Physics 20083 - Complete Study Guide

Here is some advice and responses to frequently asked questions about study guide emails.

(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, what two things happen to its spectral curve? 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. Be able to sketch a graph of a warmer or cooler object given a spectral graph of an object with a certain temperature.

(3)
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.

(4)
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)

(5)
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)

(6)
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)

(7)
Three of the most easily recognizable constellations that are up in the sky at this time of year are Orion, Canis Major, and Leo. Find the following information about these three constellations:

This is pretty easy to find on the web. A good place to go for mythology is http://www.emufarm.org/~cmbell/myth/myth.html, but remember to keep your summary fairly short so it is easy to remember the most important parts. A good place to go for simple star charts is http://www.fcps.k12.va.us/DIS/OHSICS/planet/constell/constell.htm. To find the approximate altitude and azimuth (azimuth means direction along the horizon, like northeast, south, west, etc), consult the Starry Night software that comes with your book (this is also installed on the computers in the Astronomy lab, which you can use if you finish early in lab) ***OR*** go outside and *FIND* them with your own two eyes on a clear night (all are easily visible this time of year). There are some web sites that will provide you with interactive sky charts, but different computers will work with different sites, so it is up to you to go looking. http://directory.google.com/Top/Science/Astronomy/Amateur/Sky_Maps_and_Atlases/ is a good place to start. When you are done, go out at night and find the constellation and explain what you know to a friend or classmate. It's fun to do and easier to remember that way. (TQ #4)

(8)
Explain why the Sun appears red when near the horizon. Also, explain why the sky is blue.

(9)
Describe 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.

(10)
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.

(11)
Explain how we use the principles of atomic emission and absorption to deduce the composition of different elements in clouds of gas, stars, etc.

(12)
Explain how Ernest Rutherford discovered the nature of the atom (that it is a dense nucleus surrounded by a diffuse cloud of relatively light weight electrons). (TQ #5)

(13)
What are Fraunhofer lines? (TQ #6)

(14)
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?"

(15)
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.

(16)
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)

(17)
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)

(18)
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 diameter of the telescope affects each one.

(19)
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?

(20)
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.

(21)
Explain qualitatively how interferometry works to improve the resolution of radio telescopes.

(22)
What causes stellar images to appear blurred ("seeing") when we look at them through ground-based telescopes? Why don't planets twinkle like stars do?

(23)
Briefly explain how adaptive optics works to correct for atmospheric seeing.

(24)
Answer the following questions based on your reading of Philosophy and the Scientific Method: The credibility of a scientific idea isn't really related to its "weirdness" or how it relates to common sense but instead to its "epistemological status". Name and explain the primary distinction between scientific theories and ideas proposed by Bill Maupin or Oral Roberts. (TQ #9)

(25)
More on the Pine reading: What is an example of a positive benefit of an irrefutable idea like Maupin's? What is the primary drawback to a system of knowledge based on multiple irrefutable beliefs? (TQ #10)

(26)
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?")

(27)
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?

(28)
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 #11)

(29)
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? How does a PET scanner locate cancerous tissue? Why does the cancerous tissue look different from normal tissue to a PET scanner? An alternate site is at http://www.triumf.ca/welcome/petscan.html and http://www.kccancercenters.com/PET.html. (TQ #12)

(30)
Read the Frequently Asked Questions (FAQ) about fusion energy at http://fusedweb.pppl.gov/FAQ/section1-physics.txt and answer the following: Why doesn't fusion happen under normal conditions? In other words, why does it only happen in the cores of stars? What are Deuterium and Tritium? Why is it easier to fuse Deutrerium and Tritium as opposed to normal Hydrogen? Two different kinds of fusion reactions we've tried on Earth are inertial and magnetically confined. Describe how each works. (TQ #13)

(31)
Explain why both high temperature and high density are needed in order for fusion reactions to take place

(32)
How is the core of the Sun defined? What is the envelope of the Sun?

(33)
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

(34)
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 #14)

(35)
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?

(36)
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?

(37)
Your book can help you answer some questions about sunspots. For example, the typical temperature in the center of a sunspot is about 4300 K. Why, then, do these spots in the Sun's photosphere appear dark to us? Describe the rotation of the Sun (does it rotate uniformly or do different parts rotate at different speeds) and how we used sunspots to observe this phenomenon. (TQ #15)

(38)
More on sunspots: Explain how we know that sunspots are associated with locally strong magnetic fields on the sun's surface. Describe the sunspot cycle. How do the locations of sunspots on the Sun typically change over the course of a sunspot cycle (are they uniformly distributed over the Sun, closer to the poles, closer to the equator, does this change over time, etc)? (TQ #16)

(39)
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, using figure 5-14 from the text as a guide.

