The Moon (Latin: luna) is the only natural satellite of the Earth, and the fifth largest satellite in the Solar System. It is the largest natural satellite of a planet in the Solar System relative to the size of its primary, having 27% the diameter and 60% the density of Earth, resulting in 1⁄81 its mass. The Moon is the second densest satellite after Io, a satellite of Jupiter.
The Moon is in synchronous rotation with Earth, always showing the same face with its near side marked by dark volcanic maria that fill between the bright ancient crustal highlands and the prominent impact craters. It is the brightest object in the sky after the Sun, although its surface is actually very dark, with a reflectance similar to that of coal. Its prominence in the sky and its regular cycle of phases have, since ancient times, made the Moon an important cultural influence on language, calendars, art and mythology. The Moon's gravitational influence produces the ocean tides and the minute lengthening of the day. The Moon's current orbital distance, about thirty times the diameter of the Earth, causes it to appear almost the same size in the sky as the Sun, allowing it to cover the Sun nearly precisely in total solar eclipses. This matching of apparent visual size is a coincidence. Earlier in Earth's history, the Moon was closer to Earth, and had an apparent visual size greater than that of the Sun.
The Moon is thought to have formed nearly 4.5 billion years ago, not long after the Earth. Although there have been several hypotheses for its origin in the past, the current most widely accepted explanation is that the Moon formed from the debris left over after a giant impact between Earth and a Mars-sized body. The Moon is the only celestial body other than Earth on which humans have set foot. The Soviet Union's Luna programme was the first to reach the Moon with unmanned spacecraft in 1959; the United States' NASA Apollo program achieved the only manned missions to date, beginning with the first manned lunar orbiting mission by Apollo 8 in 1968, and six manned lunar landings between 1969 and 1972, with the first being Apollo 11. These missions returned over 380 kg of lunar rocks, which have been used to develop a geological understanding of the Moon's origins, the formation of its internal structure, and its subsequent history.
After the Apollo 17 mission in 1972, the Moon has been visited only by unmanned spacecraft, notably by the final Soviet Lunokhod rover. Since 2004, Japan, China, India, the United States, and the European Space Agency have each sent lunar orbiters. These spacecraft have contributed to confirming the discovery of lunar water ice in permanently shadowed craters at the poles and bound into the lunar regolith. Future manned missions to the Moon have been planned, including government as well as privately funded efforts. The Moon remains, under the Outer Space Treaty, free to all nations to explore for peaceful purposes.
Other articles related to "moon":
... What if the Moon Didn’t Exist is a collection of speculative articles about different versions of Earth, published in book form in 1993 ...
... 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 ... na-an-na-ru "illuminator, lamp", an epitheton of the moon god ...
... (also Meztli, Metzi) was a god or goddess of the moon, the night, and farmers ... 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 ... failed to sacrifice himself to become the sun, and became the moon instead, his face darkened by a rabbit ...
... engineer, who became the ninth person to walk on the Moon as commander of the Apollo 16 mission in 1972 ... flew on the first manned Gemini mission, and in 1969 was the first person to orbit the moon alone during Apollo 10 ... He is one of only three persons who twice journeyed to the Moon, and drove the Lunar Roving Vehicle on the Moon's surface ...
... 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 ... dating as far back as 20–30,000 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 Latin mensis and Ancient Greek μήνας (mēnas ...
Famous quotes containing the word moon:
“The sea is calm to-night.
The tide is full, the moon lies fair
Upon the straits;”
—Matthew Arnold (18221888)
“in the pleasure of that communion
I lose track,
the moon I watch goes down, the
tide swings you away before
I know Im
alone again long since,”
—Denise Levertov (b. 1923)
“Seen from the moon we are all the same size.”
—Multatuli [Eduard Douwer Dekker] (18201887)