The+Moon

The Moon completes a circuit around the Earth in a period whose mean or average duration is 27 days, 7 hours, 43.2 minutes. This is the Moon's sidereal period. Because of the motion of the Moon in common with the Earth around the Sun, the mean duration of the lunar month--the period from one New Moon to the next New Moon--is 29 days, 12 hours, 44.05 minutes. This is the Moon's synodical period. The mean distance of the Moon from the Earth is 238,857 mi. Because the orbit of the Moon about the Earth is not circular but elliptical, however, the maximum distance from the Earth that the Moon may reach is 252,710 mi and the least distance is 221,463 mi. (All distances are from the center of one body to the center of the other.) The Moon's diameter is 2,160 mi. If we deduct the radius of the Moon, 1,080 mi, and the radius of the Earth, 3,963 mi, from the minimum distance, or perigee, the figure for the nearest approach of the bodies' surfaces comes to 216,420 mi. The Moon rotates on its axis in a period of time that is exactly equal to its sidereal revolution about the Earth: 27.321666 days. Thus the backside or farside of the Moon always faces away from the Earth. This does not mean that the backside is always dark, since the Sun is the main source of light in the Solar System. The farside of the Moon gets just as much direct Sunlight as the nearside. At New Moon phase, the farside of the Moon is fully lit. In 1997, there is no Last Quarter Moon in February.