| A | B |
|---|
| light-year (ly) | the distance that light travels in one year |
| astronomical unit | a unit of length that equals the average distance from the sun to the earth |
| atmosphere | the layer of air that surrounds the earth |
| hydrosphere | the layer of water that covers the earth |
| lithosphere | the solid surface of earth |
| rotation | the turning of an object on its axis |
| revolution | the movement of an object along an orbit, or path, around another body |
| craters | round depressions on the moon's surface |
| phases | the different shapes that the moon appears to have |
| eclipse | occurs when one object is in the shadow of another |
| luner eclipse | occurs when the moon passes through the shadow of earth |
| solar eclipse | occurs when the earth passes through the moon's shadow |
| nebula | a cloud of gas and dust |
| nebular hypothesis | a hypothisisof the orgin of our solar system, stating that it formed from a cloud of dust and gas |
| protostar | matter in a nebula that pulled towards the center |
| protoplanet | whirlpools of matter, which formed the bodies of the solar system |
| constellation | a group of stars that forms a pattern or picture in the sky |
| refracting telescope | a telescope which uses a lens to gather light and form an image |
| reflecting telescope | a telescope that uses a mirror to gather light and form an image |
| radio telescope | a giant antenna and dish used to gather radio waves given off by stars |
| appearant magnitude | the brightness of an object as viewed from earth |
| absolute magnitude | a measure of the star's true brightness |
| Hertzsprung-Russel Diagram | graph that shows the relationship between absolute magnitude and temperature of stars |
| Main Sequence Stars | stars that appear on the main sequence of the H-R diagram |
| red giant | a cool, red star that appears very bright because of its large size |
| white dwarf | a hot star that does not appear very bright because of its small size |
| supernova | the violent explosion of a large star near the end of its life |
| galaxy | a large group of stars |
| big bang theory | the universe, with its matter, energy, and forces was formed when an explosion occurs |
