Ch. 16/17 Test

5. a group of stars, dust, gas, and other objects held together by gravitational forces
6. the first stage in the life cycle of a star
7. a huge cloud of dust and gas from which stars form
8. a method of studying an object by examining the visible light and other electromagnetic waves it creates
12. galaxy the spiral galaxy to which our solar system belongs
13. measures the amount of light reaching Earth
14. a large star with low temperature and high brightness
15. the total amount of light given off by a star
16. fusion reactions which combine light elements such as hydrogen into heavier elements such as helium, releasing energy

1. year the distance light travels through space in one year
2. theory that the universe began as a huge explosion 10 billion to 20 billion years ago
3. an enormous hot ball of gas held together by gravity which produces energy through nuclear fusion reactions in its core
4. sequence star a stable star in the main category in the H-R diagram
6. the expanding outer shell of a sunlike star. This matter is blown away as the core shrinks to become a white dwarf
8. very large, bright star that may be blue or red, depending on its temperature
9. the explosion of a very large star
10. a small star with a high temperature and low brightness
11. a system of two stars orbiting each other that are gravitationally tied together