Questions for Review


1		What are the three main types of galaxies?



2		How do the basic galaxy types differ in shape, stellar content, and interstellar matter?



3		Why is it not surprising that elliptical galaxies contain only old stars?



4		Which of the basic galaxy types has the smallest proportion of Pop I stars?



5		What happens to the stars when two galaxies collide?



6		Why are galaxy collisions of interest?



7		How do astronomers measure the distance to nearby galaxies?



8		What is the Hubble law?



9		Why are astronomers uncertain about the value of the Hubble constant?



10		How do astronomers measure the mass of a galaxy?



11		What is meant by dark matter?



12		What are the three main types of active galaxies?



13		Make a sketch of a radio galaxy illustrating its structure and where its radio emission comes from. Why do astronomers call these objects “radio” galaxies?



14		What process generates the radio emission in radio galaxies?



15		What is a Seyfert galaxy?



16		What is a quasar?



17		Why do some astronomers think that quasars are very distant?



18		How is it known that active galaxies have small core regions?



19		What mechanism has been suggested to power active galaxies?



20		How might a large black hole form in a galaxy’s core?



21		What is a gravitational lens?



22		What are some differences between rich and poor clusters?



23		What is the Local Group?



24		What is the Local Supercluster?



25		What is a void?

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