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Friday, July 6, 2007

The Moon

The Moon (238,857 is Earth's only natural satellite. The average center-to-center distance from the Earth to the Moon is 384,403 kilometresmiles), which is about 30 times the diameter of the Earth. The Moon has a diameter of 3,474 kilometres (2,159 miles) — slightly more than a quarter that of the Earth. This means that the volume of the Moon is only 1/50th that of Earth. Its gravitational pull is about a 1/6th of Earth's. The Moon makes a complete orbit around the Earth every 27.3 days, 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 gravitational attraction, and the centrifugal forces generated by the rotation of the Moon and Earth around a common axis, the barycentre, is largely responsible for the tides on Earth. The energy dissipated in generating tides is directly responsible for the reduction in potential energy in the Moon-Earth orbit around the barycentre, resulting in a 3.8 cm yearly increase in the distance between the two bodies. The Moon will continue to move slowly away from the Earth until the tidal effects between the two are no longer of significance, whereupon the Moon's orbit will stabilize.

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