Natural satellite orbiting the Earth / From Wikipedia, the free encyclopedia
Dear Wikiwand AI, let's keep it short by simply answering these key questions:
Can you list the top facts and stats about Moon?
Summarize this article for a 10 years old
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet,[lower-alpha 6] with a diameter about one-quarter that of Earth (comparable to the width of Australia). The Moon is a planetary-mass object with a differentiated rocky body, making it a satellite planet under the geophysical definitions of the term and larger than all known dwarf planets of the Solar System. It lacks any significant atmosphere, hydrosphere, or magnetic field. Its surface gravity is about one-sixth of Earth's at 0.1654 g, with Jupiter's moon Io being the only satellite in the Solar System known to have a higher surface gravity and density.
|384399 km (1.28 ls, 0.00257 AU)|
(29 d 12 h 44 min 2.9 s)
Average orbital speed
|Inclination||5.145° to the ecliptic[lower-alpha 1]|
Regressing by one revolution in 18.61 years
Progressing by one
revolution in 8.85 years
|Satellite of||Earth[lower-alpha 2]|
|1737.4 km |
(0.2727 of Earth's)
|1738.1 km |
(0.2725 of Earth's)
|1736.0 km |
(0.2731 of Earth's)
|Circumference||10921 km (equatorial)|
|3.793×107 km2 |
(0.074 of Earth's)
|Volume||2.1958×1010 km3 |
(0.02 of Earth's)
|Mass||7.342×1022 kg |
(0.0123 of Earth's)
0.606 × Earth
|1.622 m/s2 (0.1654 g; 5.318 ft/s2)|
(8600 km/h; 5300 mph)
(29 d 12 h 44 min 2.9 s; synodic; solar day) (spin-orbit locked)
|27.321661 d (spin-orbit locked)|
Equatorial rotation velocity
North pole right ascension
North pole declination
|Surface absorbed dose rate||13.2 μGy/h (during lunar daytime)|
|Surface equivalent dose rate||57.0 μSv/h (during lunar daytime)|
|29.3 to 34.1 arcminutes[lower-alpha 4]|
|Composition by volume|
The Moon orbits Earth at an average distance of 384,400 km (238,900 mi), or about 30 times Earth's diameter. Its gravitational influence is the main driver of Earth's tides and very slowly lengthens Earth's day. The Moon's orbit around Earth has a sidereal period of 27.3 days. During each synodic period of 29.5 days, the amount of its Earth-facing surface illuminated by the Sun varies from none up to nearly 100%, resulting in lunar phases that form the basis for the months of a lunar calendar. The Moon is tidally locked to Earth, which means that the length of a full rotation of the Moon on its own axis causes its same side (the near side) to always face Earth, and the somewhat longer lunar day is the same as the synodic period. However, 59% of the total lunar surface can be seen from Earth through cyclical shifts in perspective known as libration.
The most widely accepted origin explanation posits that the Moon formed 4.51 billion years ago, not long after Earth, out of the debris from a giant impact between the planet and a hypothesized Mars-sized body called Theia. It then receded to a wider orbit because of tidal interaction with the Earth. The near side of the Moon is marked by dark volcanic maria ("seas"), which fill the spaces between bright ancient crustal highlands and prominent impact craters. Most of the large impact basins and mare surfaces were in place by the end of the Imbrian period, some three billion years ago. The lunar surface is fairly non-reflective, with the reflectance of lunar soil being comparable to that of asphalt. However, due to its large angular diameter, the full moon is the brightest celestial object in the night sky. The Moon's apparent size is nearly the same as that of the Sun, allowing it to cover the Sun almost completely during a total solar eclipse.
Both the Moon's prominence in Earth's sky and its regular cycle of phases have provided cultural references and influences for human societies throughout history. Such influences can be found in language, calendar systems, art, and mythology. The first artificial object to reach the Moon was the Soviet Union's uncrewed Luna 2 spacecraft in 1959; this was followed by the first successful soft landing by Luna 9 in 1966. The only human lunar missions to date have been those of the United States' Apollo program, which landed twelve men on the surface between 1969 and 1972. These and later uncrewed missions returned lunar rocks that have been used to develop a detailed geological understanding of the Moon's origins, internal structure, and subsequent history. The Moon is the only celestial body visited by humans.