PHYS 20083 - Summer 2003 Complete Study Guide

Physics 20083 - Complete Study Guide

(1): Be able to define wavelength, frequency and photon. Given the relationship between frequency, speed and wavelength (the wave equation) and the relationship between photon energy and wavelength, be able to identify regions of long and short wavelength, regions of high and low frequency, and regions of high and low photon energy on a spectral curve (a graph of intensity vs wavelength).
(2): As an object heats up, two things happen to its spectral curve. First, the overall intensity increases as more photons are emitted by the object. Second, the peak wavelength of the spectrum shifts to a shorter wavelength. Explain briefly why each change occurs. Given a continuous radiation spectrum for an object of a certain temperature, be able to identify the spectrum of an object that is slightly warmer or cooler based on these principles.
(3): Another term for the kind of light (electromagnetic radiation) emitted by the sun and most other objects in nature, regardless of their temperature or composition, is "blackbody radiation". Why is it called "blackbody radiation"? (TQ #1)
(4): Based on the reading Cargo Cult Science, imagine your task is to explain to a South Sea islander why planes don't land there anymore even though the islanders are going through the proper motions that have made planes land there in the past. Come up with your own explanation of why this is true in three or four sentences (which, not coincidentally, is about the length of an average exam answer). (TQ #2)
(5): Based on the reading Cargo Cult Science, explain in your own words (2-3 sentences) why Mr. Young's rat-running experiment was a perfect example of the scientific method compared to most other rat-running experiments. (TQ #3)
(6): How do we use the information from question 2 to estimate the temperatures of stars? Why do objects appear more red, then more yellow, then more blue as they get hotter? From a graph of intensity vs wavelength, be able to identify which of two stars appears redder or bluer and which is giving off more blue or red light.
(7): Explain how Ernest Rutherford discovered the nature of the atoms (that it is a dense nucleus surrounded by a diffuse cloud of relatively light weight electrons). This can be found in your book or on the web. (TQ #4)
(8): What are two ways for an electron to move between energy levels? Explain why atoms can only absorb or emit certain specific photon energies (wavelengths). Explain what happens when an atom absorbs or emits a photon.
(9): Under what conditions do we see emission line spectra? Under what conditions do we see absorption line spectra? Describe exactly how an absorption line spectrum is generated.
(10): Explain how we use the principles of atomic emission and absorption to deduce the composition of different elements in clouds of gas, stars, etc.
(11): Based on your reading of Philosophy and the Scientific Method, answer the following: What is the most significant concept that separates scientific and non-scientific theories? The fact that non-scientific ideas can't be disproven means they aren't useful as a basis for a system of knowledge. Why not? What is the problem with relying on irrefutable beliefs? After all, the irrefutable belief might not be wrong. Try to be concise with your answer.(TQ #5)
(12): What are Fraunhofer lines? (TQ #6)
(13): Explain the process of ionization. Given a simple energy level diagram (e.g. "E=0,5,7,13"), be able to answer questions like "List the energies that an electron in this atom can absorb from its position in the lowest energy level." or "List the energies that an electron in this atom can emit from its position in a certain energy level." or "What's the longest/shortest wavelength transition for an electron from its current energy level?"
(14): Know the two rules associated with Doppler shift (redshift/blueshift and radial velocity proportional to shift) and be able to apply them to real examples of spectra. Know the difference between radial and transverse velocity. If I show you a "rest" spectrum and a couple of other comparison spectra, be able to state whether the comparison objects are moving toward or away from us and which one is moving faster.
(15): If star A is 100 light years away and star B is 200 light years away (neither star moving relative to us), will the light from one star be shifted relative to the other (and if so, will the light be blueshifted or redshifted)? Explain your answer. What if star A is moving away from us at 100 meters/sec, and star B is moving away from us at 50 meters/sec? Will both stars appears shifted? One more than the other? Explain. (TQ #7)
(16): Visit http://www.howstuffworks.com/radar-detector.htm and read the article there about how radar and other speed detectors work, then answer the following: In 1-3 sentences, explain in simple terms how a radar detector can measure your car's speed. Similarly, explain what lidar is and how it works. (TQ #8)
(17): State and briefly explain the equation we use to estimate the lifetime of the Sun (based on the total fuel available and the luminosity). Be able to describe a similar example, such as a car ("tank holds 20 gallons, fuel burns at a rate of 4 gallons/hr, how many hours does the fuel last?")
(18): Explain why chemical and gravitational energy were not accepted as viable methods for energy generation in the Sun's core. Explain how fusion reactions work and how they generate energy. Why is fusion considered to be a viable source for energy generation in the Sun?
