See The Moon (post 6)

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The Moon is Earth's only natural satellite and the fifth largest satellite in the Solar System. It is the second largest natural satellite in the Solar System relative to the size of its primary (after Charon, which orbits dwarf planet Pluto), a quarter the diameter of Earth and 1/81 its mass. The Moon is the second densest satellite after Io. It is in synchronous rotation with Earth, always showing the same face; the near side is marked with dark volcanic maria among the bright ancient crustal highlands and prominent impact craters. It is the brightest object in the sky after the Sun, although its surface is actually very dark, with a similar reflectance to 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, the calendar, art and mythology.