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The sides of the Moon
The gravitational force of the Moon causes the ocean [[tides]]; these tidal forces have other effects as well. These tidal forces have the effect of creating resistance which slows down the rotation of both objects. In the case of the Earth, the result is that the Earth's rotation slows on the order of one millisecond per century. In the case of the Moon, over time the Moon has entirely lost its rotation relative to the Earth. The Moon's rotation is now locked in to its period of revolution, and the same side of the Moon always faces the Earth.
The gravitational force of the Moon causes the ocean [[tides]]; these tidal forces have other effects as well. These tidal forces have the effect of creating resistance which slows down the rotation of both objects. In the case of the Earth, the result is that the Earth's rotation slows on the order of one millisecond per century. In the case of the Moon, over time the Moon has entirely lost its rotation relative to the Earth. The Moon's rotation is now locked in to its period of revolution, and the same side of the Moon always faces the Earth.
The phrase "''dark'' side of the Moon" is inaccurate, however, because the Moon does rotate relative to the Sun, with the same period as its period of revolution, once every 29 days. Our view of the Moon from the Earth always shows the same side of the Moon, with the same markings and features. When the Moon is full, the entire side that faces us is experiencing lunar "day" and is lit by the Sun. Two weeks later, when the Moon is new, the side that faces us is experiencing solar "night" and is unlit (and virtually invisible).
==Unusual characteristics of the Moon==
==Unusual characteristics of the Moon==