(19): Explain why both high temperature and high density are needed in order for fusion reactions to take place.
(20): One important aspect of nuclear physics is its application to medicine. Read http://www.radiologyinfo.org/content/petomography.htm, and answer the following: How does Positron Emission Tomography (PET) work? An alternate site is at http://www.triumf.ca/welcome/petscan.html and http://www.kccancercenters.com/PET.html. (TQ #9)
(21): Another important aspect of nuclear physics involves nuclear power and nuclear weapons. Read http://www.howstuffworks.com/nuclear-power.htm, and answer the following: Why does U-235 work well in nuclear power plants while U-238 does not? What is the purpose of control rods in nuclear power plants? List three significant problems with nuclear power plants as a source of energy. (TQ #10)
(22): What is the "solar neutrino problem"? Despite this inconsistency with theory, most scientists still believe that nuclear fusion is the source of energy for the Sun's core. Explain why this theory hasn't been abandoned, as the scientific method suggests it ideally should.
(23): Read the following web site detailing the solar neutrino problem (SNP): http://www.maths.qmw.ac.uk/~lms/research/neutrino.html, and summarize the "physical" and "astrophysical" solutions to the SNP in 1-2 sentences each. (TQ #11)
(24): How is the core of the Sun defined? What is the envelope of the Sun?
(25): Explain what happens in the radiative zone of the Sun. Explain what happens in the convective zone of the Sun. Why is energy transported differently in the convective zone? Why does energy ultimately leave the Sun in the form of light/radiation?
(26): What is the photosphere of the Sun? Explain the concept of limb darkening. What does limb darkening tell us about the temperature structure of the Sun's photosphere?
(27): Suppose the temperature of the photosphere were constant throughout (instead of the current situation in which it is slightly cooler as you look closer to the surface). Would we still experience the limb darkening phenomenon when we look at the Sun? Explain. What if the base of the photosphere were cooler than the upper layers? (TQ #12)
(28): If we were to observe the Sun's corona during a total solar eclipse (the photosphere is completely blocked by the Moon), what sort of spectrum would we see? (emission, absorption, continuous) Explain.
(29): Define ionization species. Explain how different species of ions are used to estimate the temperature of clouds of gas. How do the ionization species of atoms change as one looks further away from the Sun's surface in the corona? What does this tell us about the temperature structure of the corona?
(30): Why are spectral line widths proportional to the temperature of a gas? How do the spectral emission line widths change as one looks further away from the Sun's surface in the corona? What does this tell us about the temperature structure of the corona?
(31): While the Sun's corona has temperatures of millions of degrees, similar to temperatures in the core, no fusion occurs there. Why is this? (TQ #13)
(32): What is coronium? What kinds of atoms is it really made of? Read http://science.nasa.gov/ssl/pad/solar/corona.htm to find the answer. (TQ #14)
(33): What are the four main functions of a telescope we discussed in class. Briefly define each with a simple sentence, and then state how the aperture of the telescope affects each one.
(34): What causes stellar images to appear blurred ("seeing") when we look at them through ground-based telescopes? Briefly explain how adaptive optics works to correct this problem.
(35): What is the difference between a reflecting and a refracting telescope? Why are reflecting telescopes more popular among professional astronomers, at least one reason? Why do astronomers use instruments attached to telescopes to gather light instead of looking through an eyepiece with their eye?
(36): Given the resolution equation, explain why it is that even though radio telescopes have much larger aperture diameters than optical telescopes, the typical resolution achieved when observing with radio telescopes is very poor.
(37): Explain qualitatively how interferometry works to improve the resolution of radio telescopes. Why isn't interferometry practical for most optical telescopes yet?
(38): Explain how to use parallax to determine the distance to a nearby star. Given the parallax equation, be able to answer questions like "For a star at a given distance, if we observe using a longer baseline, explain what will happen to the observed parallax angle. What if the baseline doubles and the star's distance is doubled?"
(39): Given the parallax equation, be able to draw simple diagrams that justify it. For example, be able to show why the parallax angle should increase as the baseline increases or why the parallax angle should decrease as the distance increases. Also, be able to explain why the parallax method is generally limited to the nearest stars.
(40): Know the definitions of apparent and absolute luminosity. Given the inverse square law equation, explain briefly how we use it to estimate the distances to stars.
(41): Describe how you could determine the distance to a star thousands of parsecs away, assuming that star has spectral characteristics identical to our Sun.
(42): Why do we use radio, rather than optical telescopes, to look for protostars (newly forming stars)?
(43): Describe Hans Bethe's primary contribution to Astronomy, for which he later won the Nobel prize.
(44): What role do supernovae play in the origin of life?
(45): What causes a supernova explosion in massive stars?
