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unit 2 lesson 1 and2
| Term | Definition |
|---|---|
| solar system | the sun and all of the planets and other bodies that travel around it |
| galaxy | a collection of stars dust and gas bound by gravity |
| planet | a relatively large spherical l body that orbit a star |
| light year | the distance that light travels in on year about 9.46 trillion kilometers |
| star | a large celestial body that is composed of gas and emits lighr the sun is a typical star. |
| universe | space and all the matter and energy in it |
| luminosity | the actual brightness of an object such as a star |
| Apparent magnitude | the brightness of a star as see from earth |
| Absolute magnitude | absolute magnitude is a measure of how bright a star would be if it were seen from a standard distance |