The Moon is thought to have formed about 4.51 billion years ago, not long after Earth. The most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and aMars-sized body called Theia.
The Moon is in synchronous rotation with Earth, always showing the same face, with itsnear side marked by dark volcanic maria that fill the spaces between the bright ancient crustal highlands and the prominent impact craters. As seen from the Earth, it is the second-brightest regularly visible celestial object in Earth's sky, after the Sun. Its surface is actually dark, although compared to the night sky it appears very bright, with areflectance just slightly higher than that of worn asphalt. Its gravitational influence produces the ocean tides, body tides, and theslight lengthening of the day.
The Moon's current orbital distance is 384,400 km (238,900 mi),[10][11] or 1.28 light-seconds. This is about thirty times the diameter of Earth, with its apparent size in the sky almost the same as that of the Sun, resulting in the Moon covering the Sun nearly precisely in total solar eclipse. This matching of apparent visual size will not continue in the far future, because the Moon's distance from Earth is slowly increasing.
The Soviet Union's Luna programme was the first to reach the Moon with uncrewed spacecraft in 1959; the United States' NASAApollo program achieved the only crewed missions to date, beginning with the first crewed lunar orbiting mission by Apollo 8 in 1968, and six crewed lunar landings between 1969 and 1972, with the first being Apollo. These missions returned lunar rocks which have been used to develop a geologicalunderstanding of the Moon's origin, internal structure, and later history. Since the Apollo 17 mission in 1972, the Moon has been visited only by uncrewed spacecraft.
Earth is a good place to be
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