(46): What is a pulsar? Why are pulsars not always visible from the Earth? How can we deduce the existence of a pulsar indirectly?
(47): Be able to solve simple numerical proportionality problems with the inverse square law, such as "Star B has an absolute luminosity one-half that of star A, and star B is only 30 pc away while star A is 60 pc away. How does the apparent luminosity of star A compare to that of star B?"
(48): Visit the Hipparcos mission web site at http://astro.estec.esa.nl/Hipparcos/ and answer: What was the purpose of the Hipparcos mission? Check out http://astro.estec.esa.nl/Hipparcos/poster.html to help you explain two useful scientific results that came from this mission. 1-2 sentences each.(TQ #15)
(49): Visit the GAIA mission web site at http://astro.estec.esa.nl/SA-general/Projects/GAIA/gaia.html and answer: What is the purpose of the planned GAIA mission? Explain two useful scientific results expected to come from this mission (look on the menu under "Scientific Topics" for details. 1-2 sentences each. (TQ #16)
(50): Explain how atoms like Hydrogen tend to have weaker absorption line strengths at very low temperatures and very high temperatures. If a star has a very weak Hydrogen line, how could we determine whether that is due to a high or a low temperature or just a low abundance of Hydrogen?
(51): Stars are often classified according to their type with letters from A through O. The Sun, for example, is a G-type star. What was the original use of the ABCDEF... system? In other words, what distinguishes a type A from a type B from a type C star? Today, we usually sort stars into the sequence OBAFGKM. What is this sequence based on? Your book's chapter 19 can help you answer this. (TQ #17)
(52): The original stellar classification system was developed and later revised by Annie Cannon. One of her colleagues, Cecilia Payne, made an important discovery about stars. Describe it. (Your book can help, and lots more information can be found on the web with a simple search). (TQ #18)
(53): Explain the difference between line width and line strength. Explain why line strength depends on both the composition (abundance) of an element and why even when the abundance of an element is very high, the line strength might be very weak.
(54): What is the difference between the terms "larger" and "more massive"? Are larger stars necessarily more massive? Explain.
(55): Given the density equation, be able to solve simple numerical proportionality problems such as "Star B has a Radius (size) twice as large as star A. Star B has a mass one-half that of star A. How does the density of star B compare with that of star A?"
(56): Given the equation of absolute luminosity, be able to solve simple numerical proportionality problems such as "Star B has a Radius (size) twice as large as star A. Star B has a surface temperature one-half that of star A. How does the absolute luminosity of star B compare with that of star A?"
(57): Explain why spectral line widths should depend on the density of a gas and the size of a star.
(58): Be able to put together different concepts regarding stellar properties. For example, "Explain how one could use apparent luminosity, line width and peak wavelength for a given star to estimate the distance to that star." or "Could you find the distance to a star just by knowing the apparent luminosity, the peak wavelength and the ionization species in the spectrum? Explain."
(59): Given two spectral emission lines from two stars of the same temperature and mass, be able to state which one probably has a smaller size based on the line width (is the broader-lined star smaller?), and be able to explain your reasoning. If star A is hotter than star B , but the two stars have identical spectral line widths, what can you say about the relative sizes of the two stars? Explain.
(60): Be able to solve proportionality problems that use different concepts, such as: "Suppose two stars have the same apparent luminosity and size (radius), but star A has higher ionization species in its spectrum compared to star B. Which one is probably closer? Explain" and "Suppose two stars are the same distance from the Earth and have the same surface temperature and mass, but star A has broader spectral lines than star B. Which star appears brighter to us on Earth? Explain."
(61): More concept practice: "Suppose star A and B have the same apparent luminosity, mass and temperature, but star A has narrower absorption lines in its spectrum. Which star will appear to have a larger parallax angle measured from Earth?" // "Suppose star A and B have the same peak wavelength in their spectra and the same apparent luminosity and same mass. Star A has a larger parallax angle compared to star B. Which star would you expect to have broader lines?"
(62): Is the temperature of a star always related in the same way to its density? In other words, are hotter stars always more dense? Always less dense? If a star has a higher temperature, must it always have a broader spectral line?
(63): Given an H-R diagram, be able to plot roughly the positions of stars based on properties like size, temperature and absolute luminosity. For example, "Star X has 1/2 the surface temperature of the Sun but 20 times the radius. Plot (roughly) where this star would fall on the H-R diagram relative to the Sun's position."
(64): When astronomers observe binary star systems edge-on, the spectral line fingerprints of the system sometimes seem to split, then merge, then split, then merge, etc. If I show you an edge-on view of a tilted or edge-on system, be able to explain at each point in the orbit of the companion whether the spectral lines would be merged or split and why.
