| Term | Definition |
| revolve | To travel in a closed path around an object such as Earth does as it moves around the sun. |
| rotate | The spinning of Earth on its axis. |
| axis | An imaginary line that passes through the Earth's center and its north and south poles. |
| eclipse | The passing of one object through the shadow of another. |
| ellipse | A streched out circle. It describes Earth's orbit around the sun. |
| gibbous | More than half but not all of the moon is lighted. |
| waxing | The moon becoming more visible. |
| waning | The moon becoming less visible. |
| crescent | The shape of the visible moon during about the first week after new moon or the last week before the next new moon |
| lunar | Anything relating to the moon. |
| maria | A landform on the moon that's dark and flat. They're made of hardened lava. |
| rille | A lunar valley. |