Chapter 31

2. the galaxy we live in
4. In about five billion years, our Sun will expand to become this
6. The study of how the universe began, how it continues to change, and what it is made
7. is a large group of stars, dust, and gas held together by gravity
8. names given to these groups of stars by ancient cultures
10. the layer of the Sun that emits light
12. uses a prism or diffraction grating to separate light
15. About 90 percent of all stars are classified as
16. an area in space that is so dense that nothing can escape

1. the distance light travels in one year
3. The Milky Way is part of a larger group of galaxies called the
5. collects and amplifies radio waves
9. an invisible form of matter that does not emit any detectable electromagnetic energy of its own
11. Stars form from a large cloud of gas, ice, and dust
13. forms as the core of a giant star no longer supports fusion
14. dark cool areas on the sun