fr en es pt
Contact the author rss astronoo

The origins of the Moon

The formation of the Moon

 Automatic translation  Automatic translation Updated June 01, 2013

There are over 150 moons in our solar system but the Earth has not one, it is what the Romans called "luna", it is remarkable for its size, it is only 4 times smaller than Earth. The Earth is the only one that has this configuration, the other planets have moons that very small compared to it. The Moon has no atmosphere at all and therefore no air molecule to color the sky is still black. The temperature ranges from -150 ° C when night falls to +132 ° C at noon.
From 4.2 billion years, meteorites have dug many craters, some of them are 1200 km in diameter.
The dark areas are called "husband" from the Latin word "sea". The lunar surface is static, there is no plate tectonics.
How to explain the formation of the Moon?
The imposing Moon impels us to ask about its origin since time immemorial. In 455 BC, the Greek philosopher Anaxagoras has theorized, the Moon is a rock that is detached from the earth, his contemporaries believed that the moon was a god.

 Crescent Moon

Image: Moonlight, taken in Caen - France, during the summer of 2009. Credit: Jean-Louis Lerossignol

MoonEarth's Moon
Diameter3 474,6 km
Mass7,34×1022 kg
Gravity 1,62 m/s²
Age4,2 billion years
Average temperature-77°C (+123°C-233°C)
Synodic period The synodic period of a planet is the time taken for this planet to return to the same configuration-planet Earth-sun, that is to say at the same place in the sky from the Sun as seen from Earth. This period differs from the sidereal period of revolution of the planet because the Earth itself moves around the Sun. Accordingly, it is the apparent rotation period, the time between two conjunctions planet-Sun, as seen from Earth. 29 days 12 h
44 min 12,8 s
Sidereal periodThe period of revolution is the time taken for a star to complete its trajectory, or revolution, around another star. As a planet around the Sun or a satellite around a planet. The time required to accomplish this shift can be estimated by the return to the same position relative to a fixed star, or the same position relative to the equinoctial point. In this case it is called sidereal period of revolution. 27 days 7 h
43 min 11,5 s
Inclination to the ecliptic5,145° = 5°8'24"
Apogee405 500 km
Perigee363 300 km
Distance from the earth+3,8 cm/year

The giant impact theory


In 1609 Italian astronomer Galileo pointed his telescope toward the moon and discovered a new landscape, another world. It is no longer flat, we see its curvature and the shadows of craters. It was not until 1873 that the first theory on the origin of the Moon is exposed by the French Edward Roche. He says that the Earth and Moon formed simultaneously from the same materials, but this theory is problematic because the materials of the Moon have an iron content significantly less than the Earth.
It has no iron core but consists simply of rock.
At the end of the 19th century other theories are born. In 1878, George Darwin, son of Charles Darwin and tidal specialist, explains his theory of nuclear fission to explain the origin of the Moon. He calculates that the moon gradually moves away from Earth.
This feature has been proven that 95 years later when astronomers go to the moon and deposit small mirrors that will be used to calculate the exact distance of the Moon with a laser beam.
Every year the moon moves away from Earth by 3.8 cm. Darwin calculated that the Moon was very close to the Earth at its origin but can not prove that the 2 stars at a time have joined, the mathematics of the time did not allow Darwin to bring the two stars in contact. Darwin concluded that when Earth was molten, material is detached it eventually became our moon.
A new theory is proposed in 1909 by the American Thomas Jefferson Jackson See, he developed a different hypothesis, which is called the capture theory.


The Moon would be gone too close to Earth and was captured by Earth gravity.
He believed there was a resisting medium in space to capture this hypothesis.
The 3 theories gather huge inconsistencies.
The rocks brought back by American astronomers during their first trip to the Moon will enable the development of another theory.
The moon rocks show that they are similar to terrestrial rocks.
William K. Hartmann planetary scientist and painter, imagined that another planet could have come crashing to Earth. This is the giant impact theory.
In 1974 a new assumption widely shared by scientists, therefore, sees the day.
4 billion years earlier would be another planet collided with Earth, then melts, and debris would be amalgamated within a few hours to form the Moon. Within a day the Earth would have resumed its spherical shape.

Image: William K. Hartmann was born in Pennsylvania, is a leading planetary scientist, author and writer. It was the first to convince the scientific public that Earth had been struck by a planet (Thea), creating both the moon and Earth.

 William K. Hartmann is a noted planetary scientist

1997 © − Astronomy, Astrophysics, Evolution and Ecology.
"The data available on this site may be used provided that the source is duly acknowledged."