(40)
Define ionization species. Why are ionization species related to temperature? 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?

(41)
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?

(42)
What is coronium? What elements is it really made of? Read http://science.nasa.gov/ssl/pad/solar/corona.htm to find the answer. (TQ #17)

(43)
Use a conservation of energy argument to help explain why coronal gas temperatures are thousands of times higher than the temperature of the Sun's photosphere.

(44)
Explain how to use parallax to determine the distance to a nearby star. Given the parallax equation, be able to answer proportionality 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?"

(45)
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.

(46)
Read about the GAIA mission at http://sci.esa.int/gaia and answer the following (use the sidebar menu and link to "Objectives", etc.): What is the overall purpose of the proposed GAIA mission. Name and briefly explain three major areas of Astronomical research to which GAIA will contribute. (TQ #18)

(47)
What does the "N" stand for in the Drake equation? What are two examples of factors that must be multiplied together in the Drake equation?

(48)
The first extrasolar planetary systems discovered were similar to the 51 Pegasi system. Briefly explain two reasons these systems are unlikely to have a planet like Earth with life present.

(49)
What are three basic ingredients that life needs in order to get started on a planet?

(50)
Summarize Peter Ward's argument that Earth-like life is probably extremely rare in the Universe.

(51)
Though different kinds of intelligence and sophistication are present in many species, Ward thinks technological development (and thus the construction of radio telescopes) will be extremely rare. Explain his reasoning.

(52)
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. For example, describe how you could determine the distance to a star thousands of parsecs away (too far for parallax), assuming that star has spectral characteristics identical to our Sun.

(53)
Any star within range of our ability to measure parallax can be used as a "standard candle" for the method described in 52. How do we determine the absolute luminosities of these standard stars?

(54)
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 #19)

(55)
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. What was her discovery, and how did she make this discovery? (Your book can help, and lots more information can be found on the web with a simple search). (TQ #20) (this is the last thought question for part 1 of the course).

(56)
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?

(57)
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.

(58)
Given the period equation and the equation of orbital velocity, explain how we can find the mass of the Sun. For example, we know the Earth's orbital distance (93 million miles) and the period (365 days). How could we use that information to find the Sun's mass?

(59)
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.

(60)
Would the spectral lines split and merge in a face-on system (where the orbital plane is perpendicular to your line of sight)? Explain.

(61)
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.

(62)
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.

(63)
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.

(64)
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.

(65)
What is the difference between the terms "larger" and "more massive"? Are larger stars necessarily more massive? Explain.

(66)
Explain two reasons why spectral line widths should depend on the density of a gas (and therefore the size of a star).

(67)
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?

(68)
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. Answer questions like, "If star A and B have the same temperature and mass, but star B has broader lines, which star is larger?" or "If star A is cooler than star B , but the two stars have identical spectral line widths and identical masses, what can you say about the relative sizes of the two stars?" Explain your answers in each case.

(69)
Explain how we use spectroscopic parallax to find the distance to a star. 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."

(70)
Given the equation of angular size, briefly explain how you could find the linear size (R) of an object given its angular size and the distance from Earth. Why can we only measure the linear size of a few stars directly this way?

(71)
Three of the most easily recognizable constellations that are up in the sky at this time of year are Ursa Major, Cepheus and Auriga. Find the following information about these three constellations:

This is pretty easy to find on the web. A good place to go for mythology is http://www.emufarm.org/~cmbell/myth/myth.html, but remember to keep your summary fairly short so it is easy to remember the most important parts. A good place to go for simple star charts is http://www.fcps.k12.va.us/DIS/OHSICS/planet/constell/constell.htm. To find the approximate altitude and azimuth (azimuth means direction along the horizon, like northeast, south, west, etc), consult the Starry Night software that comes with your book (this is also installed on the computers in the Astronomy lab, which you can use if you finish early in lab) ***OR*** go outside and *FIND* them with your own two eyes on a clear night (all are easily visible this time of year). There are some web sites that will provide you with interactive sky charts, but different computers will work with different sites, so it is up to you to go looking. http://directory.google.com/Top/Science/Astronomy/Amateur/Sky_Maps_and_Atlases/ is a good place to start. When you are done, go out at night and find the constellation and explain what you know to a friend or classmate. It's fun to do and easier to remember that way. (TQ #21)

