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==Unusual characteristics of the Moon==

==Unusual characteristics of the Moon==

Unlike most planets{{fact}}, Earth has only one moon and it has several striking characteristics:   

Unlike most planets in the solar system, Earth has only one moon and it has several striking characteristics:   

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|1.

|Throughout man's existence, the Moon has had the same size as the [[Sun]] when viewed from Earth.  This creates a beautiful symmetry and permits phenomenal eclipses to occur. The odds of that symmetry occurring by chance are very small. That symmetry will not last forever.

|During recent history the Moon has had roughly same size as the [[Sun]] when viewed from Earth.  This creates a situation which permits phenomenal solar eclipses to occur. The odds of that symmetry occurring by chance are very small. That symmetry will not last forever.

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|2.

|The Moon presents the same side to Earth at all times, even though the Moon revolves around the Earth.  That requires the rotation of the Moon to be timed precisely to offset the separate effects of the revolution around Earth. Physicists explain this phenomenon by invoking [[tidal locking]]; tidal forces on Earth caused a bulge on the Moon, thereby creating a drag on the rotation of the Moon until its same face always presents to the Earth.  It was once believed that the planet [[Mercury]] had a similar locked rotation due to gravitational forces from the sun, such that the same side of Mercury always faces the sun. In fact, Mercury's tidal locking is incomplete; it does not always present the same face to the sun, but rather switches the side that it presents to the sun every full revolution.   

|The Moon presents the same side to Earth at all times.  That means that the rotation of the Earth offsets the separate effects of the revolution of the Moon. Physicists explain this phenomenon by [[tidal locking]]; tidal forces on Earth caused a bulge on the Moon, thereby creating a drag on the rotation of the Moon until its same face always presents to the Earth.  It was once believed that the planet [[Mercury]] had a similar locked rotation due to gravitational forces from the sun, such that the same side of Mercury always faces the sun. In fact, Mercury's tidal locking is incomplete; it does not always present the same face to the sun, but rather switches the side that it presents to the sun every full revolution.   

Current tidal forces exerted by the Earth on the Moon cannot account fully for its bulge or egg shape, though accounting for greater tidal forces in the past may explain this discrepancy.<ref>http://physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/AT308/HTML/AT30803.HTM</ref>

Current tidal forces exerted by the Earth on the Moon cannot account fully for its bulge or egg shape, though accounting for greater tidal forces in the past may explain this discrepancy.<ref>http://physics.fortlewis.edu/Astronomy/astronomy%20today/CHAISSON/AT308/HTML/AT30803.HTM</ref>