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Luna

The average centre-to-centre distance from the Earth to the Moon is 384,403 km, about thirty times the diameter of the Earth. The Moon's diameter is 3,474 km, a little more than a quarter of that of the Earth. Thus, the Moon's volume is about 2 percent that of Earth; the pull of gravity at its surface is about 17 percent that at the Earth's surface. The Moon makes a complete orbit around the Earth every 27.3 days (the orbital period), and the periodic variations in the geometry of the Earth–Moon–Sun system are responsible for the lunar phases that repeat every 29.5 days (the synodic period).

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Uploaded on Jan 20, 2009

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