Moon

## The Moon ☽

The Moon is Earth's only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits.

## Description

The **Moon** (Latin name: Luna) is Earth's only natural satellite. It is fifth-largest and the second-densest (after Jupiter's satellite Io) natural satellite in the Solar System. The Moon is exceptionally large relative to Earth: a quarter its diameter and 1/81 its mass. It is the largest moon in the Solar System relative to the size of its planet (though Charon is larger relative to the dwarf planet Pluto, at 1/9 Pluto's mass). Earth and the Moon are nevertheless still considered a planet-satellite system, rather than a double planet, because their barycentre, the common centre of mass, is located 1700 km (about a quarter of Earth's radius) beneath Earth's surface.

## Formation

The Moon is thought to have formed approximately 4.5 billion years ago, not long after Earth. Although there have been several hypotheses for its origin in the past, the current most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body called Theia.

## Visibility from Earth

The Moon 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. It is the second-brightest regularly visible celestial object in Earth's sky (after the Sun), as measured by illuminance on Earth's surface. Although it can appear a very bright white, 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.

## Distance and apparent size

The Moon's gravitational influence produces the ocean tides and the slight lengthening of the day. The Moon's current orbital distance is about thirty times the diameter of Earth, causing it to have an apparent size in the sky almost the same as that of the Sun. This allows the Moon to cover the Sun nearly precisely in total solar eclipse. This matching of apparent visual size is a coincidence. The Moon's linear distance from Earth is currently increasing at a rate of 3.82 ± 0.07 centimetres per year, but this rate is not constant.

1. ↑ This article was adapted from Space Engine's ingame wiki.

Topographical map of the Moon's near sideTopographical map of the Moon's far side
## Images

View of the transition between the Moon's near side and far sideThe far sideMare Nectaris, Mare Serenitatis and Mare Humboldtianum and below them the isolated Mare CrisiumCrescent of the Moon's far sideAnother view of the far side crescent. Near the terminator the Apollo and Oppenheimer craters can be seenClose up of the Mare Fecunditatis and the Langrenus Crater. Below it is the Mare Crisium, enclosed by high mountain chainsAnother shot of the Mare CrisiumClose up of the transition between far and near sideClose-up of various craters on the far sideAnother close-up of various craters on the far side. Among them the biggest ones are the Rotschild crater on the left and the Rozhdestvensky crater near the middle..Close-up of the polar regionMare Serenitatis and Mare TranquillitatisMare Serenitatis and Mare ImbriumThe Copernicus and Kepler cratersThe Mare OrientaleThe Leibnitz and Von Karman craters