| Word | Definition |
| 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. |
| Tide | The rise and fall of the level of water in the ocean. |
| Gravity | The attractive force between two objects; its magnitude depends on their masses and the distance between them. |
| Spring tide | A tide with the greatest difference between low and high tides. |
| Neap tide | A tide with the least difference between low and high tides. |
