Unit 6: Lesson 7: The Universe Assessment Questions

How do galaxies differ?

Galaxies differ in size, shape, and the ages of their stars.

What is a galaxy?

A galaxy is a large group of stars, dust, and gases held together by gravity.

If the universe is an open universe, what can you infer about its average density?

Its average density must be less than its critical density.

Describe the size and structure of the Milky Way Galaxy.

The Milky Way is a large spiral galaxy whose disk is about 100,000 light-years wide and about 10,000 light-years thick at the nucleus.

What is the big bang theory?

The big bang theory states that about 13.7 billion years ago, the universe began at one point and has been expanding ever since.

Compare and contrast the three types of galaxies.

The most obvious difference is their shape: spiral galaxies have arms; elliptical galaxies range in shape from round to oval; irregular galaxies have no regular shape. Irregular galaxies are composed mostly of young stars, while elliptical galaxies contain mostly older stars. Spiral galaxies are composed of stars of various ages, with the youngest stars in the arms.

What evidence indicates that the universe is expanding?

The red shifts of distant galaxies indicate that the universe is expanding.