| A | B |
|---|
| astronomy | The study of the moon, stars, and other objects in space. |
| axis | An imaginary line that passes through Earth’s center and the North and South poles, about which Earth rotates. |
| rotation | The spinning motion of a planet on its axis. |
| revolution | The movement of an object around another object. |
| orbit | The path of an object as it revolves around another object in space. |
| calendar | A system of organizing time that defines the beginning, length, and divisions of a year. |
| solstice | The two days of the year on which the sun reaches its greatest distance north or south of the equator. |
| equinox | The two days of the year on which neither hemisphere is tilted toward or away from the sun. |
| phases | One of the different apparent shapes of the moon as seen from Earth. |
| eclipse | The partial or total blocking of one object in space by another. |
| umbra | The darkest part of a shadow. |
| penumbra | The part of a shadow surrounding the darkest part. |
| tide | The periodic rise and fall of the level of water in the ocean. |
| spring tide | The tide with the greatest difference between consecutive low and high tides. |
| neap tide | The tide with the least difference between consecutive low and high tides. |
| telescope | A device built to observe distant objects by making them appear closer. |
| maria | Dark, flat areas on the moon’s surface formed from huge ancient lava flows. |
| craters | A large round pit caused by the impact of a meteoroid. |
| meteoroids | A chunk of rock or dust in space. |