(72)
What is the name of the brightest star in the nighttime sky (in terms of apparent luminosity)? How does its absolute luminosity and mass compare to our Sun? It turns out that this star is part of a binary system. Describe this bright star's companion. What is the name of the closest star (it is also a binary system) in the nighttime sky (not counting the Sun, obviously)? Though there are many places to look for this information, a fun web site to explore that has the answers to these questions is The Astronomy Picture of the Day. (TQ #22)

(73)
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? Imagine a sample of the 1,000 stars with the highest surface temperature. Would this sample be representative? Explain.

(74)
Imagine a sample of the 1,000 nearest stars to Earth. Would this sample be representative? Explain. As part of your answer, briefly explain the basis of the Copernican Principle.

(75)
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.

(76)
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?

(77)
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 (21-cm radiation is a forbidden line, by the way), and why do we not see forbidden lines in typical laboratory spectra while we see them all the time in interstellar gas clouds? (TQ #23)

(78)
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)? 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 #24)

(79)
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 #25)

(80)
From the Electronic Course Reserves, read the Scientific American (Jan 2004) article Our Growing, Breathing Galaxy and answer the following: What are HVC's? What is their composition and where are they located? How does the "galactic fountain" model explain the existence of HVC's? What is the origin of the Magellanic Stream? How could the Magellanic Stream help explain the existence of HVC's? (TQ #26)

(81)
More on the previous article: Explain why we now know HVC's do not originate from the Magellanic Stream or the "galactic fountain". How do we know that IVC's (Intermediate Velocity Clouds) *do* originate from the "fountain" model (two pieces of evidence)? So, finally, what is believed to be the true source of the HVC's? (TQ #27)

(82)
Given the modified form of the inverse square law (with the ISM correction term "X" included), explain how we find X using interstellar absorption lines. How and why do interstellar lines differ from other absorption lines in stellar spectra?

(83)
Why are cool, dense interstellar clouds called "molecular clouds"? (Your book has some background on this, too).

(84)
What is 21-cm radiation? From what kind of atom does it originate? Why is it so important to our study of the ISM?

(85)
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.

(86)
During the collapse of a molecular cloud, what is happening to the self-gravity, the density, the temperature and the outward-pushing pressure of the cloud? Briefly explain why the temperature increases.

(87)
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?

(88)
Read the article, "The Discovery of Brown Dwarfs" from the Electronic Course Reserves (Scientific American, April 2000, PDF version also available here) and answer the following: What is a brown dwarf? What is the "brown dwarf desert"? How and why do the spectral lines of brown dwarfs differ from other stars (which element's fingerprint is usually present in brown dwarfs and why is this not present in normal stars)? It turns out the reason we had trouble finding brown dwarfs initially is that we were looking in the wrong place. Where were we looking for brown dwarfs, and why are they not typically found in those kinds of systems? (TQ #28)

(89)
Search the web for information about the "Faint Sun Paradox". Explain what the paradox is and how it has been "resolved" by changes in the Earth's atmosphere over time. (TQ #29)

(90)
During the main sequence lifetime of the star, the size of the star slowly increases. Explain why this occurs. Use the concept of Hydrostatic Equilibrium (HSE) as part of your answer.

(91)
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.

(92)
What is a planetary nebula? Why are they called planetary nebulae when they have nothing to do with planets? Why do some stars undergo this process after the end of the main sequence while other stars avoid it? What causes the nebula?

(93)
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. Name and briefly explain three examples of an "Anthropic Coincidence", the kind of thing that leads people to propose the Anthropic Principle in the first place. As an example, don't just say "The lifetime of Beryllium in a star's core is a hundred millionth of a second." Explain why a deviation from that value would be critical and potentially devastating to the potential for life, etc. (TQ #30)

(94)
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 #31)

(95)
Why do giant stars turn red during the latter part of their lives, even though their cores are burning much hotter?

(96)
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 causes the supernova explosion after iron fusion begins in a massive star's core?

(97)
What role do supernovae play in the existence of elements heavier than Iron on Earth? How do we know that all the heavy elements (heavier than iron) originated in supernova explosions? What role do supernovae play in the formation of planetary systems?

