Chapter 13 Vocabulary

2. life cycle, a star is called a
4. stars begin as a large cloud of gas and dust called a
6. an arrangement of stars in the sky
8. heavier and heavier elements form by fusion, and the star expands into a
10. the gravity near this mass is so strong that nothing can escape from it, not even light
12. areas of the Sun’s surface that appear dark because they are cooler than surrounding areas are called
13. the lowest of the Sun's layers and the one that gives off light
14. this is the largest layer of the Sun’s atmo-
15. this causes the outer layers of the star to expand and cool, in this late stage of
16. a large group of stars, gas, and dust held together by gravity
17. this layer extends upward about 2,000 km above the photosphere
18. and extends millions of kilometers into space

1. according to this theory, approximately 13.7 billion years ago,the universe began with an enormous explosion,the entire universe began to expand everywhere at the same time
3. it is a measure of the amount of light received on Earth
5. a measure of the amount of light it gives off
7. only neutrons can exist in the dense core, and it becomes a
9. this leaves behind the hot, dense core, at this stage in a star’s evolution, it becomes a
11. the distance that light travels in one year