Man-made structures visible from earth orbit without mechanical aids (such as a camera or binoculars) include highways, dams, and cities. The most commonly cited example, the Great Wall of China is not the easiest one to see.
Part of the problem of discerning fact from urban legend is defining how far up is "space", which could be anywhere from 60 miles up (the edge of space), or 180 miles up (from Apollo 12's obital), to the moon, which orbits about 237,000 miles away. A best estimated definition would be in the hundreds of miles into space. Another definition is the Kármán line, which is at the altitude of 100 km (just over 60 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.
Cities are easily distinguishable from surrounding countryside by both shuttle astronauts in an Earth orbit 135 miles (217 kilometers) high. They are just as visible on the Space station, which is in a higher orbit, circling the planet at 250 miles (400 kilometers). Using binoculars, the astronauts can see roads, airports, dams, harbors, and even large vehicles and ships.  At an orbit of 160 to 350 miles, many such objects are visible from the Space Station.
The concept has entered popular culture as a meme ("Many are familiar with the claim...") trivia questions, metaphor, urban legend, 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." Field and Stream asked and answered, "How big? Big enough to be visible ... from outer space."
Major man-made objectsEdit
"The naked eye can tell the difference between cities and countryside from space." 
The Great Wall of ChinaEdit
The Great Wall of China is, proverbially, the man-made object most often cited as being visible from outer space.
Snopes.com credits writer Richard Halliburton for popularizing the idea in his 1938 book, Second Book of marvels, the Orient. It has been widely debunked, but is still ingrained in popular culture.
Other buildings and constructed objectsEdit
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, as well as jokes about the spill. Algae blooms and sewage, which are indirectly created by man-made pollution, are visible, and have been photographed, from space.
In popular cultureEdit
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. Field and Stream referenced "dam big" jokes about the giant Alberta beaver dam. Another common joke meme is that some persons's ego is so large as to be visible tens of thousands of miles into space. 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." An satire claimed, facetiously, that a hockey rink in Toronto would be so large as to be seen from space. 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".
- ↑ 1.0 1.1 1.2 1.3 Urban Legends.com website. Accessed May 12, 2010.
- ↑ 2.0 2.1 2.2 2.3 "Can you see the Great Wall of China from the moon or outer space?", Answers.com, found at Answers.com. Accessed May 12, 2010.
- ↑ 3.0 3.1 3.2 3.3 Cecil Adams, Is the Great wall of China the only manmade object byou can see from space?", The Straight Dope, found at The Straight Dope website. Accessed May 12, 2010.
- ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 Snopes, "Great wall from space", last updated 21 July 2007, found at Snopes.com archives. Accessed May 12, 2010.
- ↑ "... 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." Scientific American found at Is China's Great Wall Visible from Space? at Scientific American website.
- ↑ "The 100 km Boundary for Astronautics" (DOC). Fédération Aéronautique Internationale Press Release. 2004-06-24. http://www.fai.org/press_releases/2004/documents/12-04_100km_astronautics.doc. Retrieved 2006-10-30.
- ↑ Starry Skies website
- ↑ 8.0 8.1 Michel Comte and Jacques Lemieu, "World's biggest beaver dam dsicovered in northern Canada," AFP, May 5, 2010, found at Yahoo News. Accessed May 12, 2010.
- ↑ 9.0 9.1 9.2 Field notes, "Giant Alberta Beaver Dam Is Visible from Space," found at Field and Stream website. Accessed May 12, 2010.
- ↑ 
- ↑ 11.0 11.1 "Metro Tescos", The Times (London), April 26, 2010. Found at The Times website. Accessed May 12, 2010.
- ↑ "Letter from Bucharest," The New Presence, vol, 1, no. 1, p. 47 (2004); abstract found at CEEOOL.com website. Accessed May 12, 2010.
- ↑ Tom Fletcher, BC Local news, May 4, 2010, found at BC Local News website. Accessed May 12, 2010.
- ↑ 14.0 14.1 "Which is more visible from outer space, the BP spill, or Obama's massive ego?", found at Yahoo Answers. Accessed May 12, 2010.
- ↑ "Satellite Images of Marine Phytoplankton Blooms," found at Geology.com. Accessed May 12, 2010.
- ↑ "Gaza sewage flood visible from outer space," Ma'an News Agency, found at Ma'an News site. Accessed May 12, 2010.
- ↑ GTA Forums Accessed May 12, 2010.
- ↑ Mark Schatzker, "The Lower Don lands will have the only hockey arena visible from space," Globe and Mail, May 7, 2010, found at The Globe and Mail website. Accessed May 12, 2010.
- ↑ Erica Pearson, "Molly Dilworth paints New York Rooftops so art is visible from space and on Google earth," Daily News, February 8, 2010, found at NY Daily News website. Accessed May 12, 2010.
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