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

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

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

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

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

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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?

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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?

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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?

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.

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Two of the most easily recognizable constellations that are up in the sky at this time of year are Canis Major and Auriga. Find the following information about these two constellations:

• Approximate location in the evening sky this month, based on the star chart on page A-32 (rough altitude and azimuth),
• star chart (sketch of the pattern of the 6-8 brightest stars that make up the constellation),
• name of the two stars designated alpha and beta (usually the two brightest),
• 2-3 sentence summary of the mythology behind the constellation.

Remember the links: for mythology it is http://www.emufarm.org/~cmbell/myth/myth.html. For simple star charts, it is http://www.dibonsmith.com/constel.htm (but I would prefer you use the back of your book star chart given above). For star names and other information, try http://www.astro.wisc.edu/~dolan/constellations/. (TQ)

The following study guide questions are based on the Scientific American article, "The First Stars in the Universe", from the September 2004 Special Edition of Scientific American:

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What are "Population III" stars? How and why are these stars linked to the appearance of quasars? (TQ)

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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, the minimum mass needed for a cloud to collapse into a star, larger long ago)? (TQ)

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Why was the second generation of star formation more efficient than the first generation, which took a lot longer to form (what did metals have to do with it)? (TQ)

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Early in the history of the Universe, most of the gas became ionized. What caused this? (TQ)

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Explain the relationship between age and color for individual stars. Are blue main sequence stars young? Explain. Are red main sequence stars old? Explain.

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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.

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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?

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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)?"

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More examples of age/metallicity questions: "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)?"

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How does the metallicity of an older galaxy compare to the metallicity of a younger galaxy? Explain.

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

The following questions are from the Scientific American article "Rip van Twinkle" published in the May 2001 issue.

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What is the "age crisis" in terms of cosmology, and how was it resolved? (TQ)

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What evidence indicates that globular clusters are probably the oldest parts of our galaxy? Explain. (TQ)

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The metallicity of a star affects how quickly it burns its nuclear fuel. Explain why. (TQ)

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Explain why the Hipparcos satellite measurements resulted in younger age estimates for globular clusters. (TQ)

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Explain how the coronal gas in galaxy clusters is used as evidence in favor of the existence of dark matter.

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

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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?

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How do we know that quasars, despite being brighter than typical galaxies, have sizes that are more like the size of our solar system (a few light-days across instead of hundreds of thousands of light years).

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Describe the distribution of quasars in the sky. Does this violate the Copernican Principle? Explain your answer. Why are the quasars distributed in this way?

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Why do we think QSO's are powered by massive black holes (two lines of evidence)?

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Why do we think QSO's are an early stage in the evolution of galaxies (two things quasars and galaxies share in common)?

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

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

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What does the existence of the CBR prove about the nature of the Universe long ago? Explain.

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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.

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Be able to plot a graph of a race at various times as we did in lecture given some basic data. Given a graph of a race, be able to find the slope of the graph and the age of the race.

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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.

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If Astronomers had been alive back when the Universe was only about 5 billion years old and tried to plot a Hubble diagram, would it have looked the same back then as it does now? Explain, keeping in mind the car race analogy we did in class.

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Why is it that some galaxies do not appear to be moving away from us? Why are all such galaxies relatively close to us? Does that mean Hubble's Law is not valid? Why not?

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

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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 why they differ.

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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.

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Explain what the Cosmological Constant is. Why did Einstein originally introduce the idea of a Cosmological Constant? Why was it later abandoned?

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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.

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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.

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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.

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