Man-made structures visible from space

Man-made structures visible from earth orbit without magnification (by mechanical aids such as a camera or binoculars) include highways, dams, and cities.[1][2][3] 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.[3][4]

Part of the problem in authoritatively answering questions about visibility from space is that such questions are often very vaguely framed: 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 100 kilometers (62 mi) to Low Earth Orbit (160–2,000 km) to Apollo 12's orbit at 290 km (180 mi) to the Moon, which orbits about 381,415 km (237,000 mi) away.[3] The Kármán line is accepted by the Fédération Aéronautique Internationale (FAI), an international standard setting and record-keeping body for aeronautics and astronautics, as the boundary between the Earth's atmosphere and outer space.[5] 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.[3] Because of the inverse square law, there are major differences in visibility from just above the Kármán line (100+km/62+miles) and the ISS orbit (~394 km/~245miles), for example.

Examples

From the US Space Shuttle (which typically orbited at around 135 miles or 217 kilometres), cities were easily distinguishable from surrounding countryside.[1] Using binoculars, its astronauts could even see roads, airports, dams, harbors, even large vehicles such as ships and planes.[2][6] 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).

The Greenhouses of Almería

Greenhouses in the province of Almeria, Andalucía, Spain

The greenhouse complex that covers almost 50,000 acres (200 km2) in the province of Almería, Andalucía, Spain [7] is visible from space.[8]

The Kennecott Copper Mine

The Kennecott Copper Mine is the largest copper mine in the world. It can be seen from space. It is 2.5 miles (4.0 km) across.

Misconceptions

The Great Wall of China

The claim that the Great Wall of China is visible from outer space has been debunked many times,[1][2][3] but is still ingrained in popular culture.[9] A viewer would need visual acuity 8 times better than normal to see it from low earth orbit.[10]

Different claims are made for the factoid that the Great Wall is visible from the Moon. William Stukeley mentioned this claim in his letter dated 1754.[11] Henry Norman made the claim in 1895 as if it were already well known.[12] The issue of "canals" on Mars was prominent in the late 19th century and may have led to the belief that long, thin objects were visible from space.[13] A viewer would need visual acuity 17,000 times better than normal to see the Great Wall from the Moon.[10]

Popular culture

Trivia questions[2] and urban legends[1][3] often cite that certain constructed objects or effects are so large they are visible from outer space. For example, a giant beaver dam in Canada was described as "so large it is visible from outer space."[14] Field and Stream asked and answered, "How big? Big enough to be visible ... from outer space."[15]

Notes

  1. 1 2 3 4 Urban Legends.com website. Accessed May 12, 2010.
  2. 1 2 3 4 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.
  3. 1 2 3 4 5 6 Snopes, "Great wall from space", last updated 21 July 2007, found at Snopes.com archives. Accessed May 12, 2010.
  4. ↑ "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 spaceScientific American found at Is China's Great Wall Visible from Space? at Scientific American website.
  5. ↑ [http://www.fai.org/press_releases/2004/documents/12-04_100 km_astronautics.doc "The 100 km Boundary for Astronautics"] (DOC). Fédération Aéronautique Internationale Press Release. 2004-06-24. Retrieved 2006-10-30.
  6. ↑ Starry Skies website
  7. ↑ http://geographyfieldwork.com/AlmeriaClimateChange.htm
  8. ↑ http://www.popularmechanics.com/home/improvement/lawn-garden/worlds-18-strangest-gardens-greenhouses-of-almeria#slide-5
  9. ↑ "Metro Tesco", The Times (London), April 26, 2010. Found at The Times website. Accessed May 12, 2010.
  10. 1 2 Norberto López-Gil. "Is it Really Possible to See the Great Wall of China from Space with a Naked Eye?" (PDF). Journal of Optometry 1 (1): 3–4. doi:10.3921/joptom.2008.3.
  11. ↑ The Family Memoirs of the Rev. William Stunky (1887) Vol. 3, p. 142. (1754) "Chinese wall, which makes a considerable figure upon the terrestrial globe, and may be discerned at the moon."
  12. ↑ Norman, Henry, The Peoples and Politics of the Far East, p. 215. (1895) "Besides its age it enjoys the reputation of being the only work of human hands on the globe visible from the moon."
  13. ↑ "How is Great Wall of China from Space?"
  14. ↑ Michel Comte and Jacques Lemieu, "World's biggest beaver dam discovered in northern Canada," AFP, May 5, 2010, found at Yahoo News. Accessed May 12, 2010.
  15. ↑ Field notes, "Giant Alberta Beaver Dam Is Visible from Space," found at Field and Stream website. Accessed May 12, 2010.

External links

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