| A | B |
|---|
| gravity | The attractive force between two objects; its magnitude depends on their masses and the distance between them. |
| inertia | The tendency of a moving object to continue in a straight line or a stationary object to remain in place. |
| 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. |
| terrestrial planets | The name given to the four inner planets: Mercury, Venus, Earth, and Mars. |
| gas giant | The name given to the first four outer planets: Jupiter, Saturn, Uranus, and Neptune. |
| aurora borealis | A colorful, glowing display in the sky caused when particles from the sun strike oxygen and nitrogen atoms in the ionosphere; also called the Northern Lights. |
| comet | A ball of ice and dust whose orbit is a long, narrow ellipse. |
| meteorite | A meteoroid that has hit Earth's surface. |
| 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 Earth's atmosphere. |
| asteroid | Objects revolving around the sun that are too small and too numerous to be considered planets. |
| retrograde rotation | The spinning motion of a planet from east to west, opposite to the direction of rotation of most planets and moons. |
| chromosphere | The middle layer of the sun's atmopshere. |
| corona | The outer layer of the sun's atmosphere. |
| photosphere | The inner layer of the sun's atmosphere. |
| prominence | A loop of gas that protrudes from the sun's surgace, linking parts of sunspots regions. |
| solar flare | An explosion of hydrogen gas from the sun's surgace that occurs when loops in sunspot regions suddenly connect. |
| solar wind | A stream of electrically charged particles produced by the sun's corona. |
| sunspot | Dark, cooler regions on the surgace of the sun. |
