| Term | Definition |
|---|
| Penumbra | Partial shadow where some light is blocked and other light fills in |
| Perigee | Point nearest earth in the moon's orbit |
| Perihelion | Point in a planet's orbit where it is nearest to the sun |
| Ray | Bright streaks of shattered rock and dust that radiate from several moon craters |
| Regolith | Lunar soil, a grayish-brown mixture of small pieces |
| Revolution | The movement of earth in its orbit around the sun |
| Rille | Long, deep cracks runninig through the moon's maria bedrock |
| Rotation | Turning of an object on its axis |
| Solar Eclipse | An eclipse that occurs when the moon's shadow blocks the sun |
| Spring Equinox | First day of spring in the northern hemisphere. |
| Summer Solstice | The first day of summer in the northern hemisphere |
| Umbra | Dark shadow where light is completely blocked |
| Winter Solstice | First day of winter in the northern hemisphere, shortest daylight period |
| Zenith | Point in the sky directly above the observer |
Combine with other sets
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