Jupiter's and Saturn's.

What is the Milky Way? Understand how redenning and extinction make it hard to observe in the galactic plane.

The Milky Way is the name we adopt for our own Galaxy. It refers to the appearance of the disk of stars and how they appear on the sky. The space between the stars is not completely empty. There is a low density of gas and dust (large molecules) spread throughout the Galaxy. Light from distant stars must pass through this gas and the dust absorbs some of the light, making the stars appear fainter and redder. This makes it hard to see all the way across the Galaxy. In astronomy, extinction is the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and the observer.

What is the solar wind? How does it affect Earth and other planets?

The Sun's outer atmosphere, the super-hot corona, is the source of the solar wind, a steady outflow of charged particles from the Sun. The solar wind is a stream of energized, charged particles, primarily electrons and protons, flowing outward from the Sun, through the solar system at speeds as high as 900 km/s and at a temperature of 1 million degrees (Celsius). It is made of plasma. The surface of the Sun rotates and magnetic fields can get twisted and wound up by this rotation. They can undergo sudden changes if they get too twisted. Broken magnetic field lines can release bursts of plasma that give rise to solar flares, bursts of high energy particles and X-rays. It affects it by the intense clouds of high energy particles that it often contains which are produced by solar storms. When these clouds, called coronal mass ejections, make their way to the Earth in 3-4 days, they collide with the magnetic field of the Earth and cause it to change its shape. This can lead to auroas when the CEM's break through Earth's magnetic field.It can also affect a planet's atmospher greatly.

Mass Momentum Angular momentum Force

The amount of matter in your body In objects momentum is the product of its mass and its velocity. Momentum use to describe objects turning in circles or going around curves The only way to change in objects momentum

Apparent Brightness

The amount of power (energy per second) reaching us per unit area

What is the composition of the Earth's atmosphere and how does this regulate the greenhouse effect? What happened to the atmosphere of Venus?

The atmosphere is a mix of gases; it's overall composition is approximately 77% nitrogen and 21% oxygen, with small amounts of argon, water vapor, carbon dioxide, and other gases. Visible light passes through the atmosphere. Some visible light is reflected by clouds, haze, and the surface. The surface absorbs visible light in the mid sternal radiation and infrared. Greenhouse gases absorb and emit infrared radiation, there by heating the lower atmosphere. The greenhouse effect occurs when the atmosphere temporarily trap some of this infrared light, slowing its return to space. Venus is the carbon dioxide atmosphere created extremely strong greenhouse effect that makes Venus very hot. Venus must have somehow lost its outgassed water. Without oceans, carbon dioxide cannot dissolve or become locked away in carbonate rocks.

Why do we think there is a black hole in the Galactic center?

The center can be defined both by the peak of infrared emission or by the point about which the disk rotates. By imaging the location of the peak of the light, Astronomers identified a strong radio source, called Sagittarius A*. Using the elliptical orbits and Kepler's laws, one can infer the mass of the central object. This is inferred to be about 4 million solar masses. This mass is confined to be within a region approximately the size of the solar system. No star cluster this compact could be stable, so we infer that it has to be a black hole.

Why are globular clusters better?

The clusters are better tools for studying Galactic structure because they are brighter and not restricted to a narrow band on the sky. Clusters are much brighter than individual stars, so they can be seen to much greater distances.

Understand the mass range of stars and how this is related to their spectral classification, their temperatures, luminosities and lifetimes.

The largest stars are about 100 times the mass of the Sun. These are hot, with surface temperatures of 50,000˚K or so. The smallest stars are about 0.08 times the mass of the Sun. They are cool, with temperatures about 3000˚K - Just as we did with the Sun, if we know the mass of a star and the luminosity, we can use the known efficiency of the nuclear fusion process to calculate the rate at which the star is consuming itself, and hence the lifetime. - For a massive star, say 10 solar masses, the luminosity is 10,000 times higher than the Sun, so it is eating itself up 1000 times faster. Thus, massive stars live for only a short period of time. In this case about 10 million years. - On the other hand, low mass stars are fainter. A 0.1 solar mass star has a luminosity of 1% that of the Sun, so it lasts 10 times longer. - Massive, hot stars appear bluer and cooler, lower mass stars appear red.

