Ch. 16/17 Test

2. Bang theory that the universe began as a huge explosion 10 billion to 20 billion years ago
4. a huge cloud of dust and gas from which stars form
7. year the distance light travels through space in one year
8. sequence star a stable star in the main category in the H-R diagram
9. measures the amount of light reaching Earth
10. the first stage in the life cycle of a star
11. an enormous hot ball of gas held together by gravity which produces energy through nuclear fusion reactions in its core
12. the explosion of a very large star
16. fusion reactions which combine light elements such as hydrogen into heavier elements such as helium, releasing energy
18. a group of stars, dust, gas, and other objects held together by gravitational forces

1. dwarf a small star with a high temperature and low brightness
3. very large, bright star that may be blue or red, depending on its temperature
5. the total amount of light given off by a star
6. a method of studying an object by examining the visible light and other electromagnetic waves it creates
13. nebula the expanding outer shell of a sunlike star. This matter is blown away as the core shrinks to become a white dwarf
14. giant a large star with low temperature and high brightness
15. star a system of two stars orbiting each other that are gravitationally tied together
17. Way galaxy the spiral galaxy to which our solar system belongs