PHYS 20083 - Spring 2006 Complete Study Guide

Physics 20083 - Complete Study Guide

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

(1)

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:

Approximate location in the sky at 10pm tonight (rough altitude and azimuth),
star chart (sketch of the pattern of the 6-8 brightest stars that make up the constellation),
name of one of the bright stars,
2-3 sentence summary of the mythology behind the constellation.

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. There is also Stardome, which works if you set the location to Austin, TX and input the correct local time. 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)

(2)

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)

(3)

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)

(4)

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).

(5)

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.

(6)

How do we use the information from question 5 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)

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"?

(8)

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

(9)

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)

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)

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?"

(12)

Prior to the 20th century, most scientists accepted the idea that the atom was a "plum pudding" of positive charge, seeded with electrons. Ernest Rutherford's famous gold foil experiment changed our view, however. We now know that the positive charge in an atom is confined to a very, very small space in the nucleus, while the electrons "orbit" the nucleus, making the entire atom mostly empty space.

Read the first couple of paragraphs of his original 1911 paper or read the Wikipedia entry on this historic experiment. Explain how Rutherford reached his conclusion by answering the following questions. If the plum pudding model were correct, what would Rutherford have seen? What did he actually observe and how did that lead to his conclusions? (TQ)

(13)

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.

(14)

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)

(15)

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.

(16)

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?

(17)

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.

(18)

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? (Try typing that last question into Google for help.) (TQ)

(19)

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

(20)

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)

(21)

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)

(22)

Explain qualitatively how interferometry works to improve the resolution of radio telescopes. Why is it harder to accomplish with optical telescopes?

(23)

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?")

(24)

Why is chemical energy not accepted as a viable method for energy generation in the Sun?

(25)

A good background reading on Lord Kelvin's thoughts on the age of the Sun is his paper entitled "On the Age of the Sun's Heat". You may wish to read through this to help answer the following, but we also covered this in lecture:

Explain how Kelvin argued that meteoritic impacts are likely not responsible for the Sun's heat. Why is shrinking also not likely to be responsible for the Sun's heat? It is important to understand here that while 30 millions years or so was our best estimate of the Sun's age at the time, Kelvin himself (in the last sentence of his paper) recognized that there was more we did not know, so this estimate was very uncertain, unlike modern estimates related to the theory of nuclear fusion.

(26)

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

(27)

How is the core of the Sun defined? What is the envelope of the Sun?

(28)

Explain how fusion reactions work and how they generate energy.

(29)

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.

(30)

What were two possible solutions to the solar neutrino problem that we discussed in class? One has to do with random oscillations and the other has to do with the reaction rates in the sun's core. Your book is a good place to look for background here as well as the web site http://www.maths.qmw.ac.uk/~lms/research/neutrino.html.

(31)

How to find the article referenced below online:

(1) Go to www.lib.tcu.edu.

(2) In the "Online Catalog Search" box, change the selector from "Words Anywhere" to "Journal/Serial Name Begins With..."

(3) Type "Sciencitic American" (without quotes) into the search box and press the "Search" button.

(4) On the search results page, click on the top listing, which reads "*SCIENTIFIC AMERICAN*"

(5) On records page, click on the first "Full text available" link that you see under detail record 1.

(6) Now you are on the database page for Scientific American Online. In the Find box, type "neutrino" and hit "Search".

(7) The article we're interesting in is the first listing. You may view the text only by clicking on the article title or the PDF version by clicking on that. You will need to read this article to answer the questions below.

Arthur McDonald and his collaborators are among the pioneers in neutrino research. They are largely responsible for the construction and research results of the Sudbury Neutrino Observatory, the device that "solved" the solar neutrino problem in the 1990's by successfully detecting all three different types of neutrions for the first time and confirming that the Sun's core meets with the predictions of the theory of nuclear fusion. Read their article "Solving the Solar Neutrino Problem" in the March 2005 issue of Scientific American and answer the following:

Describe two major sources of noise that must be accounted for in order to accurately count the number of solar neutrinos interacting with the detector. Explain whether the results of the SNO validated the theory of nuclear fusion or refuted it. Why might the number of neutrino counts differ from day to night? What are we hoping to learn from future observations (these last two questions are closely related)?

(32)

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?

(33)

What is the photosphere of the Sun? Explain the concept of limb darkening. Why does it happen?

(34)

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? (TQ)

(35)

More on sunspots: Explain how we know that sunspots are associated with locally strong magnetic fields on the sun's surface. What is the "sunspot cycle"? (TQ)

(36)

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.

(37)

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?

(38)

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?

(39)

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?"

(40)

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.

(41)

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.

(42)

Any star within range of our ability to measure parallax can be used as a "standard candle" for the method described in 41. How do we determine the absolute luminosities of these standard stars?

(43)

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?

(44)

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.

(45)

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

(46)

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

(47)

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.

