Moon

The Moon is the only natural satellite of the Earth and the fifth largest moon in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having 27% the diameter and 60% the density of Earth, resulting in ¹⁄₈₁ its mass. Among satellites with known densities, the Moon is the second densest, after Io, a satellite of Jupiter.

The Moon is in synchronous rotation with Earth, always showing the same face with its near sidemarked by dark volcanic maria that fill between the bright ancient crustal highlands and the prominentimpact craters. It is the brightest object in the sky after the Sun, although its surface is actually dark, with a reflectance just slightly higher than that of worn asphalt. 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 theminute 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. This matching of apparent visual size is a coincidence. The Moon's linear distance from the Earth is currently increasing at a rate of 3.82±0.07 cm per year, but this rate is not constant

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