Earth - Moon


Diameter 3,474.8 km
Mass 7.349×1022 kg
Semi-major axis 384,400 km
Orbital period 27 d 7 h 43.7 m
Main article: Moon

The Moon is a relatively large, terrestrial, planet-like satellite, with a diameter about one-quarter of the Earth's. It is the largest moon in the Solar System relative to the size of its planet, although Charon is larger relative to the dwarf planet Pluto. The natural satellites orbiting other planets are called "moons" after Earth's Moon.

The gravitational attraction between the Earth and Moon causes tides on Earth. The same effect on the Moon has led to its tidal locking: its rotation period is the same as the time it takes to orbit the Earth. As a result, it always presents the same face to the planet. As the Moon orbits Earth, different parts of its face are illuminated by the Sun, leading to the lunar phases; the dark part of the face is separated from the light part by the solar terminator.

Due to their tidal interaction, the Moon recedes from Earth at the rate of approximately 38 mm a year. Over millions of years, these tiny modifications—and the lengthening of Earth's day by about 23 µs a year—add up to significant changes. During the Devonian period, for example, (approximately 410 mya) there were 400 days in a year, with each day lasting 21.8 hours.

The Moon may have dramatically affected the development of life by moderating the planet's climate. Paleontological evidence and computer simulations show that Earth's axial tilt is stabilized by tidal interactions with the Moon. Some theorists believe that without this stabilization against the torques applied by the Sun and planets to the Earth's equatorial bulge, the rotational axis might be chaotically unstable, exhibiting chaotic changes over millions of years, as appears to be the case for Mars.

Viewed from Earth, the Moon is just far enough away to have very nearly the same apparent-sized disk as the Sun. The angular size (or solid angle) of these two bodies match because, although the Sun's diameter is about 400 times as large as the Moon's, it is also 400 times more distant. This allows total and annular solar eclipses to occur on Earth.

The most widely accepted theory of the Moon's origin, the giant impact theory, states that it formed from the collision of a Mars-size protoplanet called Theia with the early Earth. This hypothesis explains (among other things) the Moon's relative lack of iron and volatile elements, and the fact that its composition is nearly identical to that of the Earth's crust.

Earth has at least five co-orbital asteroids, including 3753 Cruithne and 2002 AA29. As of 2011, there are 931 operational, man-made satellites orbiting the Earth. On July 27, 2011, astronomers reported a trojan asteroid companion, 2010 TK7, librating around the leading Lagrange triangular point, L4, of Earth in Earth's orbit around the Sun.

Read more about this topic:  Earth

Other articles related to "moon":

Sin (mythology) - Name
... The technical term for the crescent moon could also refer to the deity, DU4.SAKAR ... The Semitic moon god Su'en/Sin is in origin a separate deity from Sumerian Nanna, but from the Akkadian Empire period the two undergo syncretization and are identified ... with Akkadian na-an-na-ru "illuminator, lamp", an epitheton of the moon god ...
What If The Moon Didn't Exist
... What if the Moon Didn’t Exist is a collection of speculative articles about different versions of Earth, published in book form in 1993 ... individual scenarios are Solon – Earth without a Moon Lunholm – Moon closer to Earth Petiel – Earth with less mass Urania – Earth’s axis tilted like that of Uranus Granstar – More massive sun Antar ...
John Young (astronaut)
... who became the ninth person to walk on the Moon as commander of the Apollo 16 mission in 1972 ... and in 1969 was the first person to orbit the moon alone during Apollo 10 ... is one of only three persons who twice journeyed to the Moon, and drove the Lunar Roving Vehicle on the Moon's surface ...
... (also Meztli, Metzi) was a god or goddess of the moon, the night, and farmers ... He/she was probably the same deity as Yohaulticetl and Coyolxauhqui and the male moon god Tecciztecatl like the latter, he/she feared the sun because he/she feared its fire ... himself to become the sun, and became the moon instead, his face darkened by a rabbit ...
Moon - In Culture
... Further information Moon in fiction, Lunar calendar, Metonic cycle, Lunar deity, Lunar effect, and Blue moon The Moon's regular phases make it a very convenient timepiece, and the periods ... years ago, are believed by some to mark the phases of the Moon ... The same Indo-European root as moon led, via Latin, to measure and menstrual, words which echo the Moon's importance to many ancient cultures in measuring time (see ...

Famous quotes containing the word moon:

    There are two kinds of adventurers: those who go truly hoping to find adventure and those who go secretly hoping they won’t.
    —William Least Heat Moon [William Trogdon] (b. 1939)

    Her image was my ensign: snows melted,
    Hedges sprouted, the moon tenderly shone,
    The owls trilled with tongues of nightingale.
    Robert Graves (1895–1985)

    The sea is calm to-night.
    The tide is full, the moon lies fair
    Upon the straits;—
    Matthew Arnold (1822–1888)