(48)

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 can help you answer this. (TQ)

(49)

The original stellar classification system was developed and later revised by Annie Cannon. One of her colleagues, Cecilia Payne-Gaposhkin, made an important discovery about stars. Describe the nature of her discovery (which, at the time, was not taken seriously even by her academic advisor). (TQ)

(50)

Explain how atoms like Hydrogen tend to have weaker absorption line strengths at very low temperatures and very high temperatures.

(51)

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.

(52)

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

(53)

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

(54)

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?

(55)

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.

(56)

If a star has a higher temperature, must it always have a broader spectral line? Explain. If a star has a broad line, how would you determine whether the line width is due to temperature or density?

(57)

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?

(58)

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

(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)

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? How does our estimate of the central star's mass compare to the true central star mass in the system? Explain your answer.

(61)

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.

(62)

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.

(63)

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

(64)

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.

(65)

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)

(66)

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?

(67)

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

(68)

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)

(69)

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)

(70)

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

Approximate location in the sky at 9pm in early March (see A-30 in your book) -- rough altitude and azimuth,
star chart (sketch of the pattern of the 6-8 brightest stars that make up the constellation),
name of one of the bright stars,
2-3 sentence summary of the mythology behind the constellation.

(71)

Why are cool, dense interstellar clouds called "molecular clouds"?

(72)

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.

(73)

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.

(74)

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?

(75)

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)

(76)

During the main sequence lifetime of the star and especially near the end of this main sequence phase, the size of the star slowly increases. Explain why this occurs (two processes contribute).

(77)

Why do giant stars turn red during the latter part of their lives, even though their cores are burning at a somewhat hotter temperature?

(78)

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.

(79)

What is a planetary nebula? Why do some stars undergo this process after the end of the main sequence while other stars avoid it? What causes the nebula?

(80)

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?

(81)

Search the web to find out about "blue stragglers". What are they, and why do they evolve differently from ordinary stars (what causes them to "straggle")? (TQ)

(82)

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?

(83)

Read the article by Jocelyn Bell at http://www.bigear.org/vol1no1/burnell.htm and answer the following: What is Jocelyn Bell's historical significance? Describe how pulsars were discovered. What made us think they might be signals from aliens? How was this hypothesis tested and what was the result?

(84)

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)

(85)

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)

(86)

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?

(87)

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.

(88)

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.

(89)

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

(90)

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."

(91)

What are tidal forces? Why can black holes exert much stronger tidal forces on some objects compared to, say, stars?

(92)

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

(93)

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

(94)

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?

(95)

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, orange or yellow.

(96)

Occasionally, there are both gas clouds and stars in the halo. Explain why the gas clouds eventually became part of the disk while clusters and stars remain in the halo.

(97)

Explain why the spiral arms are so much brighter than the rest of the disk.

(98)

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)?

(99)

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. This is not required, but for more about dark matter, including a description of other ways to detect it, and also a preview of some of the issues we will discuss regarding cosmology, I recommend to you this article by Vera Rubin, one of the pioneering Astronomers who first discovered dark matter.

(100)

Explain gravitational lensing and how it is used to detect planet-sized chunks of dark matter. Why does a planet (or "MACHO") intervening along the line of sight to star cause the star to brighten rather than dim?

(101)

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).

(102)

Explain how we try to estimate how much of the dark matter in our galaxy consists of planetary objects? What conclusion have Astronomers reached about the fraction of the dark matter that consists of planets?

(103)

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)

(104)

Why does it look like we will be unlikely to look for solitary black holes (a dark matter candidate) via lensing in the near future? Explain.

(105)

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.

(106)

Be able to answer questions about Cepheid distance determination, such as: "Compare the light curves of two Cepheids (for example, where the period of star A is twice as long as the period of star B). Which Cepheid is more luminous? If both stars have the same apparent luminosity, which is further away?" (TQ)

(107)

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?

(108)

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.

(109)

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.

(110)

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.

(111)

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?

This is optional but recommended. Read this article by Wendy Freedman, the lead investigator on the Hubble Space Telescope project to measure Cepheids in distant galaxies. In it, she talks about some distance determination methods we will discuss in class and also about the larger cosmological issues we will explore in part 3 of the course. It is some good background for the issues we are currently studying, providing some context for why distance determination is important to cosmology.

(112)

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. How is the rotation velocity of a distant galaxy determined?

(113)

Explain why the TF relation is distance limited (describe the role played by the galaxy's tilt in the method). In other words, why doesn't it work as a distance determination technique beyond a certain distance from the Earth?

(114)

Explain the role that parallax and the Cepheid distance determination technique played in figuring out the absolute luminosities of Type Ia supernovae, which were then used to generate Hubble's Law.

(115)

What is Hubble's Law? Explain how it can be used to determine the distance to a galaxy. How is the radial velocity of a distant galaxy determined?

(116)

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 (especially their structure and the gas/dust content) with the merger hypothesis.

(117)

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.

(118)

Define metal and metallicity. How and why does the metallicity of the galaxy change over time? How does the metallicity of a main sequence star change over time? Explain.

(119)

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)?", "Star X is a blue main sequence star, and star Y is a red main sequence star. Which has a higher metallicity, X or Y (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)

Explain how galaxy motions in clusters are used as evidence for the existence of dark matter.

