| A | B |
|---|
| Planet | An object that orbits a star, is large enough to have become rounded by its own gravity, and has cleared the area of its orbit. |
| Meteor | A streak of light in the sky produced by the burning of a meteoroid in Earth’s atmosphere. |
| Comet | A loose collection of ice and dust that orbits the sun, typically in a long, narrow orbit. |
| Star | A ball of hot gas, primarily hydrogen and helium, that undergoes nuclear fusion. |
| Force | A push or pull exerted on an object. |
| Gravity | The attractive force between objects; the force that moves objects downhill. |
| Inertia | The tendency of an object to resist a change in motion. |
| Mass | A measure of how much matter is in an object. |
| Weight | A measure of the force of gravity acting on an object. |
| Rotation | The spinning motion of a planet on its axis. |
| Revolution | The movement of an object around another object. |
| Orbit | he path of an object as it revolves around another object in space. |
| Solstice | Either of the two days of the year on which the sun reaches its greatest distance north or south of the equator. |
| Equinox | Either of the two days of the year on which neither hemisphere is tilted toward or away from the sun |
| Solar eclipse | The blocking of sunlight to Earth that occurs when the moon is directly between the sun and Earth. |
| Umbra | The darkest part of a shadow. |
| Penumbra | The part of a shadow surrounding the darkest part. |
| Lunar eclipse | The blocking of sunlight to the moon that occurs when Earth is directly between the sun and the moon. |
| Meteoroid | A chunk of rock or dust in space, generally smaller than an asteroid. |
| Maria | Dark, flat areas on the moon’s surface formed from huge ancient lava flows. |