(98)
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 #32)

(99)
Who is Jocelyn Bell? Briefly summarize and explain her famous discovery. (TQ #33)

(100)
Read http://solomon.as.utexas.edu/~duncan/magnetar.html (skip over the sections "for advanced readers" if you like ... none of the questions I ask have answers found in those sections) to learn about magnetars and then answer the following: What is a magnetar? What is a SGR, and how did it get this name? What was the source of the famous (to Astronomers, anyway) "March 5th" event of 1979. How was the location of this source pinpointed? (these questions are all answered in the first four numbered sections). (TQ #34)

(101)
In the August 27 section of the same "Magnetar" web page, there is an interesting story about how a new SGR was detected. Explain how and why the Earth's ionosphere changes in response to a gamma-ray burst (this is one way Astronomers detected the outburst, by monitoring changes in the Earth's ionosphere). Also, explain why AM radio signals carry further at night than they do in the daytime. If you are interested in more detail on this event, you can read about it further here. (TQ #35)

(102)
How does mass transfer occur between stars in a binary system? How can a binary system evolve to the point where one star is a white dwarf and the other is a red giant? Why don't they both evolve in the same way simultaneously?

(103)
Describe how nova explosions occur in binary systems. Explain why recurrent nova systems may be candidates to explode as supernovae in the future. Describe how a Type Ia supernova occurs.

(104)
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? Your book can help you with this one.

(105)
Use the concept of conservation of angular momentum to explain why some neutron stars spin incredibly fast.

(106)
What is a black hole? How do we use the concept of escape velocity to define the boundary (event horizon) of a black hole?

(107)
Search the web to find out about "blue stragglers". What are they, and why do they evolve differently from ordinary stars? (TQ #36)

(108)
Explain how astronomers use observations of binary star systems to "prove" the existence of black holes.

(109)
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."

(110)
What are tidal forces? Explain how tidal forces can result in accretion disks of material around black holes. Why can black holes exert much stronger tidal forces on some objects compared to, say, stars?

(111)
Read the article about the galactic center at http://science.nasa.gov/headlines/y2002/21feb_mwbh.htm and answer the following: What wavelengths of emitted light are characteristic of material falling into black holes? The material surrounding the black hole in the center of our galaxy seems to be giving off too little energy ... what explanation has been proposed by Astronomers for this observation? Also, what causes the light from the center to flicker occasionally? Another good source is http://antwrp.gsfc.nasa.gov/apod/ap010910.html for the last question. (TQ #37)

(112)
How do colors and ages correlate for individual stars? Do stars change colors during their main sequence lifetimes? In other words, are all young stars blue? Are all old stars red? Explain.

(113)
Define metal and metallicity. How and why does the metallicity of the ISM change over time?

(114)
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?

(115)
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)?"

(116)
Explain how the H-R diagram of a cluster evolves over time. How can we use these diagrams to estimate the ages of clusters?

(117)
Describe the three main parts of the Milky Way galaxy. Why does most of the star formation in the galaxy occur in the disk?

(118)
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?

(119)
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 tend to appear red.

(120)
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?

(121)
When the halo formed during the initial collapse of the galaxy, there were star clusters and gas clouds. Explain why the gas clouds eventually became part of the disk while clusters remained in the halo.

(122)
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)?

(123)
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.

(124)
Three of the most easily recognizable constellations that are up in the sky at this time of year are Hercules, Canis Minor and Corona Borealis. Find the following information about these three constellations:

This is pretty easy to find on the web. A good place to go for mythology is http://www.emufarm.org/~cmbell/myth/myth.html, but remember to keep your summary fairly short so it is easy to remember the most important parts. A good place to go for simple star charts is http://www.fcps.k12.va.us/DIS/OHSICS/planet/constell/constell.htm. To find the approximate altitude and azimuth (azimuth means direction along the horizon, like northeast, south, west, etc), consult the Starry Night software that comes with your book (this is also installed on the computers in the Astronomy lab, which you can use if you finish early in lab) ***OR*** go outside and *FIND* them with your own two eyes on a clear night (this will be difficult for Virgo and Corona Borealis unless you are outside of the city). There are some web sites that will provide you with interactive sky charts, but different computers will work with different sites, so it is up to you to go looking. http://directory.google.com/Top/Science/Astronomy/Amateur/Sky_Maps_and_Atlases/ is a good place to start. When you are done, go out at night and find the constellation and explain what you know to a friend or classmate. It's fun to do and easier to remember that way. (TQ #38)

(125)
Read the following website about an ongoing experiment to detect WIMPs: http://hepwww.rl.ac.uk/ukdmc/dark_matter/wimp.html. What are WIMPs? 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 #39)

By the way, if you are interested in reading more about how we observe neutrinos and estimate their mass, etc., you can read "Detecting Massive Neutrinos" (Scientific American, May 2003) in the electronic course archives, but this is not a required reading.