(122)

Explain how the gravitational lensing of distant galaxies by nearby galaxy clusters is used as evidence for the existence of dark matter.

(123)

How do we know that quasar light does not come from typical stars or galaxies?

(124)

Explain how we know that quasars 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?

(125)

How do we know that quasars have small sizes compared to galaxies? Explain fully (don't just say "because of their timescale of variability" or something ... explain that whole concept).

(126)

Explain what the Copernican Principle is. If we were to study the 10,000 galaxies in our local neighborhood, explain how their properties would likely compare to the 10,000 galaxies in the vicinity of a quasar (in the present day).

(127)

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.

(128)

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?

(129)

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)

(130)

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)

(131)

Three of the most easily recognizable constellations that are up in the sky at this time of year are Leo, Hercules, and Cygnus. Find the following information about these three constellations:

Approximate location in the sky between midnight and 1am in May (see A-31 in your book) -- rough altitude and azimuth,
star chart (sketch of the pattern of the 6-8 brightest stars that make up the constellation),
name of one of the bright stars,
2-3 sentence summary of the mythology behind the constellation.

(132)

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) from the TCU library website, but this is not required.

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.

(133)

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

(134)

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.

(135)

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.

(136)

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.

(137)

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?

(138)

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

(139)

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.

(140)

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.

(141)

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 140 leads us to believe that there may be indeed be some form of cosmological constant?

(142)

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? The metallicity of a star affects how quickly it burns its nuclear fuel. Explain why. If a star has a lower metallicity than we think, how and why will that affect the age estimate for that star? Explain why the Hipparcos satellite measurements resulted in younger age estimates for globular clusters. (TQ)

How to find the article referenced below online:

(1) Go to www.lib.tcu.edu.

(2) In the "Online Catalog Search" box, change the selector from "Words Anywhere" to "Journal/Serial Name Begins With..."

(3) Type "Sciencitic American" (without quotes) into the search box and press the "Search" button.

(4) On the search results page, click on the top listing, which reads "*SCIENTIFIC AMERICAN*"

(5) On records page, click on the first "Full text available" link that you see under detail record 1.

(6) Now you are on the database page for Scientific American Online. In the Find box, type "rip van twinkle" and hit "Search".

(143)

Read the article "The First Stars in the Universe" (Scientific American Special Edition, September 2004), searchable with the phrase "First Stars", 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?

(144)

How is the cosmic background radiation (CBR) related to the big bang?

(145)

Who predicted the existence of the CBR? Who first discovered/observed the CBR?

(146)

Why must we observe the CBR from above the Earth's atmosphere?

(147)

Why are major experiments like the rocket-borne experiment typically performed largely by graduate students rather than professional engineers and scientists?

(148)

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?

(149)

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?

(150)

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?

(151)

Explain what the critical density is. If gravity is the only large-scale force in the Universe, explain how and why the fate of the Universe depends on the density of the Universe and how it compares to the critical density.

(152)

Explain why the observation of the CBR was so significant in the process of the Big Bang theory becoming the "conventional wisdom" of the scientific community. Explain how the observation of the CBR was different from Hubble's discovery in terms convincing scientists.

This is optional, but if you would like to read more about the CBR without opening a Scientific American PDF, the web site from NASA's latest CBR explorer, the Wilkinson Microwave Anisotropy Probe (WMAP) is a good place to start.

(153)

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.

(154)

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.

(155)

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.

(156)

Explain why, in spite of the apparent contradiction between the ages of the oldest stars and the "Hubble age" of the Universe, Astronomers did not abandon the Big Bang theory despite the inconsistency. Ultimately, as explained in 142, this problem was worked out.

(157)

Explain the horizon problem and how the theory of inflation resolves the problem.

(158)

Explain why the inflationary theory predicted a "flat" universe. Explain the terms "flat", "open" and "closed" with respect to the density of the Universe and the critical density.

(159)

Read the first part of this online article from Sky and Telescope about SETI: http://skyandtelescope.com/printable/resources/seti/article_251.asp. Then answer the following: Why is the band of frequencies between 0.5 and 60 Gigahertz the best part of the radio spectrum in which to search for signals?

(160)

Read this article about SETI: http://skyandtelescope.com/printable/resources/seti/article_246.asp and answer the following: Why do the authors think that SETI signals are likely to come from a few very powerful sources (detectable easily with all-sky surveys) rather than from lots of faint sources (detectable with targeted, very sensitive surveys)?

(161)

Read this article about SETI: http://skyandtelescope.com/news/article_1712_1.asp and answer the following: Describe the arguments in favor of Optical SETI searches and why other civilizations might try to use optical wavelengths instead of radio to communicate with us.

(162)

What does it mean to say that we are communicating with extraterrestrials already? What do our signals sound like at various distances from the Earth? Explain.

(163)

Why do radio wavelengths work as the best way to communicate with potential extraterrestrials?

(164)

What is the Fermi paradox, and what is one possible response?

(165)

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?

(166)

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.

(167)

How and why does the lifetime of a civilization relate to the probability that we are not alone?