The Moon is the only natural satellite of the Earth and the fifth largest satellite in the Solar System.
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It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having a quarter the diameter of Earth but only 1⁄81 its mass. The Moon is the second densest satellite after Io, a satellite of Jupiter. It is in synchronous rotation with Earth, always showing the same face with its near side marked by dark volcanic maria that fill between the bright ancient crustal highlands and the prominent impact craters. The Moon is the brightest object in the sky after the Sun, although its surface is actually very dark, with a reflectance similar to that of coal. Its prominence in the sky and its regular cycle of phases have, since ancient times, made the Moon an important cultural influence on language, calendars, art and mythology. The Moon’s gravitational influence produces the ocean tides and the minute lengthening of the day. The Moon’s current orbital distance, about thirty times the diameter of the Earth, causes it to appear almost the same size in the sky as the Sun, allowing it to cover the Sun nearly precisely in total solar eclipses. The Moon is the only celestial body other than Earth on which humans have set foot. The Soviet Union’s Luna programme was the first to reach the Moon with unmanned spacecraft in 1959; the United States’ NASA Apollo program achieved the only manned missions to date, beginning with the first manned lunar orbiting mission by Apollo 8 in 1968, and six manned lunar landings between 1969 and 1972, with the first being Apollo 11. These missions returned over 380 kg of lunar rocks, which have been used to develop a geological understanding of the Moon’s origins, the formation of its internal structure, and its subsequent history. It is thought to have formed some 4.5 billion years ago. One formation theory is a giant impact event involving Earth. The impact theory was called into question in 2012, after re-analysis of Apollo samples.
The Moon is approximately 384,400 km (239,000 miles) from the Earth.
The diameter of the Moon is 3479 kilometers (2162 miles). This is about 1/4 the diameter of the Earth (12,756 kilometers or 7,926 miles).
The mass of the Moon is 7.35*1022 kilograms, which is about 1/80 of the mass of the Earth.
The density of the Moon is 3340 kg/m3.
Density = mass divided by volume, d = m/V.
The volume of a sphere = 4/3 times pi times its radius cubed,
V = 4*π*r3/3.
The average temperature on the surface of the Moon during the day is 107°C.
During the night, the average temperature drops to −153°C.