(65): Would the spectral lines split and merge in a face-on system (where the orbital plane is perpendicular to your line of sight)? Explain. (TQ #19)
(66): How do we use the spectral line shifts in a binary system to determine the orbital velocity? How does the orbital velocity of the companion relate to the shift of its spectral lines? If the system is tilted, how does the measured radial velocity compare to the true orbital velocity of the system? Explain your answer.
(67): Explain how we determine the period for the orbit of the companion star. Given the equation of orbital velocity and the period equation, explain how we use the period and the spectral line shifts to estimate the mass of the central star in an edge-on binary system.
(68): Given the two orbit equations, be able to answer simple proportionality questions such as: "Star A and Star B have the same orbital distances to their companion stars, but star A's companion shows large Doppler shifts compared to star B's companion. Which star is probably more massive, star A or star B?" or "Star A and star B have the same mass, but star A's companion shows a smaller Doppler shift compared to star B's companion. Which star's companion is probably at a larger orbital distance, star A's companion or star B's companion?"
(69): Be able to answer simple proportionality questions having to do with both the period equation and the equation of orbital velocity, such as: "Suppose the companions star A and star B show the same Doppler shifts, but star A's companion has a period twice as long as star B. Which of the two central stars is more massive? Explain or show your work."
(70): Suppose we are assuming that a binary system is being seen edge-on. We measure the maximum Doppler shift and from that estimate the orbital velocity, then we find the orbital distance using the angular size method (as opposed to using the period equation). We use this information to estimate the mass of the central star. Later, another Astronomer double-checks our data, discovering that while our orbital distance measurement is correct, the system is not eclipsing! The fact that this system is tilted away from being edge-on means that our estimate of the mass is incorrect. Is our estimate higher than the true mass or lower than the true mass? Explain. (TQ #20)
(71): Given the mass-luminosity relation, be able to relate this to the method we use for estimating the lifetimes of stars. Use this method to help explain why more massive stars (despite the fact that they have more "fuel" to burn compared to the Sun) live shorter lifetimes.
(72): A recent important political topic is the issue of sampling in the 2000 U. S. Census. Should the census be an actual enumeration of people, or should statistically undercounted people be included? In 2-3 sentences each, summarize each side of this position. Several good documents on this issue can be found at http://www.louisville.edu/library/ekstrom/govpubs/goodsources/census/csample.html. (TQ #20)
(73): Answer the following questions about "nebulium": What led scientists to think nebulium was a previously unknown element? What is nebulium, and why weren't we able to originally identify it correctly? What are forbidden lines, and why do we not see forbidden lines in typical laboratory spectra while we see them all the time in interstellar gas clouds? (TQ #21)
(74): Related to the nebulium question: What are forbidden lines, and why do we not see forbidden lines in typical laboratory spectra while we see them all the time in interstellar gas clouds? (TQ #22)
(75): Imagine a sample of the 1,000 stars with the highest surface temperature. Would this sample be representative? Explain. Imagine a sample of the 1,000 stars with the highest apparent luminosity as seen from the Earth. Why would this sample not be representative of the stars in our galaxy?
(76): Imagine a sample of the 1,000 nearest stars to Earth. Would this sample be representative? Explain. What is the Copernican Principle, and how does it apply here?
(77): What is the difference between gas and dust? What sort of light does each emit and why?
(78): Explain why the Sun appears red when near the horizon. Also, explain why the sky is blue.
(79): The Interstellar Medium (ISM) has two effects on stars, extinction and reddening. Explain why stars appear redder when seen through a cloud of gas and dust. Explain the effect that extinction has on our estimate of the apparent luminosity and distance to stars.
(80): Suppose we don't take into account the reddening of starlight by the ISM. How will our estimate of the surface temperature of the star differ from the true surface temperature? How will our estimate of the absolute luminosity differ? What about our distance estimate?
(81): Given the modified form of the inverse square law (with the ISM correction term "X" included), explain how we find X. Explain one method we use to determine the type and number of gas atoms along our line of sight.
(82): What is pressure equilibrium? Given the pressure equation, explain why the condition of pressure equilibrium leads to the inverse relationship between density and temperature in the ISM.
(83): What are the three ingredients necessary for life? What is a possible source for each ingredient?
(84): On the 5-km highway of time representing the history of Earth, what length accurately reflects all of recorded human history?
(85): Critics of evolution wonder how a process based on random chance could result in extremely complex organisms. How do biologists respond to this argument?
(86): What discovery did the Magellan spacecraft make about the recent geological history of Venus?
(87): What recent evidence discovered in Antarctica implies that life may have once existed on Mars?
