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Unit 2: The Universe
| Term | Definition |
|---|---|
| solar system | The sun and all of the planets and other bodies that travel around it. |
| planet | A relatively large spherical body that orbits a star. |
| star | A large celestial body that is composed of gas and that emits light; the sun is a typical star. |
| galaxy | A collection of stars, dust, and gas bound together by gravity. |
| light-year | The distance that light travels in one year; about 9.46 trillion kilometers. |
| universe | Space and all the matter and energy in it. |
| apparent magnitude | The brightness of a star as seen from Earth. |
| luminosity | The actual brightness of an object such as a star. |
| absolute magnitude | Absolute magnitude is a measure of how bright a star would be if it were seen from a standard distance. |