(126)
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?

(127)
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).

(128)
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?

(129)
Read the article at http://www.mso.anu.edu.au/~psackett/NVWS/index.html, ignore all the math, and answer the following: In what direction should we look for the best chance of observing microlensing? Why? How do we use very precise observations of microlensed stars to deduce the existence of extrasolar planetary systems? (TQ #40)

(130)
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 a significant portion of the dark matter in our galaxy. (TQ #41)

(131)
Name and briefly explain two methods by which we can detect solitary black holes if they consititute a significant fraction of the dark matter. Why does it look like we will be unlikely to look for black holes via lensing in the near future?

(132)
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.

(133)
Be able to answer questions about Cepheid distance determination, such as: "Cepheid A has a period twice as long as Cepheid B. Which Cepheid is more luminous? If both stars have the same apparent luminosity, which is further away?" (TQ #42)

(134)
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?

(135)
Describe how we use masers to determine the distances to some nearby galaxies. Why is the maser technique limited to only the most nearby galaxies?

(136)
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?

(137)
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.

(138)
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 absolute luminosity of that galaxy? What about our estimate of the distance? Explain. (see #133 for a question with similar logic).

(139)
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?

(140)
Explain how the standard ruler method of distance determination works. Why is this method unreliable? Explain how we can use statistical arguments (e.g. using the largest/brightest galaxy in a cluster as a standard instead of a randomly selected galaxy) to improve the technique.

(141)
Briefly summarize how the standard candle method of distance determination works. Explain why individual stars are not useful as standard candles for very distant galaxies. Explain why galaxies are not very useful as standard candles. Explain how we can use statistical arguments (e.g. using the brightest galaxy in a cluster as the standard) to improve the technique.

(142)
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.

(143)
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)? Why are they so difficult to find?

(144)
Explain the role that parallax and the Cepheid distance determination technique played in figuring out the absolute luminosities of Type Ia supernovae. Why was the Hubble Space Telescope an important tool in this process?

(145)
Use your book and/or the web to find out about the Eddington Limit, which results in a maximum mass for stars of somewhere between 100-300 solar masses. Explain what the limit is and why stars have a maximum mass. (TQ #43)

(146)
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.

(147)
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.

(148)
Describe two other pieces of evidence we've found that indicate 90% of the matter in the Universe is not visible: specifically, gravitational lensing by galaxy clusters and motions of galaxies within cluster. For each, explain how we estimate the mass of the galaxy cluster.

(149)
Explain how we know that quasars (QSO's) are much more distant than nearby galaxies. How do we know they are hundreds of times more luminous than a typical galaxy, trillions of times more luminous than a typical star?

(150)
How do we know that QSO light does not come from typical stars or galaxies?

(151)
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).

(152)
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 #44)

(153)
Find out about Gamma-Ray Bursters (GRB's), and answer the following questions: Explain how (without using redshifts, as with quasars) 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 #45)

(154)
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. Also, QSO's are only found very far away from us and not nearby. Explain why this isn't a violation of the Copernican Principle.

(155)
Describe how lookback time is related to distance. How do we know that quasars only existed in large numbers back when the Universe was only a few billion years old?

(156)
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 #46)

(157)
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 156? Would the abundance of Hydrogen increase with increasing redshift? Decrease? Stay the same? Explain. (TQ #47)

(158)
If we were to draw a graph of the ratio of spirals to ellipticals in clusters vs distance from Earth, how would it look? Would the ratio seem to increase at greater distances? Decrease? Explain. (TQ #48)

(159)
Read the article "The First Stars in the Universe" (Scientific American Special Edition, September 2004) and answer the following questions: What are "Population III" stars? How and why are these stars linked to the appearance of quasars? Why was it harder for stars to form during the first billion years or so as opposed to now (another way of asking this is: why was the Jeans mass larger long ago)? Why was the second generation of star formation more efficient (what did metals have to do with it)? Early in the history of the Universe, most of the gas became ionized. What caused this? (TQ #49)

(160)
Read the article "Rip Van Twinkle" (Scientific American, May 2001) and answer the following questions: What is the "age crisis" in terms of cosmology, and how was it resolved? What evidence indicates that globular clusters are probably the oldest parts of our galaxy? Explain briefly how and why the metallicity of a star affects how quickly it burns its nuclear fuel. Explain how the Hipparcos satellite resulted in younger age estimates for globular clusters. (TQ #50)

(161)
Explain why scientists were looking for gamma-rays in the first place, why the first gamma-ray detecting satellites were sent into space.

