| A | B |
|---|
| geocentric | A description of the solar system in which all of the planets revolve around Earth. |
| heliocentric | A description of the solar system in which all of the planets revolve around the sun. |
| ellipse | An elongated circle, or oval shape; the shape of the planets' orbit |
| inertia | The tendency of a moving object to continue in a straight line or a stationary object to remain in place. |
| terrestrial planet | The name given to the four inner planets: Mercury, Venus, Earth, and Mars. |
| retrograde rotation | The spinning of a planet from East to West, opposite to the direction of rotation of most planets and moons. |
| greenhouse effect | The trapping of heat by a planet's atmosphere. |
| gas giant | The name given to the first four outer planets: Jupiter, Saturn, Uranus, and Neptune. |
| comet | A ball of ice and dust whose orbit is a long, narrow ellipse. |
| asteroid | Objects revolving around the sun that are too small and too numerous to be considered planets. |
| asteroid belt | The region of the solar system between the orbits of Mars and Jupiter, where many asteroids are found. |
| meteoroid | A chunk of rock or dust in space. |
| meteor | A streak of light in the sky produced by the burning of a meteoroid in the Earth's atmosphere. |
| meteorite | A meteroid that has hit Earth's surface. |