(88): What is the habitable zone? Explain how recent discoveries of life in extreme environments (e.g. black smokers, methane ice, etc.) has affeted our view of a habitable zone. What is a "gravitational" habitable zone?
(89): What is self-gravity? Given the equation for self-gravity, explain why the self-gravity of a typical molecular cloud (typically thousands of times more massive than a star like our Sun) is so small. Explain how a triggering event (such as a nearby supernova explosion) can change an object's self-gravity, initiating star formation. Given two clouds of the same mass but different sizes (or same size but different mass) but able to tell which has stronger self-gravity.
(90): Why are cool, dense interstellar clouds called "molecular clouds"? (Your book has some background on this, too).
(91): Read the following article about organic molecules in interstellar clouds here then answer the following: How do we know that roughly 30 tons of complex organic molecules are "raining" down into our atmosphere? How do we think these molecules originated in molecular clouds, and what does star formation (and ultraviolet light from new stars) have to do with it? What role might these molecules play in an origin of life scenario? What implications does this research have on the possibility that life might exist elsewhere outside our solar system? (TQ #23)
(92): During the collapse of a molecular cloud, name and explain what is happening to the self-gravity, the density, the temperature and the outward-pushing pressure of the cloud.
(93): Why do stars have a minimum mass? In other words, why is it that objects with masses smaller than about 8% of the mass of the Sun never form into stars?
(94): What is hydrostatic equilibrium (HSE)? Explain what happens to a star's outward-pushing pressure, self-gravity, density, size and temperature as it expands and contracts. For example, suppose a star has a very large outward pushing pressure. What changes would occur with these other quantities and how would the star find equilibrium again? What if the star's outward pushing pressure were very small compared to the self-gravity?
(95): During the main sequence lifetime of the star, the temperature of the core slowly increases. Explain why this occurs (two reasons) and how this affects the absolute luminosity of the star and the overall size of the star (via HSE and increased outward pushing pressure)
(96): Read the following brief article about the Faint Sun Paradox, http://earthsky.com/2000/es000226.html and then state the basic paradox and how the Earth has "resolved" this paradox through changes in its atmosphere. (TQ #24)
(97): By the end of the sun's main sequence (Hydrogen-burning) phase, it will have grown to such an enormous size that it will turn red in color instead of its characteristic yellow. Explain why the Sun will change color like this.
(98): In the Sun's core, Helium fusion will begin eventually but only after the density and temperature reach a much higher value than they needed to for Hydrogen fusion. Explain in detail two reasons why Helium fusion requires higher density and higher temperature compared to Hydrogen fusion.
(99): Do some research on the World Wide Web regarding the "Anthropic Principle" and define two versions of it (Weak, Strong, etc) in your own words. Give three examples of an "Anthropic Coincidence", the kind of thing that leads people to propose the Anthropic Principle in the first place. (TQ #25)
(100): Explain how the H-R diagram of a cluster evolves over time. How do these changes confirm our ideas about the relationship between stellar mass and main sequence lifetime?
(101): Explain what a planetary nebula is and why (generally) it occurs. Why is this fate suffered mainly only by low-mass stars (less than about eight solar masses) instead of high mass stars?
(102): What is different about Iron fusion compared to the fusion of other, lighter elements? Why does the onset of iron fusion signal the end of the lifetime of even the most massive stars? What role do supernovae play in the existence of elements heavier than Iron on Earth?
(103): Define metal and metallicity. How and why does the metallicity of the ISM change over time?
(104): We've talked about blue stars, yellow stars and red stars. Why do we not see green stars in the night sky? Do some research on the web to find out. (TQ #26)
(105): Search the web to find out about "blue stragglers". What are they, and why do they evolve differently from ordinary stars? (TQ #27)
(106): Read http://hubblesite.org/newscenter/archive/2000/35/text to find out about the strange object RX J185635-3754. What is this object? How do we know that it originated from a grouping of newly formed stars in the constellation Scorpius? (TQ #28)
(107): Who is Jocelyn Bell? Briefly summarize and explain her famous discovery. (TQ #29)
(108): What does it mean to say that we are communicating already? What do our signals sound like at various distances from the Earth? Explain.
(109): Why do radio wavelengths work as the best way to communicate with potential extraterrestrials? How do we decide where in the spectrum to look for extraterrestrial signals?
(110): What is the Fermi paradox, and what is one possible response?
(111): What is an example of an observation Galileo made to show that objects in the Universe are not static like paintings on the inside of cathedrals?
(112): What arguments can you make that evolution is very unlikely to result in intelligence? What is an emergent property? Explain this concept in general, and then give one example.
