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Earth's Place in the
Unit 6
| Term | Definition |
|---|---|
| asteroid | a small, rocky object that orbits the sun |
| astronomical unit | the average distance between Earth and the sun |
| comet | a small body of ice, rock, and cosmic dust that follows an elliptical orbit around the sun and that gives off gas and dust in the form of a tail as it passes close to the sun |
| eclipse | an event in which the shadow of one celestial body falls on another |
| galaxy | a collection of stars, dust, and gas bound together by gravity |
| gravity | a force of attraction between objects that is due to their masses |
| light-year | the distance that light travels in one year |
| orbit | the path that a body follows as it travels around another body in space |
| parallax | an apparent shift in the position of an object when viewed from different locations |
| phase | in astronomy, the change in the sunlit area of one celestial body as seen from another celestial body |
| protoplanetary disk | a disk of gas and dust orbiting a newly formed star, from which planets may eventually form |
| season | a division of the year that is characterized by recurring weather conditions and determined by both Earth’s tilt relative to the sun and Earth’s position in its orbit around the sun |
| solar nebula | a rotating cloud of gas and dust from which the sun and planets formed |
| telescope | an instrument that collects light from distant objects and concentrates it to make the objects appear larger or brighter |
| universe | space and all the matter and energy in it |