Man-made structures visible from earth orbit without mechanical aids (such as a camera or binoculars) include highways, dams, and cities.[1][2][3][4] The most commonly cited example, the Great Wall of China, is not visible from space.[2][4][5]
Part of the problem of discerning fact from urban legend is defining how far up is "space", which could be anywhere from 100 kilometers (62 miles) up (the edge of space), or 290 km (180 miles) up (from Apollo 12's orbital),[clarification needed] to the moon, which orbits about 381,415 km (237,000 miles) away.[4] A best estimated definition would be in the hundreds of kilometres into space.[4] Another definition is the Kármán line, which is at the altitude of 100 km (62 miles) above the Earth's sea level. That 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.[6]
Cities are easily distinguishable from surrounding countryside by both shuttle astronauts in an Earth orbit 135 miles (217 kilometers) high[1] as from space stations, which orbit much higher, circling the planet at c. 250 miles (400 kilometers). Using binoculars, the astronauts can see roads, airports, dams, harbors, and even large vehicles and ships.[3][7] At an orbit of 160 to 350 miles, many such objects are visible from the Space Station.[4]
The concept has entered popular culture as a meme ("Many are familiar with the claim...")[2] trivia questions,[3] metaphor, urban legend,[1][4] and proverb, that certain constructed objects or effects are so large as to be visible from outer space. For example, a giant beaver dam in Canada was described as "so large it is visible from outer space."[8] Field and Stream asked and answered, "How big? Big enough to be visible ... from outer space."[9]
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The Great Wall of China is, proverbially, the man-made object most often cited as being visible from outer space. Claims have also been made that it is visible from the Moon.
Snopes.com credits writer Richard Halliburton for popularizing the idea in his 1938 book, Second Book of marvels, the Orient.[4] It has been widely debunked,[4][1][2][3] but is still ingrained in popular culture.[10] The viewer would need visual acuity 17 times better than normal (20/20) to see the Wall from the Moon, and vision 8 times better than normal to see it from low earth orbit.[11]
"The naked eye can tell the difference between cities and countryside from space." [12]
The "People's House" in Bucharest, Romania is the second largest building in the world, after The Pentagon, and has been cited as being visible from space.[13]
oil slick as seen from space by NASA's Terra satellite on May 1, 2010.]]
Large-scale pollution is almost invariably described in terms of visibility from space. The BP Spill or Deepwater Horizon oil spill of April 20, 2010 was so described in news stories,[14] on scientific websites,[15][16] as well as jokes about the spill.[17] Algae blooms and sewage, which are indirectly created by man-made pollution, are visible, and have been photographed, from space.[18][19]
The meme, that some bigger man-made objects are visible from outer space, has gotten into popular culture, often in the form of jokes. Very large objects are so often described in terms of visibility from space as to be a well-worn cliche.
The meme is expressed often in the form of jokes. For example, Chuck Norris' roundhouse kick is allegedly so powerful, that it can be seen from outer space.[20] Another common joke meme is that some persons's ego is so large as to be visible tens of thousands of miles into space.[17] A humor column in The Times claimed, tongue in cheek, that Tesco supermarkets wanted to illuminate all of their stores so that they would be visible from space, "like the Great Wall of China."[10] A satire claimed, facetiously, that a hockey rink in Toronto would be so large as to be seen from space.[21] A common form of mother joke references the size of the debate opponent's overweight mother.
Often, some work of art or advertising may be described as so big as to be "visible from space".[22]
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