Vocabulary Review

2. Includes all of space, and all of the matter and energy that space contains.
5. The spinning motion of a planet on its axis.
7. A ball of frozen dust and rock that orbits the sun and has a tail that glows.
8. Natural force that causes things to fall toward the Earth.
9. A relatively small, rocky body that moves through space.
12. A chemical element that is is the simplest and lightest of all chemical elements.
14. A large body in space that orbits a star and does not produce light of its own.
15. The path of an object as it revolves around another object in space.
18. The gas found between stars which is mostly comprised of hydrogen and helium scattered between stars.
20. The theory that all matter and energy in the universe was compressed into an extremely small volume that 13 to 15 billion years ago exploded and began expanding in all directions.
22. The movement of distant galaxies and other objects away from an observer, causing the wavelength of light to stretch towards the red end of the visible light spectrum.
23. Laws describing the motions of the planets and other objects in the solar system.
24. These are the planets, closest to the sun, are small, made of rock and metal.

1. The cooled remnant of the first light that ever travel freely throughout the universe.
3. The study of the moon, stars and other objects in space.
4. Large round object that circles a planet and shines at night by reflecting light from the Sun.
6. A chemical element that is light, colorless, nonflammable and found in natural gas.
8. A system of millions or billions of stars, gas and dust, held together by gravity.
10. These planets are, farther away from the sun, are very large, made of gas and liquid.
11. A huge collection of stars, dust and gas which contains our solar system.
13. Anything that takes up space and has mass.
16. A small, rocky object that orbits the sun, mostly located in a band between the orbits of Mars and Jupiter.
17. Any object that self-luminates with hot gasses by an internal energy source.
19. Includes the Sun, all of the planets and other objects bound to it by gravity.
21. Energy in the form of waves of particles moving through space.