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The Apache Point Observatory Lunar Laser-ranging Operation, or APOLLO,〔(【引用サイトリンク】title=The Apache Point Observatory Lunar Laser-ranging Operation )〕 is a project at the Apache Point Observatory in New Mexico. It is an extension and advancement of previous Lunar Laser Ranging Experiment, which uses retroreflectors on the Moon to track changes in lunar orbital distance and motion. Using telescopes on Earth, the reflectors on the Moon, and accurate timing of laser pulses, by the early 2000s scientists could measure and predict the orbit of the Moon to an accuracy of a few centimeters. This already impressive accuracy (the Moon is typically about 385,000 km away) provides the best known test of many aspects of our theories of gravity. APOLLO improves this even further, measuring the distance between the Moon to an accuracy of a few millimeters. Using this information, scientists will be able to further test various aspects of gravity: do the Earth and the Moon react the same to gravity despite their different compositions? Does the energy content of the Earth and the Moon react to gravity in the same way as Einstein predicts? In general, does Einstein's General Relativity correctly predict the motion of the Moon, or are new theories required? The APOLLO collaboration built their apparatus on the 3.5 meter telescope at Apache Point in southern New Mexico. By using a large telescope at a site with good atmospheric "seeing", the APOLLO collaboration gets much stronger reflections than any existing facilities. (Strong is a relative term here—APOLLO records approximately one returned laser photon per pulse, as opposed to the roughly 0.01 photon-per-pulse average experienced by previous LLR facilities.) The stronger return signal from APOLLO translates to much more accurate measurements. == History and motivation == High precision Lunar Laser Ranging (LLR) started soon after the Apollo 11 astronauts left the first retroreflector on the Moon.〔(【引用サイトリンク】title=History of Laser Ranging and MLRS )〕 Additional reflectors were left by the Apollo 14 and Apollo 15 astronauts, and two French-built reflector arrays were placed on the Moon by the Soviet Luna 17 (Lunokhod 1) and Luna 21 (Lunokhod 2) lunar rover missions. Over the years since, many groups and experiments have used this technique to study the behavior of the Earth-Moon system, investigating gravitational and other effects. For the first few years, the distance between the observatory and the reflectors could be measured to about 25 cm accuracy. Improved techniques and equipment lead to accuracies of 12–16 cm until about 1984. Then McDonald Observatory built a special purpose system (MLRS) just for ranging, and achieved roughly 3 cm accuracies mid-to-late 1980s. In the early 1990s a French LLR system at the Observatoire de la Côte d’Azur (OCA) started operation, with similar precision.〔 The McDonald and OCA stations are collecting data that is about as good as possible, given the number of photons they collect back from the reflectors. Although minor improvements are certainly possible, getting significantly better data requires a larger telescope and a better site. This is the basic goal of the APOLLO collaboration. The APOLLO laser has been operational since October 2005, and routinely accomplishes millimeter level range accuracy between the Earth and the Moon. 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「Apache Point Observatory Lunar Laser-ranging Operation」の詳細全文を読む スポンサード リンク
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