| A | B |
|---|
| solar system | made of sun |
| orbit | elliptical path a body takes around another body in space |
| period of rotation | time for a body to spin once on its axis |
| period of revolution | time for a body to complete an orbit around another body |
| astronomical unit | average distance from the Earth and the sun |
| terrestrial planets | small dense rocky planets of the inner solar system |
| gas giant | large gaseous planets of the outer solar system |
| satellite | natural or artificial body that revolves around a planet |
| eclipse | when a shadow of one celestial body falls on another |
| nebula | location of star formation |
| comet | small body of ice and rock |
| asteroid | small rocky body that revolves around the sun |
| asteroid belt | found between the orbits of Mars and Jupiter |
| meteoroid | very small rocky body that revolves around the sun |
| meteorite | meteoroid that reaches the EarthÂ’s surface before burning up |
| meteor | streak of light caused when it burns up in the EarthÂ’s atmosphere |
| light-year | equal to the distance that light travels in a year |
| white dwarf | small hot star near the end of its life |
| red giant | star that expands and cools once it runs out of hydrogen |
| supernova | death of a large star by explosion |
| black hole | object whose gravity is so strong that light cannot escape |
| galaxy | large grouping of stars |
| spiral galaxy | has a nuclear bulge in the center with distinctive spiral arms |
| elliptical galaxy | spherical or elongated with a bright center and very little dust and gas |
| irregular galaxy | galaxy that does not fit any other catergory |
| big bang theory | states that the universe began with a tremendous explosion |
