1. How is 21 cm radiation used by astronomers and what does it tell them?

2. There is an organizational structure to the universe that exists at a level higher than that of the galaxy. Describe this structure?

3. When galaxies merge (collide) do stars actually collide? What are the possible outcomes?

4. How do we know that quasars are not just nearby stars?

5. Just like stars provide the physical force to structure solar systems, black holes provide the physical force to structure galaxies. Is this statement true? Why or why not?