(113): How and why does the lifetime of a civilization relate to the probability that we are not alone?
(114): What is a pulsar? How is it related to a neutron star? Why do some neutron stars appear to be pulsars on Earth while most do not?
(115): What is a black hole? How do we use the concept of escape velocity to define the boundary (event horizon) of a black hole?
(116): Use the concept of conservation of angular momentum to explain why some neutron stars spin incredibly fast.
(117): Explain how astronomers use observations of binary star systems to "prove" the existence of black holes.
(118): Explain how the force of gravity of a black hole is similar to and different from a normal object like the Sun. Be able to answer questions like, "The Sun's radius is 400,000 miles. Who would feel stronger gravity? An astronaut at the surface of the Sun or an astronaut 400,000 miles from a one-solar-mass black hole? Explain. What if the distance from the center of both were 100 miles? Explain."
(119): Does the metallicity of a main sequence star change over time? Why or why not? How does the metallicity of an old main sequence star compare to the metallicity of a young main sequence star, and why would you expect them to be different?
(120): Be able to answer (with explanations) questions comparing the metallicity of two stars, such as "Star X is the same size, mass and temperature as the sun, but it is about 3 billion years older. Which has a higher metallicity, X or the sun?", "Star X is a main sequence star with an unknown age that has a mass ten times that of the Sun. Which has a higher metallicity, X or the sun (or can you not tell)?" and "Star X is a main sequence star with an unknown age that has a mass one half that of the Sun. Which has a higher metallicity, X or the sun (or can you not tell)?"
(121): What causes variable stars to pulsate? Why do larger stars tend to have longer pulsation periods?
(122): What are Cepheids? Explain step-by-step how to use the Cepheid Period-Absolute Luminosity, or P-L relation to find the distance to a star cluster or distant galaxy.
(123): How do colors and ages correlate for individual stars? Explain why regions of young stars or regions with lots of star formation (like the disk) tend to have a blue color. Explain why regions with mostly older stars and no recent star formation (like the bulge and halo) tend to appear red.
(124): How do we know that there is a supermassive black hole (20 million times the mass of our Sun) at the center of our galaxy? Will this black hole eventually suck up all the material in our galaxy? Why or why not?
(125): Describe the initial collapse of the Milky Way galaxy from a roughly spherical cloud into a disk of gas and dust. Why did the galaxy collapse into a disk shape instead of into a small point?
(126): Why did the stars that formed during the collapse of the galaxy not become a part of the disk? Explain the two different types of collisions that we discussed in class and how this implies that stars and clusters that form in the halo will remain in the halo.
(127): Given the equation of orbital velocity, be able to explain the basic shape of the Keplerian rotation curve. Why does our solar system follow the Keplerian curve while Astronomers initially anticipated the rotation curve of the Milky Way galaxy would not follow this curve (but instead have orbital velocities slightly higher than the Keplerian prediction)?
(128): Explain how the flat rotation curve of our galaxy leads us to believe that the galaxy has a very large amount of dark matter, much more than the visible matter in stars, gas and dust that we can easily see.
(129): What was Vera Rubin's primary contribution to Astronomy? How did she make her discovery?
(130): How does Tony Tyson search for dark matter in very distant galaxies? What are "faint blue galaxies" and what role do they play in the search for dark matter?
(131): What are the three primary things you look for in a location when you try to place a multimillion dollar observatory? Briefly explain each.
(132): Read the following website about an ongoing experiment to detect WIMPs: http://hepwww.rl.ac.uk/ukdmc/dark_matter/wimp.html. How does the UKDMC (United Kingdom Dark Matter Collaboration) propose to detect WIMPs? Why is the WIMP detector located far underground? Even underground, the detectors cannot escape a major source of noise. Describe it. (TQ #30)
(133): What are MACHO's? Explain gravitational lensing and how it is used to detect MACHO's. Why does a MACHO intervening along the line of sight to star cause the star to brighten rather than dim?
(134): How can Astronomers tell whether a star's variation in brightness is due to a gravitational lensing event rather than some other kind of variation? As part of your answer, explain why lensing variations are different than other variations (e.g. variable stars, binaries, flares).
(135): How do we estimate the amount of MACHO's in our galaxy? What conclusion have Astronomers reached about the fraction of the dark matter that consists of MACHO's?
