| 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 about its axis. |
| revolution | The movement of an object around another object. |
| latitude | The distance north or south from the equator, measured in degrees. |
| solstice | The two days of the year on which the noon sun is directly overhead at either 23.5° South or 23.5° North. |
| equinox | The two days of the year on which neither hemisphere is tilted toward or away from the sun. |
| vernal equinox | The day of the year that marks the beginning of spring in the Northern Hemisphere. |
| autumnal equinox | The day of the year that marks the beginning of fall in the Northern Hemisphere. |
| phase | One of the different shapes of the moon as seen from Earth. |
| eclipse | The partial or total blocking of one object by another. |
| solar eclipse | The blocking of sunlight to Earth that occurs when the moon is 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 moon. |
| tides | The daily rise and fall of Earth's waters on shores. |
| gravity | The attractive force between two objects; its magnitude depends on their masses and the distance between them. |
| satellite | Any object that revolves around another object in space. |
| geosynchronous orbit | The orbit of a satellite that revolves around Earth at the same rate that Earth rotates. |
| telescope | A device built to study distant objects by making them appear closer. |
| crater | A bowl-shaped area that forms around a volcano's central opening; A round pit on the moon's surface. |
| maria | Dark, flat regions on the moon's surface once thought to be the remainders of seas. |
