Lunar science Reference Libraries

The Hadean is the unofficial geological period of time that lies just before the Archean time period. The Hadean began with the formation of the Earth roughly 4.5 billion years ago (Ga) and ended about 3.8 Ga; the latter date varies according to different sources. Hadean is derived from Hades, Greek for “underworld,” referring to the hellish conditions on the planet at the time. The term...

Crater -- A crater is a circular depression on the surface of a planet, moon, asteroid, or other celestial body. Craters are typically caused by meteorite impacts, although some are caused by volcanic activity. In the center of craters on Earth a crater lake often accumulates, and in craters formed by meteorites a central island (caused by rebounding crustal rock after the impact) is...

The Moon -- The Moon is the largest satellite of the Earth, and is occasionally called Luna (Latin for moon) to distinguish it from the general use of the word "moon". The Moon is distinguished from the satellites of other planets by its initial capital letter; the other moons are described in the natural satellite article. The words moon and month come from the same Old English root word....

The Moon -- natural satellite of a planet, in particular, the single natural satellite of the earth. The Earth-Moon System The moon is the earth's nearest neighbor in space. In addition to its proximity, the moon is also exceptional in that it is quite massive compared to the earth itself, the ratio of their masses being far larger than the similar ratios of other natural satellites...