(136): Read the following article about relativity: http://personal.tcu.edu/~dingram/edu/pine2.html and answer: If you are standing still on the surface of the Earth, are you truly at rest? Give some examples of things contributing to your overall motion in the rest frame of the Universe. Explain the "twin paradox" at what causes it. (TQ #31)
(137): Read the article at http://mplanet.anu.edu.au/planeet.html and answer the following: How do we use very precise observations of microlensed stars to deduce the existence of extrasolar planetary systems? (TQ #32)
(138): The image located at http://imgsrc.hubblesite.org/hu/db/1994/41/images/b/formats/web_print.jpg tells the story of a search with the Hubble Space Telescope search for very low mass stars in a representative sample of nearby stars, the core of a globular cluster. Read http://hubblesite.org/newscenter/archive/1994/41/image/b and explain the evidence that tells us very low mass stars do not account for the dark matter in our galaxy. (TQ #33)
(139): How would we detect solitary black holes if they consitituted a significant fraction of the dark matter? Why does it look like we will be unlikely to test this hypothesis in the near future?
(140): Explain why the Cepheid P-L relation as a method of distance determination is distance limited. In other words, why doesn't it work beyond a certain distance from the Earth?
(141): Describe how we use masers to determine the distances to some nearby galaxies.
(142): Explain why the maser technique is distance-limited. Why will this technique improve in effectiveness over time?
(143): Why is the maser technique so important with respect to other distance determination methods, despite its limitations? On a related note, why do we use multiple techniques to find the distances to the same galaxies?
(144): Explain what the Tully-Fisher (TF) relation is. Describe briefly how one would use the TF relation to find the distance to an edge-on galaxy.
(145): Explain how the inclination angle can affect our distance estimate. For example, suppose we fail to take the inclination angle of a galaxy into account so that the radial velocity we measure for that galaxy's rotation is smaller than the true rotation speed. Will we underestimate or overestimate the distance to that galaxy? Explain.
(146): Explain why the TF relation is distance limited. In other words, why doesn't it work as a distance determination technique beyond a certain distance from the Earth?
(147): Explain why individual stars are not useful as standard candles for very distant galaxies. Explain why galaxies are not very useful as standard candles.
(148): Summarize the difference between a Type Ia and a Type II supernova. There is a great web site for this, if you want to use it to help (but your book also tells the story) at: http://www.pbs.org/wgbh/nova/universe/supernova.html.
(149): Why are Type Ia supernovae such great standard candles? What do you have to do to find these standard candles (can you just look at any galaxy and find an ongoing supernova)?
(150): About every six seconds on average, the Earth is hit by a "fastball" from space. Read http://www.gsfc.nasa.gov/scienceques2002/20021213.htm and answer the following: What are these fastballs (what is another name for them, and what is their composition)? What is one possible theory for their origin? Why do we think the point of origin must be nearby in terms of galactic distances? (Another good source for this question and the next one is at http://www.srl.caltech.edu/personnel/dick/cos_encyc.html.) (TQ #34)
(151): Read a little more about cosmic rays at http://www-spof.gsfc.nasa.gov/Education/wcosray.html and answer: What is the likely origin for the most common (not fastballs) galactic cosmic rays that don't come from the Sun? Why do cosmic rays seem to come evenly from all directions on the sky (this is part of what makes it so difficult to guess their origins)? (TQ #35)
(152): Explain how we can use Hubble's Law to find the distance to a galaxy. Explain the difference between the rotation velocity of a galaxy and the radial velocity of a galaxy.
(153): Explain the merger hypothesis (that describes why ellipticals are different from spirals and how ellipticals form). List the general properties of spirals vs ellipticals and discuss how these are consistent with the merger hypothesis.
(154): Elliptical galaxies tend to be found near the centers of galaxy clusters while spirals are typically found near the edges of clusters or outside of galaxy clusters. Explain how/why this fact is consistent with the merger hypothesis.
(155): Read the article at http://imagine.gsfc.nasa.gov/docs/features/exhibit/cgro_blazars.html and (with the help of your book's chapter 27, if needed), explain what a blazar is. Do quasars and blazars originate from the same type of object? If so, explain why they appear differently. If they don't, explain where blazars come from. (TQ #36)
(156): Find out about Gamma-Ray Bursters (GRB's), and answer the following questions: Explain how we know that GRB's are not nearby, within our own galaxy. Describe one possible model that explains the incredible energy generation needed to power GRB's. (TQ #37)
(157): How is the cosmic background radiation (CBR) related to the big bang?
(158): Who predicted the existence of the CBR? Who first discovered/observed the CBR?
(159): Why must we observe the CBR from above the Earth's atmosphere?
(160): Why are major experiments like the rocket-borne experiment typically performed largely by graduate students rather than professional engineers and scientists?
(161): How do Astronomers hope to use the CBR to study the early "dark age" of the Universe before galaxies formed? In other words, what puzzle about the early Universe do we hope to solve by observing the CBR?
(162): What did John Huchra and Margaret Geller learn about galaxies, and how does this relate to the puzzle that Andrew Lang, Paul Richards and their colleagues are trying to solve?