(162)
Describe how Astronomers thought nearby neutron stars might be capable of producing gamma-ray bursts.

(163)
Describe the first evidence that convinced Astronomers gamma ray bursts do not originate from within our own Milky Way galaxy. Note that 162 and 163 are also asked as TQ #45 (study guide question 153).

(164)
What was the goal of the gamma-ray observations that were to be made by the High Energy Transient Explorer (HETE) and later by Beppo-Sax? Why was it important to view bursts very quickly after detection? What did we hope to learn by doing this?

(165)
What is a hypernova? How does it generate the incredible energy needed to power gamma-ray bursts, according to theorists Stan Woosley and Andrew McFadyen?

(166)
Dr. Arnon Dar thinks gamma-ray bursts may have a connection with why the Search for Extra-Terrestrial Intelligence hasn't been successful so far. Explain.

(167)
Explain what conclusion we can reach about the finite nature of the Universe simply by observing that the night sky is dark.

You can find out more about the various things that contribute to the "background" brightness of the entire night sky by reading "The Cosmic Reality Check" (Scientific American, March 2002), but this is not required.

(168)
How does the expansion of the Universe (Hubble's Law) contribute to the darkness of the night sky?

(169)
How do the maximum ages for stars, clusters and galaxies compare with our estimate of the age of the Universe? Explain the signifigance of this observation in terms of cosmology and the finite nature of the Universe.

These articles are also not required reading, but if you would like a more in-depth discussion of the basic observations of cosmology and the conclusions we reach, well beyond the book's treatment and the lectures, I highly recommend the following articles from Scientific American:

"Four Keys to Cosmology" (Feb 2004) - An excellent introduction and overview of current issues in cosmological research

"The Cosmic Symphony" (Feb 2004) - Summary of current research into the cosmic background radiation and what conclusions we can reach about the Universe from very detailed observations of the background with new satellites like WMAP.

"Reading the Blueprints of Creation" (Feb 2004) - What the large scale structure of the Universe (clusters and superclusters) can tell us about conditions in the early Universe.

"From Slowdown to Speedup" (Feb 2004) - The latest on detailed distance measurements which, thanks to Hubble's Law, seem to imply that the expansion of the Universe is actually accelerating. What does this accleration mean to the future of the Universe?

"Out of the Darkness" (Feb 2004) - The latest conclusions about dark matter and also new information about dark energy, which may be the source of the pressure pushing galaxies apart at an accelerating rate.

"The Myth of the Beginning of Time" (May 2004) - The latest theories about the origin of the Universe. Astronomers try to solve the problem of getting from a singularity (a very, very small, dense glob of material) to the expanding cosmos we see today. String theory is involved, be warned.

(170)
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.

(171)
What is the Hubble constant? A Hubble constant of 70 implies that the age of the Universe is about 14-15 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.

(172)
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.

(173)
Why is it that some galaxies do not appear to be moving away from us? Does that mean Hubble's Law is not valid? Why not?

(174)
If the expansion of spacetime is causing the Universe to expand, is the galaxy itself expanding? Is the solar system expanding? The Earth? Explain.

(175)
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 on a Hubble law graph? Explain.

(176)
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.

(177)
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 176 leads us to believe that there may be indeed be some form of cosmological constant?

(178)
If the Universe were not expanding, what would a Hubble graph look like? Draw it or describe it in detail. (TQ #51)

(179)
What is the Cosmic Background Radiation (CBR)? Where does it come from? Why does it originate just inside our visible horizon? What does it prove about the nature of the Universe long ago? Explain.

(180)
Based on your reading in chapter 29, explain the horizon problem and how the theory of inflation resolves the problem. (TQ #52)

(181)
Based on your reading in chapter 29, explain the flatness problem and how the theory of inflation resolves the problem. (TQ #53)

(182)
Explain why the current structure of the Universe led Astronomers to believe that the CBR must have a lumpy nature, with measurable fluctuations.

(183)
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?

(184)
Explain why the CBR looks redder (cooler) in one direction and warmer (bluer) in the opposite direction, not taking into consideration the much smaller fluctuations discussed in 182.

(185)
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.

(186)
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.