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In astronomy, a lunar distance (LD) is a measurement of the distance from the Earth to the Moon. The average distance from the center of the Earth to the center of the Moon is . One astronomical unit is about 389 LD. The actual distance varies over the course of the orbit of the moon, from at the perigee and at apogee, resulting in a differential range of . Millimeter-precision measurements of the lunar distance are made by measuring the time taken for light to travel between LIDAR stations on the Earth and retroreflectors placed on the Moon. Lunar laser ranging measurement data is available from the Paris Observatory Lunar Analysis Center,〔("LUNAR LASER RANGING OBSERVATIONS FROM 1969 TO MAY 2013" ) SYRTE Paris Observatory, retrieved 3 June 2014〕 and the active stations. The Moon is spiraling away from the Earth at an average rate of per year, as detected by the Lunar Laser Ranging Experiment.〔(Is the Moon moving away from the Earth? ) / Our Solar System, The Moon. Ask the Astronomer, Cornell University〕 The recession rate is considered anomalously high. By coincidence, the diameter of corner cubes in retroreflectors on the Moon is also .〔http://eclipse.gsfc.nasa.gov/SEhelp/ApolloLaser.html〕〔http://www.physics.ucsd.edu/~tmurphy/apollo/lrrr.html〕 The tidal dissipation rate has varied during the Earth's geological history.〔http://isotope.colorado.edu/~geol5700/Bills_1999.pdf - Lunar orbital evolution〕 The first person to measure the distance to the Moon was the 2nd-century-BC astronomer and geographer Hipparchus, who exploited the lunar parallax using simple trigonometry, measuring the distance as 400,000 kilometers. He was approximately off the actual distance, an error of about 6.8%. The NASA Near Earth Object Catalog includes the distances of asteroids and comets measured in Lunar Distances.〔(NEO Earth Close Approaches )〕 == See also == *Orbit of the Moon *Lunar Laser Ranging Experiment *Astronomical unit 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lunar distance (astronomy)」の詳細全文を読む スポンサード リンク
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