(163): What did the COBE experiment learn about the CBR, and how did this finding compare with Toshio Matsumoto's and Andrew Lang's previous rocket-borne experiment to measure the CBR?
(164): Explain how we know that quasars (QSO's) are hundreds of times more luminous than a typical galaxy, trillions of times more luminous than a typical star.
(165): How do we know that QSO light does not come from typical stars or galaxies?
(166): How do we know that QSO's have small sizes compared to galaxies? Explain fully (don't just say "because of their timescale of variability" or something ... explain that whole concept).
(167): Describe how lookback time is related to distance. How do we know that quasars only existed in large numbers back when the Universe was about 2-4 billion years old?
(168): Why do we think QSO's are powered by massive black holes? How do we think QSO's are related to galaxies? Explain why we make this link.
(169): If you were to draw a graph of galaxy metallicity vs distance from Earth, taking lookback time into account, how would it look? Would galaxy metallicity seem to increase at greater distances? Decrease? Or remain the same? Explain. (TQ #38)
(170): How would you expect the abundance of Hydrogen relative to other elements to look if you plotted it for galaxies at various distances from Earth, as in question 169? Would the abundance of Hydrogen increase with increasing redshift? Decrease? Stay the same? Explain. (TQ #39)
(171): Be able to plot a graph of a car race at various times as we did in lecture given some basic data. Given a graph of a car race, be able to find the slope of the graph and the age of the race.
(172): What is the Hubble constant? A Hubble constant of 70 implies that the age of the Universe is 10 billion years. What if the Hubble constant were recalculated to be 50...how would our estimate of the age of the Universe change (younger or older)? Explain.
(173): What is the Copernican Principle? Explain why the Hubble relation, which indicates that all galaxies seem to be moving away from our location, is not a violation of Copernican Principle.
(174): Explain how and why Astronomers hoped to use Hubble's Law as an independent method for estimating the density of the Universe. How would a high vs a low density (and a zero density) Universe compare? Explain.
(175): Explain how current observations of galaxy radial velocities and distances compare to the expectations of Hubble's Law under the influence of gravity. Explain why these observations lead us to believe that the Universe is accelerating away from us in all directions.
(176): This will require some research in your book or on the web. Explain what the Cosmological Constant is. Why did Einstein originally introduce the idea of a Cosmological Constant? Why was it later abandoned? Why do some astronomers claim that the evidence from question 175 leads us to believe that there may be indeed be some form of cosmological constant? (TQ #40)
(177): Explain Olbers' paradox. Explain why a Universe that is either finite in space or time (or both) saves us from having a bright night sky.
(178): What is the visible horizon? Why can't we see anything outside of our visible horizon?
(179): How are the ages of stars determined in our galaxy? How do the maximum ages found compare with our estimates for the age of the Universe? Explain the significance of this in terms of the Big Bang.
(180): Although most Astronomers are confident that the Big Bang theory is likely the correct model to explain the observational facts we studied, this theory still has some minor but important inconsistencies. Why are Astronomers so confident of the Big Bang theory and skeptical about inconsistencies in the Big Bang?
(181): Based on the discussions in your book sections 29-1 and 29-2, explain the horizon problem and how the theory of inflation resolves the problem. (We didn't talk about 181 or 182 in class today, but it will really help you for tomorrow's discussion if you read about these in your book first).
(182): Based on the discussions in your book sections 29-1 and 29-2, explain the flatness problem and how the theory of inflation resolves the problem.
(183): What is the Cosmic Background Radiation (CBR)? Where does it come from? Why does it originate just inside our visible horizon?
(184): Explain why the current structure of the Universe led Astronomers to believe that the CBR must have a lumpy nature, with measurable fluctuations.
(185): Explain how the existence of the CBR, the shape of its spectrum and its fluctuations are seen as convincing evidence of the Big Bang theory. What is different about this evidence in favor of the Big Bang compared to Hubble's original observations? Why are the observations of the CBR really seen as the key to confirming the Big Bang instead of just relying on Hubble's Law?
(186): Explain why effectively no fusion occured prior to a time when the Universe was about 1 second old. Explain why nucleosynthesis ended when the Universe was about 3 minutes old.
(187): Explain why the density of matter in the Universe has a bearing on how much Helium was created during nucleosynthesis in the first three minutes of the Universe's existence. If the Universe had been more dense at the time, would more Helium have been created? Less? The same amount? Explain.
(188): How do we know whether or not the Universe will expand forever or at some point turn around and collapse? How do we try to answer this question? What is the critical density? Why is the study of dark matter important in this question of the fate of the Universe?