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The Moon

Diameter3476 km, 0.27 x Earth's
Mass0.012 ME
Volume0.02 VE
Mean Density3.34 g/cm3
Mean Distance from Earth384400 km = 0.0025 AU
Eccentricity of Orbit0.055
Inclination of Equator to Orbit6.68°
Inclination of Orbit to Ecliptic5.15°
Night: -233°C
Orbital Period27.322 days
Rotational Period27.322 days
Gravity1/6 (0.16) of Earth's
Escape Velocity2.27 km/s

Buzz Aldrin in the Command Module

The Moon is the only natural satellite of Earth and the only other body in the Solar System to have been visited by humans. Neil Armstrong Gene Cernan salutes the American flag and Buzz Aldrin (left) landed on the surface of the Moon on 20th July 1969. A total of twelve men walked on its surface, the last being Gene Cernan (right) on December 19th 1972.

The Moon has no magnetic field, but a faint signature in the rocks suggest that it may have had one billions of years ago, implying an iron-rich core. The interior is divided into three distinct regions, a possible molten core, a mantle and a crust. Craters on the Moon There is no evidence of plate tectonics, and all of the surface features were created by impacts. The Moon is heavily cratered, but also has large flat plains called “maria.” These are thought to be caused by huge lava flows filling up particularly large impact basins.

Rocks on the surface of the Moon The chemical composition of the lunar rocks is very similar to those on Earth, suggesting that they may have been formed from the same body. The latest research suggests that the Moon was formed when a huge rock, about the size of Mars, smashed into the young Earth, vapourising a large proportion of the planet. The material ejected went into orbit around the Earth and slowly condensed to form the Moon.

There is no life on the Moon, and up until a few years ago there was thought to be no water. However, NASA’s spacecraft Clementine and Lunar Prospector have found evidence that there may be ice in the permanently shadowed craters at the poles.

Earthrise, as seen by the Apollo 11 astronauts

Planets Introduction













Extra-Solar Planets

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Authors: Carolyn Brinkworth and Claire Thomas

Last updated: July 2001