1) This question deals with some of the highest and lowest energy particles observed by Astronomers.

a) (9 pts) What are "fastballs" in the Astronomical sense? Why do we think fastballs must originate from some nearby source? Why do fastballs seems to come in toward Earth from all directions?

b) (5 pts) 21-cm radiation is very important to radio astronomers. What kind of atoms does this radiation come from, and why is it so important for studying the galaxy?

2) Although a star's properties are relatively stable during the main sequence portion of its lifetime, the size does grow somewhat.

a) (7 pts) Why do stars grow in size during the main sequence? Talk about the behavior of Helium and Hydrostatic Equilibrium (HSE) as part of your answer.

b) (7 pts) Explain what the Faint Sun Paradox is. Also explain how the Earth's atmosphere has "resolved" this paradox.

3) Answer the following questions about planetary nebulae (PN):

a) (5 pts) What causes planetary nebulae?

b) (4 pts) What is the origin of the name "planetary nebula"?

c) (5 pts) Why do high-mass stars generally avoid becoming PN?

4) Radio astronomers were responsible for the discovery of pulsars. They often observe at wavelengths similar to what you might pick up on your car radio or walkman.

a) (6 pts) Explain why AM radio signals tend to travel further at night.

b) (8 pts) Explain what a pulsar is and why some objects that are pulsars do not look like pulsars when we observe them from Earth.

5) The galactic center is difficult to study thanks to all the intervening material in the disk of our galaxy, but we have managed to deduce the existence of a large black hole there over 20 million times the mass of our own Sun.

a) (7 pts) Explain how we know there is a black hole at the galactic center.

b) (7 pts) The material surrounding the black hole seems to give off "too little" energy compared with what we expected. Explain what we think caused this situation.

6) Suppose two stars, Spica and Arcturus, have the same spectral line width, but Arcturus' peak wavelength is much longer, giving Arcturus a red color compared to Spica. Assuming there is no interstellar material along the line of sight to either star and that the two stars have the same mass and composition, which star is larger (or are they the same size)? Explain your answer.

7) Suppose we wish to study a bright star in the constellation Auriga. In order to do so, we'll need to correct for any effects of the interstellar medium (ISM) along the line of sight to that star.

a) (8 pts) What is the approximate location (altitude and azimuth) of Auriga at 10pm this evening? Also, what is the name of one of the bright stars in Auriga? Finally, briefly explain (a single sentence will do) what Auriga represents in mythology.

b) (6 pts) Explain how and why spectral lines due to the ISM differ from stellar lines.

8) One way to estimate a star's age is to look at its metallicity.

a) (6 pts) How and why is the metallicity of a star related to its age?

b) (4 pts) If star X has 20x the mass of the Sun, would you expect it to have a higher or lower metallicity compared to the Sun? Or would it be unknown? Explain your answer.

c) (4 pts) If star X has 1/2 the mass of the Sun, would you expect it to have a higher or lower metallicity compared to the Sun? Or would it be unknown? Explain your answer.