What is the nebular theory and what observations support it?

The nebular theory holds that our solar system form from the gravitational collapse of a great cloud of gas 1. All the planets orbit the Sun in the same direction. Most of their moons also orbit in that direction, and the planets (and the Sun) rotate in the same direction. This would be expected if they all formed from a disk of debris around the proto-Sun. 2. The planets also have the right characteristics to have formed from a disk of mainly hydrogen around a young, hot Sun. Those planets near the Sun have very little hydrogen in them as the disk would have been too hot for it to condense when they formed. Planets further out are mostly hydrogen, (since that was what was mostly in the disk), and are much more massive because there was so much more material they could be made from. Finally in this model the Sun is mostly composed of hydrogen. This can also be tested. Observations of the Sun agree incredibly well with what would be expected of a giant ball of mostly hydrogen generating heat by nuclear fusion in the core. The composition can also be measured using helioseismology (the study of 'Sunquakes') and agrees with the theory.

What is the rotation of these giant planets?

The rotation period we measure in this way is 9 hours 56 minutes, which gives Jupiter the shortest "day" of any planet. In the same way, we can measure that the underlying rotation period of Saturn is 10 hours 40 minutes. Uranus and Neptune have slightly longer rotation periods of about 17 hours, also determined from the rotation of their magnetic fields.

Understand the basic model of accretion onto a central black hole that is believed to be the source of the observed power.

The standard model we adopt to describe all of these phenomena is accretion of gas onto a massive black hole in the center of the Galaxy. This suggests that many, if not most, galaxies possess a black hole in their centers, just as the Milky Way does. The gas orbiting a black hole will lose energy through friction within the gas, radiating energy and moving inwards towards the center. Eventually this mass crosses the event horizon and is lost from sight. The process of moving inwards converts a lot of gravitational potential energy into kinetic energy and then into radiation. It is this radiation that is observed coming from AGN. The orbital speeds of the gas this close to the black hole are also high enough to be able to explain the broadening of the spectral lines. The narrower spectral lines seen in spectra are therefore inferred to come from further out and the broader ones from further in. • These are also high ionization lines because the high radiation environment can ionize gas that would be more weakly ionized under more normal galactic conditions.

How do we measure stellar radius?

The surface area of a star is directly related to the square of its radius. By observing the doppler shifts we can use the bianary star system to measure mass and radius of stars A star's luminosity, or total power given off, is related to two of its properties: its temperature and surface area. If two stars have the same surface area, the hotter one will give off more radiation. If two stars have the same temperature, the one with more surface area will give off more radiation. • For edge-on binaries, we can measure the dip in flux when one goes in front of the other. From the interval between eclipses, we get the period. The size of the dips also yield the stellar radius.

Understand the idea behind the distance ladder, and how different rungs operate (parallaxes, main sequence fitting, cepheids, Tully Fisher relation, supernovae)

There is no one method that works for objects of all distances - some work better for close objects and some for more distance objects • We use the fact that the regions of applicability usually overlap for different techniques, so we can use one to calibrate the other. In this way we map out a "distance ladder", using well understood methods for measuring close distances to calibrate less secure methods at larger distances. For the closest objects, we start with parallaxes. To get a parallax you have to be able to measure the change in angular position of a star over the course of a year. The farther away the star is, the smaller is the angular wobble. Main Sequence Fitting We can also use the common properties of stars of the same type. If we know two stars are of the same mass and evolutionary stage, then their different apparent brightness must reflect their different distances. This is especially useful for stellar clusters, where we can readily identify the main sequence, which should lie at the same part of the colourmagnitude diagram. One useful class is Cepheid Variable stars, which are very bright (can be observed out to 30 Megaparsecs). They are pulsating stars, whose brightness varies with a period ranging from one to a few hundred days. Even more useful is the fact that the period of pulsation is proportional to the instrinsic luminosity! This property makes Cepheid stars a kind of standard candle that we are seeking. We can measure the variations in brightness over a span of time and thereby determine the period of pulsation. Then, knowing the calibrated relation between pulsation period and luminosity, we can determine the intrinsic luminosity. If we also measure then the apparent brightness (the flux reaching Earth), we can determine the distance because F = L/4πd 2 The supernovae that result from the collapse of white dwarfs in accreting binaries (Type Ia Supernovae) are also used as a distance indicator. One advantage is that they are very bright, so they can be seen at great distances. The advantage of these supernovae is that they can be calibrated - luminosity correlates with the rate of decline of the light curve. The decline of the light curve is measured and therefore the peak luminosity can be predicted, and so the distance can be measured by the apparent brightness at the peak.

