1) When we plot the radial velocities of galaxies against their redshifts, we come up with a graph like the one shown below (Hubble¹s Law).

a) (2 pts) Which of the three labeled galaxies is most likely to be a spiral galaxy?

b) (12 pts) Explain your answer to (a).

2) The graph below represents the observed abundances of some unknown material in galaxies plotted versus (the very large) distances to the galaxies in question.

a) (3 pts) Is this material something that (increases, decreases, stays the same, can't tell) as the Universe grows older?

b) (3 pts) What element might this material be (there may be more than one possible answer)?

c) (8 pts) Explain your answer to (b).

3) Quasars are incredibly distant and extremely luminous objects (usually 1,000 times more luminous than an entire galaxy) that have a size roughly equal to that of our own solar system. Name and explain the observational evidence that demonstrates that quasars have a small size (small relative to the size of a galaxy, at least).

4) One of the first observations in cosmology was the dark night sky. Although everyone knew this, few people thought of the implications.

a) (7 pts) How does the observation of the dark night sky lead us to believe that the Universe is finite in some way (either space or time)? Explain.

b) (7 pts) Even given a finite Universe of the size observed today, the sky would still be fairly bright from the light of distant sources if it weren¹t for the expansion of the Universe. Explain how the Hubble expansion contributes to the dark night sky.

5) Draw a Hubble¹s Law diagram for a Universe that is not expanding, and explain how and why it is different from the Hubble diagram we observe today. Then draw a Hubble¹s Law diagram for a Universe that is contracting and explain how and why it is different from what we observe.

6) Suppose we lived in a Universe in which the matter density is only about 2% of the critical density rather than what we observe today, which is 20% of the critical density. How would you expect the Helium abundance in this alternate Universe to compare to the Helium abundance in our own Universe (larger, smaller, about the same). Explain your answer.

7) According to optimistic estimates of the quantities in the Drake Equation, some Astronomers believe that the galaxy may hold numerous technologically advanced civilizations capable of communicating with us. However, these assumptions bring up the Fermi Paradox. Explain what the Fermi Paradox is and two possible resolutions or explanations that would resolve the paradox.

8) Two factors in the Drake equation are fL (fraction of suitable planets on which life develops) and L (lifetime of an average civilization).

a) (7 pts) How will current research of Mars and Jupiter's moon Europa affect our estimate of the value of fL? Explain.

b) (7 pts) Why is L relevant in the Drake equation? Explain.