| A | B |
|---|
| astronomical unit (AU) | The average distance between the Earth and the sun, or approximately 150,000,000 km. |
| terrestrial planets | The small, dense, rocky planets of the inner solar system. |
| prograde rotation | the counter-clockwise spin of a planet or moon as seen from above the planet's north pole. |
| retrograde rotation | the clockwise spin of a planet or moon as seen from above the planet's north pole. |
| gas giants | The large, gaseous planets of the outer solar system. |
| satellite | A natural or artificial body that revolves around a planet. |
| phases | The different appearances of the moon due to varying amounts of sunlight on the side of the moon that faces the Earth; results from the changing relative positions of the moon, Earth, and the sun. |
| eclipse | An event in which the shadow of one celestial body falls on another. |
| comet | A small body of ice, rock, and comet dust loosely packed together that gives off gas and dust in the form of a tail as it passes close to the sun. |
| asteroid | a small, rocky body that revolves around the sun. |
| asteroid belt | The region of the solar system most asteroids occupy; roughly between the orbits of Mars and Jupiter. |
| meteoroid | A very small, rocky body that revolves around the sun. |
| meteorite | A meteoroid that reaches the Earth's surface without burning up completely. |
| meteor | A streak of light caused when a meteoroid or comet dust burns up in Earth's atmosphere before it reaches the ground. |
