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The Moon is the Earth's only natural satellite. According to the systematic designation of satellites, the Moon is called Earth I; However in practice this form is not used. It is the fifth largest satellite in the Solar System, with a diameter of 3,474 km. The average distance between the Earth and the Moon is 384,467 km.
The Moon is the first and only non-terrestrial object visited by Man. The first to walk was astronaut Neil Armstrong on July 21, 1969. After him, eleven other men traveled to the Moon, all members of the Apollo program.
The length of the major axis between the Moon and the Earth is 384 399 km. The average diameter of the Moon is 3,474 km. The Earth's power on the Moon is about 1.95 × 1020 newtons.
Gravitational Influence on Earth
Among the most famous influences, from the most real to the most romantic, are:
•The tide: the Moon's revolutionary movement around the Earth induces a differential gravitational effect (in relation to the gravitational effect of Moon-Earth, seen from the center of the Earth) on the waters that make up the oceans and the seas, causing A local rise in water level at the Earth's surface, approximately in the Earth-Moon direction, and in the opposite direction. This differential effect is greater than that due to the Sun, even if on Earth the gravitational field of the Sun is greater than that of the Moon. The tidal wave is lagging behind the motion of the Moon due to the deformability of the water; A slow slowing down of the Earth's rotating motion follows, and a very slow departure from the Moon.
•Seismic activity: the magma of the mantle, present under the solid earth's crust, also undergoes its viscous state of motion, corresponding to the passage of the satellite. For some, fragmentation of the crust would be a consequence of the presence of the Moon. It is important to realize that this is plausible only because the Moon was much closer to Earth at its origins. For the volcanologist Jacques-Marie Bardintzeff, "the Moon has a well-known tidal effect on Earth. But its influence is too weak to trigger an eruption. However, for an active volcano, the Moon can slightly modify its behavior. Very different is the case of Io, moon (satellite) of Jupiter. The enormous Jupiter causes fantastic eruptions on Io. "
•The climate: during the different phases of the moon, the tidal force attracts more or less the atmosphere and thus participates, to the height of a few percent, in the phenomena of overpressure and depression.
•The growth of animals: the nautilus possesses a spiral shell formed of rings. Each day it forms an additional ring. At the end of a month a new internal partition is formed. If fossil shells are observed, the frequency of the internal partitions increases in proportion to their age. This is an indirect and independent confirmation of the lengthening of the month due to the progressive increase of the Earth-Moon distance. However, this hypothesis is increasingly contested.
•The obliquity of the earth: the obliquity of the Earth varies between 21 and 24 ° approximately with respect to the plane of the ecliptic. Mars, who has no comparable natural satellite, ranges from 20 ° to 60 °. Scientists therefore believe that the Moon stabilizes the Earth in its movement as if it were a counterweight - simply because the moment of inertia of the Earth-Moon system is much greater than that of the Earth alone.
•For a long time, the calendars indicate the phases of the Moon, especially for rural activities (night visibility) or fishing (tides).