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The Moon is an ellipsoidal astronomical body that orbits the Earth as its only natural satellite. It has a rocky silicate composition and is of planetary mass but has no significant atmosphere, hydrosphere or magnetic field. Its surface gravity is 0.1654 g, about one-sixth of Earth's. The Moon's average orbital distance from Earth is 384,402 km (238,856 mi)[13][14] or 1.28 light-seconds. Its gravitational influence produces Earth's tides and slightly lengthens Earth's day. The Moon's rotation on its own axis is tidally locked to Earth, so the same side always faces the planet. Changes in perspective when the Moon is viewed from Earth make 59% of the total lunar surface visible.[15] Because the Earth is rotating, the Moon's orbital period is defined in two different ways. From the Earth's perspective a full orbit by the Moon takes 27.3 days (the lunar sidereal period). From a fixed external perspective a single orbit takes 29.5 days (the synodic period). The lunar phases follow the synodic period and form the basis for the months of a lunar calendar—tidal locking makes the synodic period the same length as a lunar day. The near side of the Moon is marked by dark volcanic maria ("seas") filling the spaces between bright ancient crustal highlands and impact craters. The lunar surface is relatively non-reflective, with a reflectance just slightly brighter than that of worn asphalt. However, it reflects mainly direct sunlight, is contrasted by the relatively dark sky, and has a large apparent size viewed from Earth, making the Moon the brightest celestial object besides the Sun. Its apparent size in Earth's sky is almost the same as that of the Sun, allowing the Moon to cover the Sun nearly completely during a total solar eclipse. The mean diameter of the Moon is 3474.8 km, about one fourth of Earth's and comparable to the width of Australia.[16] It is considered a planetary-sized moon, is the fifth-largest planet-orbiting satellite in the Solar System, and is by far[17] the largest relative to the size of the planet it orbits.[f] It is larger than any dwarf planet and, among moons with a known density, has the second highest surface gravity and density in the Solar System after Jupiter's satellite Io. The Moon is thought to have formed about 4.51 billion years ago, not long after Earth. The most widely accepted explanation is that the Moon formed out of the debris from a giant impact between Earth and a hypothetical Mars-sized body called Theia. The first human-made object to reach the Moon was the Soviet Union's uncrewed Luna 2 spacecraft in September 1959, which was intentionally crashed onto the lunar surface. This was followed by the first successful soft landing on the Moon by Luna 9 in 1966. The only human lunar missions to date have been those of the United States' NASA Apollo program. The first human orbital mission was Apollo 8 in 1968 and there were six human landings between 1969 and 1972, beginning with Apollo 11 in July of 1969 and ending with the last human mission, Apollo 17 in 1972. These missions returned lunar rocks which have been used to develop a geological understanding of the Moon's origin, internal structure, and the Moon's later history. Both the Moon's natural prominence in the earthly sky and its regular cycle of phases as seen from Earth have provided cultural references and influences for human societies and cultures throughout history. Such cultural influences can be found in language, calendar systems, art, and mythology.

INTO JAPANESE

月は、唯一の自然衛星として地球を周回する楕円体の天体です。それは岩石のケイ酸塩組成を持ち、惑星の質量ですが、重要な大気、水圏、または磁場はありません。その表面重力は0.1654gで、地球の約6分の1です。月の地球からの平均軌道距離は384,402km（23

BACK INTO ENGLISH

The moon is an ellipsoidal celestial body that orbits the earth as the only natural satellite. It has a rock silicate composition and is the mass of the planet, but has no significant atmosphere, hydrosphere, or magnetic field. Its surface gravity is 0.1654g, which is about one sixth of that of the earth. The average orbital distance of the Moon from Earth is 384,402 km (23)

INTO JAPANESE

月は、唯一の自然衛星として地球を周回する楕円体の天体です。それは岩石ケイ酸塩組成を持ち、惑星の質量ですが、重要な大気、水圏、または磁場はありません。その表面重力は0.1654gで、地球の約6分の1です。月の平均軌道距離fr

BACK INTO ENGLISH

The moon is an ellipsoidal celestial body that orbits the earth as the only natural satellite. It has a rock silicate composition and is the mass of the planet, but there is no significant atmosphere, hydrosphere, or magnetic field. Its surface gravity is 0.1654g, which is about one sixth of that of the earth. Monthly average orbital distance fr

INTO JAPANESE

月は、唯一の自然衛星として地球を周回する楕円体の天体です。それは岩石ケイ酸塩組成を持ち、惑星の質量ですが、重要な大気、水圏、または磁場はありません。その表面重力は0.1654gで、地球の約6分の1です。月平均軌道距離fr

BACK INTO ENGLISH

The moon is an ellipsoidal celestial body that orbits the earth as the only natural satellite. It has a rock silicate composition and is the mass of the planet, but there is no significant atmosphere, hydrosphere, or magnetic field. Its surface gravity is 0.1654g, which is about one sixth of that of the earth. Monthly average orbital distance fr