Understand that the constraints on baryonic matter restrict how much there can be, which implies it is likely to be non-baryonic in nature.

We can rule out essentially all forms of baryonic matter as sufficient to form the dark matter, regardless of the mass range. Either it would produce too much light, too many metals, too many microlensing events, or wouldn't survive long enough (e.g. snowballs) When a MACHO passes between the observer and a distant star, it will gravitational lens the starlight and cause the star to brighten briefly

Understand how we can infer a galaxy's star formation history by looking at the spectral lines of stars of different types and of gas.

We can study the star formation history of a galaxy by examining the spectra. A galaxy spectrum is the sum of the spectra of all the constituent stars and gas. So, we examine the strengths of spectral lines coming from young stars and old stars alike. The relative strengths can tell us the proportion of stars of different age in the Galaxy - essentially a record of the history of star formation.

Understand how cosmological redshifts change the appearance of a galaxy.

We observe the Universe to be expanding, which leads to distant galaxies having a velocity moving away from us. The magnitude of the speed increases with distance, this is Hubble's law. Recall that the Doppler shift implies a shift of the observed wavelength of a spectral line depending on velocity. This means that the wavelengths of more distant galaxies are shifted systematically redder - this is the cosmological redshift. The universe is expanding, so more distant galaxies are moving with greater velocities away from us. This is expressed as redshift z. A higher value for z means that we are seeing objects earlier in the Universe's history

What does expansion imply about the Big Bang?

an early compact phase (Big Bang) when temperatures and densities were higher This predicts the universe was much denser and hotter at early times and so we need to understand the behaviour of matter under these conditions. This is why there is a lot of possible WIMP dark matter candidates. The conditions achieved during the big bang are much more energetic than anything we can achieve in the laboratory or even in the centers of stars. So this probes the regime of high energy particle theory, where our understanding is still limited.

Complete stellar classification: lumonisity class & spectral type

lumonisity class: which is a measure of the stellar radius • I = supergiant • II = bright giant • III = giant • IV = subgiant • V = main sequence The Sun = G2 V, Sirius A = A1 V, Proxima Cen = M5.5 V spectral type; designated by one of the letter OBAFGKM, tells us its surface temperature and color. O stars are the hottest and bluest, white M stars the coolest and reddest

Basic structure of the sun

photosphere: The photosphere is the part of the Sun we actually see directly. (The photosphere is the lowest layer of the solar atmosphere. It is essentially the solar "surface" that we see when we look at the Sun in "white" [i.e. regular, or visible] light.) - It is not a physical surface, because the Sun is a gas ball. - It is rather the location from which photons have a decent chance of escaping unhindered. convective surface: Below the photosphere, the transport of energy is by convection. (Hot dense turbulent gas - This means parcels of hot gas rising and parcels of cold gas falling - like boiling water (granulation appearance) - This pattern of rising and falling parcels of gas results in a network of bright and dark regions - energy transported upwards by rising hot gas - The outer 30% of the solar radius is convective Radiative core: Energy transport in the center of the Sun is by radiative diffusion, rather than convection. This is what happens to the hydrogen gas in the core of the Sun. It gets squeezed together so tightly that four hydrogen nuclei combine to form one helium atom. This is called nuclear fusion. In the process some of the mass of the hydrogen atoms is converted into energy in the form of light. Basically, in the radiative zone, energy generated by nuclear fusion in the core moves outward as electromagnetic radiation. In other words, the energy is conveyed by photons. chemical composition: The Sun is a huge, glowing sphere of hot gas. Most of this gas is hydrogen (about 70%) and helium (about 28%). Carbon, nitrogen and oxygen make up 1.5% and the other 0.5% is made up of small amounts of many other elements such as neon, iron, silicon, magnesium and sulfur.

