1. Name and describe the three types of binary systems.
2. Why do most known visual binaries have relatively long periods and most spectroscopic binaries have relatively short periods?
3. Are supergiant stars also extremely massive? Explain the reasoning behind your answer.
4. Suppose you have discovered a new cepheid variable star. What steps would you take to determine its distance?
5. What would be the advantage of making parallax measurements from Pluto rather than from Earth? Would there be a disadvantage?
6. Which of the following can you determine about a star without knowing its distance, and which can you not determine: radial velocity, temperature, apparent brightness, or luminosity? Explain.
7. What causes reddening of starlight? Explain how the reddish color of the Suns disk at sunset is caused by the same process.
8. We can detect 21-cm emission from other galaxies as well as from our own Galaxy. However, 21-cm emission from our own Galaxy fills most of the sky, so we usually see both at once. How can we distinguish the extragalactic 21-cm emission from that arising in our own Galaxy? (Hint: Other galaxies are generally moving relative to the Milky Way.)
9. Suppose that you gathered a ball of interstellar gas that was equal to the size of Earth (a radius of about 6000 km). If this gas has a density of 1 hydrogen atom per cm3 , typical of the interstellar medium, how would its mass compare to the mass of a bowling ball (5 or 6 kg)? How about if it had the typical density of the Local Bubble, about 0.01 atoms per cm3 ? The volume of a sphere is V = 4 3
10. Why are star clusters so useful for astronomers who want to study the evolution of stars?
11. Suppose you were handed two HR diagrams for two different clusters: diagram A has a majority of its stars plotted on the upper left part of the main sequence with the rest of the stars off the main sequence
12. Explain how an HR diagram of the stars in a cluster can be used to determine the age of the cluster
