1) Below is a simple version of the graph used in the Hubble Law distance determination method. Recently, Astronomers have looked for deviations from this simple "constant expansion" case to try to come to some conclusions about the overall density of the Universe and/or the expansion rate. Assume for this question that there is no cosmological constant, no accelerating force in the Universe.

How would a low density (but not zero density) Universe look compared to the "constant expansion" case? Indicate your answer by altering the graph below (if the graph doesn't need to be altered, just write "no change" on the graph). Next to the graph, explain why you changed (or didn't change) the graph in the way you did.

2) An Astronomer is observing a bright star in Canis Minor and trying to find the details about its properties.

a) (7 pts) What is the approximate location (altitude and azimuth) of Canis Minor in the sky tonight at around 10pm? Also, what is the name of a bright star in that constellation?

b) (7 pts) Suppose that bright star happens to be a Cepheid variable. Describe step-by-step how you would determine the distance to that star using the Cepheid Period-Luminosity relation, assuming no interstellar material is along your line of sight to the star.

3) Below is a Keplerian rotation curve (the kind that would be suitable for describing the motion of planets in our solar system) for reference. Prior to the discovery of dark matter, Astronomers measured the rotation of the Milky Way, hoping to plot the data on a graph similar to this one (but not necessarily following the Keplerian curve).

On the graph below, draw the kind of data Astronomers expected to find for our galaxy in the absence of dark matter. If it would be a Keplerian curve, just write "same" on the graph. Next to the graph, explain your answer in detail (if it is different, explain why your graph is different ... if it is the same, explain why the galaxy rotates in exactly the same way as our solar system despite being much larger, etc).

4) When the Milky Way galaxy first collapsed into a disk, it took a long time for the spherical proto-galactic cloud to assume its final shape, with a gas-rich disk and a spherical halo of stars and star clusters.

a) (7 pts) The halo, like the rest of the initial cloud, had a mix of stars, gas and dust. Explain why, soon after the galaxy formed, the halo largely consisted of stars only.

b) (7 pts) In general, light from the region of the galactic halo is red. Explain why.

5) Quasars are a relatively recent discovery. These extremely bright objects are the most distant objects observed in our Universe.

a) (7 pts) Name and explain the observational fact that tells us quasars have an extremely small size compared to galaxies like our own.

b) (7 pts) Astronomers think that quasars may be the central bright regions of newly forming galaxies. If we were to observe the composition of the gas in these "galaxies" at such great distances from the Earth (8-10 billion) light years, how would you expect the Hydrogen abundance of these objects to compare to the Hydrogen abundance of today's galaxies? Explain your answer.

6) Some of the most distant objects known, besides quasars, are Gamma-Ray Bursters (GRB's).

a) (6 pts) Name and briefly explain the evidence that tells Astronomers GRB's are not nearby or within our own galaxy.

b) (8 pts) At such large distances, Astronomers often use the Standard Candle (SC) method of distance determination, using our galaxy's own luminosity as a standard. Explain why the SC method used in this way is not accurate, then describe how to improve the technique while still using galaxies as your "standard" (and explain why this change improves the accuracy of the technique). Note that I'm not asking about supernovae here.

7) Long ago, when Astronomers thought the Universe was infinite in space and time, Albert Einstein proposed the existence of a "cosmological constant" (CC) to explain his observations of the Universe.

a) (7 pts) Explain briefly why Einstein felt it was necessary for the Universe to have a CC and then why he later retracted his claim and said a CC wasn't needed.

b) (7 pts) Describe the evidence that tells us today there must be some sort of CC in the Universe.

8) When we look with our optical telescopes at the night sky, we see mostly darkness in all directions. This leads us to conclude something very important about the Universe as a whole. When we look for extraterrestrial signals with our radio telescopes at the sky, we see no intelligent signals in any direction. This also leads to some interesting conclusions.

a) (7 pts) What does the dark night sky proves about the nature of the Universe? Explain fully why the dark night sky proves this.

b) (7 pts) Some Astronomers have concluded that we should look for extraterrestrial intelligence signals in optical rather than radio wavelengths. Explain why they think it might be better (aside from the fact that we haven't seen anything with radio yet) to look in this wavelength region of the spectrum.