What are the advantages of putting telescopes in space?

putting telescopes in space can alleviate the atmospheres turbulence It allows us to observe light that does not penetrate Earths atmosphere

Spectra change with ________________ and this determines the ________ ______________ ___ _____.

temperature; spectral classification of stars The absorption and emission lines from different atoms get stronger and weaker as temperature changes. Stars are classified into types depending on the kinds of spectral lines observed, which changes with temperature.

Understand how we calculate cosmological redshifts, and how this is related to velocity for nearby galaxies.

• If the atom is moving towards you, the wavelength is shifted to smaller values - a blueshift. If the atom is moving away from you, the wavelength is shifted to larger values - a redshift. When we take spectra of nearby galaxies, we see a variety of spectral lines from Hydrogen, Oxygen, Carbon, Calcium etc, and we can measure their wavelengths and infer a relative velocity. When we do this we find that nearby galaxies are systematically redshifted - i.e. most of them are moving away from us. We express the reshift as z = (λ' - λ )/λ = v/c, where v is the relative velocity.

Understand what we mean by the critical density, and how we go about measuring the local density of mass relative to this. Know that there appears to be only about 30% of the critical density in normal and dark matter.

• Measurements of the current rate of the expansion tell us what the kinetic energy is today in the Universe's expansion. Thus, we need a comprehensive census of the mass that exists in the universe today and whether the resulting gravitational potential energy is sufficient to slow the expansion to a stop. We usually express this relative to the - "critical density", which is the average density of mass in the universe that would result in the intermediate case where the expansion slows to a stop at infinity. So, based on the known value of the Hubble constant, we know how much mass there needs to be in the Universe today in order to eventually slow the expansion to a halt. How does this compare to the mass there actually is? If we count up all the mass in stars in all the galaxies, it amounts to only about 1% of the required mass. There is also a lot of gas - in cold gas in Galactic disks, in the molecular clouds that make stars, there is also hot gas in galaxy clusters that was ejected by supernovae, and there is gas spread out between the galaxies (recall the forest of absorption lines in distant quasar spectra). When we add up all of this (stars + gas) we still find that the average density of normal matter is only about 4-5% of the critical value.

How does gas get circulated from the disk to stars and back again? What does this do to the composition of the gas?

• Over the course of the 10 billion years of the Milky Way's existence, a lot of the gas has been recycled multiple times between the interstellar medium and stars • Gas is swept up into clouds which collapse to form stars. The stars then evolve through their nuclear burning histories, producing a lot of heavier elements. When the stars die, they lose a lot of their mass either in winds or supernova ejections. This metal-enriched gas is then mixed with the gas in the interstellar medium to begin the cycle again. As a result, the amount of heavy elements in the gas goes up over time and the heavy element fraction is higher in young stars than old stars.

What is the Tuning Form diagram?

• We classify large galaxies (ellipticals and spirals) according to the Hubble tuning fork diagram, which splits the spirals into two classes, depending on whether there is a bar or not.

Understand how we related redshift to the size of the universe at the time of photon emission.

• We express the redshift as z = (λ' - λ0 )/λ0. In the local universe, we can approximate this as Z proportional to the velocity with which galaxies are moving away from us. Another way to think about the redshift is that it relates the size of the universe now to the size of the universe at the time the photon was emitted. • So, λ'/ λ0 = R/R0 where R is the current length scale of the Universe and R0 is the same length scale at the time the photon was emitted. We can determine R and R0 by measuring the distance between two physical objects (e.g. two galaxies) and seeing how it changes with time. • So, we can turn these definitions into an expression that says 1 + z = R/R0. This means that the redshift tells us how much the Universe has expanded since the photon was emitted.