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Man-made structures visible from earth orbit without magnification (by mechanical aids such as a camera or binoculars) include highways, dams, and cities.〔(Urban Legends.com website ). Accessed May 12, 2010.〕〔Cecil Adams, "Is the Great wall of China the only manmade object you can see from space?", ''The Straight Dope'', found at (The Straight Dope website ). Accessed May 12, 2010.〕〔Snopes, "Great wall from space", last updated 21 July 2007, found at (Snopes.com archives ). Accessed May 12, 2010.〕 The most commonly cited example, the Great Wall of China, is barely visible from Low Earth Orbit, and even then only under perfect conditions, but not from the moon.〔〔"the wall is only visible from low orbit under a specific set of weather and lighting conditions. And many other structures that are less spectacular from an earthly vantage point—desert roads, for example—appear more prominent from an orbital perspective." The Afsluitdijk in The Netherlands can also be seen from outer space''Scientific American'' found at (Is China's Great Wall Visible from Space? at Scientific American website ).〕 The Single largest man made structure, stretching over 170,000 km2, is Alberta's tailing ponds as a result of the Athabasca Oil Sands development. Part of the problem in authoritatively answering questions about visibility from space is that such questions are often very vaguely put: Askers frequently do not precisely define how far above sea level their hypothetical or actual observer in space is located. When just speaking of "space", an asker might mean anywhere from the edge of space (Kármán line) at an altitude of to Low Earth Orbit (160–2,000 km) to Apollo 12's orbit at to the Moon, which orbits about away.〔 The Kármán line is accepted by the Fédération Aéronautique Internationale (FAI), which is an international standard setting and record-keeping body for aeronautics and astronautics, as the boundary between the Earth's atmosphere and outer space. However, a practical definition for the purpose of answering questions on what astronauts generally can see from space would reflect altitudes that manned spacecraft typically orbit the Earth at—often several hundreds of kilometres.〔 Because of the inverse square law, there are major differences in visibility from just above the Kármán line (100+km/62+miles) and e.g. the ISS orbit (~394 km/~245miles). ==Examples== From the US Space Shuttle (which typically orbited at around ), cities were easily distinguishable from surrounding countryside.〔 Using binoculars, its astronauts could even see roads, airports, dams, harbors, even large vehicles such as ships and planes.〔〔(Starry Skies website )〕 Cities are also visible from the higher orbit of the ISS. Metropolitan areas are readily visible at night, particularly in industrialized countries, due to a multitude of street lights and other light sources in urban areas (see light pollution). 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「Man-made structures visible from space」の詳細全文を読む スポンサード リンク
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