1) Two bright constellations that are visible in the night sky during April are Hercules and Corona Borealis.

a) (8 pts) Give the approximate location (altitude and azimuth) for these two constellations along with the name of one bright star in each constellation.

b) (6 pts) Suppose the bright star in Hercules is a Cepheid variable. Describe how you could find the distance to that star using the Period-L(abs) relation, step-by-step.

2) One technique we use to search for dark matter is gravitational microlensing, which can occur if a planet-sized object (or very dim star) intervenes along the line of sight to some other distant star.

a) (8 pts) Name two ways we can distinguish between microlensing and other phenomena that can change a star's apparent luminosity. For each feature you mention, explain briefly why ordinary stars differ from lensed stars in this way.

b) (6 pts) In what direction do Astronomers look in order to have the highest probability of observing microlensing, and why?

3) Type Ia supernovae have been the key to accurately determining distances for some of the most distant galaxies visible in the Universe.

a) (8 pts) Briefly explain the difference between type Ia and type II supernovae (maybe one sentence each about how they occur), and explain why type Ia's make such useful standard candles.

b) (6 pts) What role did the Hubble Space Telescope play in developing the Type Ia standard candle method?

4) When Edwin Hubble was first observing and classifying galaxies, he mistakenly thought of elliptical galaxies as "early types" which would later evolve into "late type" spirals. We now have a better idea of why there are two main types of galaxies, and it is called the merger hypothesis.

a) (8 pts) Briefly state what the merger hypothesis is and explain two pieces of evidence (there are many) in support of this hypothesis.

b) (6 pts) Based on the merger hypothesis, if you compare the ratio of spiral galaxies to elliptical galaxies nearby vs the ratio several billion light years away, at which distance (nearby or far away) would you expect to see more spiral galaxies and why?

5) As we look further and further away toward the edge of the visible Universe, we are able to determine what things we like long ago, even tracking the history of star formation in the Universe.

a) (5 pts) Explain why we think it was much harder for stars to form during the first billion years or so compared to today.

b) (5 pts) Describe how the presence of metals made star formation much more efficient after the first generation of stars had completed its life-cycle.

c) (4 pts) At this large distances, distance-determination techniques like the Tully-Fisher relation don't work well. Explain why.

6) Among the most distant sources of light we can see in the Universe are quasars, gamma-ray bursters (GRB's) and the cosmic background radiation (CBR).

a) (4 pts) Describe the evidence that tells us quasars are incredibly distant from Earth.

b) (4 pts) Describe the evidence that tells us GRB's are incredibly distant from Earth (provide a different reason than the one you discussed in part a).

c) (6 pts) The CBR is the most distant observable thing in the Universe. Name and briefly explain what it proves about the nature of the Universe long ago.

7) Within the past 50 years, two major additions have been made to the Big Bang theory. One is the existence of the Cosmic Background Radiation (CBR) and another is the idea of an inflationary Universe at very early times.

a) (8 pts) Explain the "flatness problem" in cosmology, and describe how the theory of inflation resolves this problem.

b) (6 pts) What is different about the CBR evidence compared to Hubble's Law? Briefly explain why the CBR is more important for the validity of the Big Bang theory.

8) Astronomers had hoped to use Hubble's Law to determine the overall density of the Universe, but instead, it seems to show that there is some sort of Cosmological Constant (CC) present in the Universe.

a) (8 pts) Why did Einstein originally introduce the idea of a CC into his theory of cosmology? Why did he later withdraw it?

b) (6 pts) Explain how we can successfully estimate the density of the Universe by analyzing the abundances of Hydrogen and Helium in the Universe.