Moon - Misplaced Pages

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Revision as of 18:28, 25 October 2006 by 209.146.25.1 (talk)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff) This article is about Earth's moon. For moons in general, see natural satellite. For other uses, see Moon (disambiguation).

Impressionism= LAME |- | colspan="2" bgcolor="#000000" align="center" |

The Moon as seen by an observer from Earth

min	mean	max
40 K	250 K	396 K

|- ! bgcolor="#ffc0c0" colspan="2" | Bulk composition of the Moon's mantle and crust |- | colspan="2" | estimated, weight percent |- | Oxygen | 42.6 % |- | Magnesium | 20.8 % |- | Silicon | 20.5 % |- | Iron | 9.9 % |- | Calcium | 2.31 % |- | Aluminium | 2.04 % |- | Nickel | 0.472 % |- | Chromium | 0.314 % |- | Manganese | 0.131 % |- | Titanium | 0.122 % |- ! bgcolor="#ffc0c0" colspan="2" | Atmospheric characteristics |- ! align="left" | Atmospheric pressure | 3 × 10kPa |- | Helium | 25 % |- | Neon | 25 % |- | Hydrogen | 23 % |- | Argon | 20 % |- | Methane
Ammonia
Carbon dioxide | trace |}

The Moon is Earth's only natural satellite. It has no formal English name other than "the Moon", although it is occasionally called Luna (Latin for moon), or Selene (Greek for moon), to distinguish it from the generic term "moon" (referring to any of the various natural satellites of other planets). Its symbol is a crescent. The related adjective for the Moon is lunar (again from the Latin root), but this is not found in combination, the combining forms seleno-/-selene (again from the Greek) and -cynthion (from the Lunar deity Cynthia) being used in terms relating to the Moon in various other contexts (e.g. aposelene, selenocentric, pericynthion, etc.).

The average distance from the Moon to the Earth is 384,401 kilometres (238,857 mi). The Moon's diameter is 3,476 kilometres (2,160 mi). Reflected sunlight from the Moon's surface reaches Earth in approximately 1.3 seconds (at the speed of light). The Moon is the Solar System's fifth largest moon, both by diameter and mass, ranking behind Ganymede, Titan, Callisto, and Io.

The first man-made object to impact the lunar surface was Luna 2 in 1959; the first photographs of the normally occluded far side of the Moon were made by Luna 3 in the same year. The first spacecraft to perform a successful lunar soft landing was Luna 9 in 1966. The first manned mission to orbit the Moon was Apollo 8, and the first people to land on the Moon came aboard Apollo 11 in 1969. It is the only celestial body other than the Earth upon which humans have set foot.

The two sides of the Moon

The Moon is in synchronous rotation, meaning that it keeps nearly the same face turned toward Earth at all times (there is a small variation, called libration). The side of the Moon that faces Earth is called the near side, and the opposite side is called the far side. The far side is also sometimes called the dark side, which means unknown and hidden, and not lacking light as might seem to be implied by the name; in fact, the far side receives (on average) slightly more sunlight than the near side due to lunar eclipse. Spacecraft are cut off from direct radio communication with Earth when on the far side of the Moon due to line-of-sight propagation. One distinguishing feature of the far side is its almost complete lack of maria (singular: mare), which are the dark albedo features.

90° W	Near side


90° E	Far side

Orbit and relationship to Earth

A scale model of Earth and the Moon

Main articles: The Moon's orbit and Earth and Moon

The Moon makes a complete orbit about the Earth approximately once every 27.3 days. It is at present in its {{moon

Onasch, Bernd (2006). "Moon". Retrieved 2006-03-20.
"Moon Fact Sheet". NSSDC. Retrieved 2006-03-20.