Artificial structures visible from Earth orbit without magnification include highways, dams, and cities.[1][2][3] The Great Wall of China, often cited as the only human-made structure visible from space, is not visible from low Earth orbit without magnification, and even then can be seen only under perfect conditions.[3][4] On the other hand, the centimetre-band Spaceborne Imaging Radar of STS-59 and STS-68 was able to detect not only the Great Wall but also invisible buried segments of it.[5]

Whether an object is visible depends significantly on the height above sea level from where it is observed. The Kármán line, at 100 kilometres (62 mi), is accepted by the World Air Sports Federation, an international standard-setting and record-keeping body for aeronautics and astronautics, as the boundary between the Earth's atmosphere and outer space.[6] However, astronauts typically orbit the Earth at several hundreds of kilometres;[3] the ISS, for example, orbits at about 420 km (260 mi) above the Earth,[7] and the Moon orbits at about 380,000 km (240,000 mi) away.[3]

Examples

From US Space Shuttles, which typically orbited at around 135 mi (217 km), cities were easily distinguishable from surrounding countryside.[1] Using binoculars, astronauts could even see roads, dams, harbors, even large vehicles such as ships and planes.[2][8] At night, cities are also easily visible from the higher orbit of the ISS.

Metropolitan areas are clearly visible at night, particularly in industrialized countries, due to a multitude of street lights and other light sources in urban areas (see light pollution).

Cooling pond of Chernobyl

The region around the Chernobyl nuclear power plant, as seen from the Russian space station Mir
The region around the Chernobyl nuclear power plant, as seen from the Russian space station Mir

The 10-kilometre (6.2 mi) long cooling pond of the Chernobyl Nuclear Power Plant is visible from space. The photograph here was taken from the spaceship Mir, which was in orbit somewhere between 296 km (184 mi) and 421 km (262 mi), on 27 April 1997.

The Greenhouses of Almería

Greenhouses in the province of Almería, Andalucía, Spain

Main article: Intensive farming in Almería

The greenhouse complex that covers about 26 thousand hectares (64 thousand acres; 100 square miles) in the province of Almería, Andalucía, Spain[9] is visible from space.[10] It is sometimes referred to as the "Plastic sea" ("Mar de plástico" in Spanish) due to the high concentration of these greenhouse structures.

This area produces much of the fruit and vegetables that are sold in the rest of Spain and Europe. Apart from the area depicted in the photo, other zones of the province of Almería (and also the south of Spain) have large concentrations of white-plastic greenhouses too.

Bingham Canyon Mine

Bingham Canyon Mine near Salt Lake City, Utah from the International Space Station in 2007

The Bingham Canyon Mine, more commonly known as Kennecott Copper Mine,[11] is an open-pit mining operation extracting a large porphyry copper deposit southwest of Salt Lake City, Utah, in the Oquirrh Mountains. The mine is the largest man-made excavation in the world.[12]

Misconceptions

The Great Wall of China

The claim that the Great Wall of China is the only man-made object visible from the Moon or outer space has been debunked many times,[1][2][3] but remains a common misconception in popular culture.[13] According to astronauts Eugene Cernan and Ed Lu, the Great Wall is visible from the lower part of low Earth orbit, but only under very favorable conditions.[14]

Different claims were historically made for the factoid that the Great Wall is visible from the Moon. William Stukeley mentioned this claim in his letter dated 1754,[15] and Henry Norman made the same claim in 1895.[16] 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.[17] A viewer would need visual acuity 17 000 times better than normal to see the Great Wall from the Moon.[18]

Popular culture

Trivia questions[2] and urban legends[1][3] often claim 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."[19] Field and Stream wrote, "How big? Big enough to be visible ... from outer space."[20]

Theoretical calculation of visibility from the ISS

The human naked eye has an angular resolution of approximately 280 microradians[21] (μrad) (approx 0.016° or 1 minute of arc), and the ISS targets an altitude of 400 km.[22] Using basic trigonometric relations, this means that an astronaut on the ISS with 20/20 vision could potentially detect objects that are 112 m or greater in all dimensions. However, since this would be at the absolute limit of the resolution, objects on the order of 100 m would appear as unidentifiable specks, if not rendered invisible due to other factors, such as atmospheric conditions or poor contrast. For readability of text from the ISS, using the same trigonometric principles and a recommended character size of about 18 arcminutes,[23] or about 5,000 μrad, each letter would need to be about 2 km (1.3 mi) in size for clear legibility in good conditions.

See also

Notes

  1. ^ a b c d Emery, David. "What's Visible from Outer Space". About.com: Urban legends. Archived from the original on 2009-09-28. Retrieved 2010-05-12.((cite web)): CS1 maint: unfit URL (link)
  2. ^ a b c d 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. ^ a b c d e f 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 space Scientific American found at Is China's Great Wall Visible from Space? at Scientific American website.
  5. ^ JPL, April 18, 1996, Space Radar Reveals Ancient Segments of China's Great Wall
  6. ^ "The 100 km Boundary for Astronautics" (DOC). Fédération Aéronautique Internationale Press Release. 2004-06-24. Retrieved 2006-10-30.
  7. ^ Peat, Chris. "ISS – Orbit". Heavens-Above. Retrieved 7 January 2020.
  8. ^ Starry Skies website
  9. ^ "A Greenhouse Effect has cooled the climate of Almeria".
  10. ^ "The World's 18 Strangest Gardens". 11 August 2010.
  11. ^ Mcfarland, Sheena. "Kennecott Copper Mine recovering faster than predicted". The Salt Lake Tribune. The Salt Lake Tribune. Retrieved 28 April 2015.
  12. ^ Lee, Jasen (3 March 2016). "Kennecott laying off 200 workers". DeseretNews.com. Retrieved 2016-03-06.
  13. ^ "Metro Tesco", The Times (Londund at The Times website.
  14. ^ Scientific American, February 21, 2008. "Is China's Great Wall Visible from Space?"
  15. ^ The Family Memoirs of the Rev. William Stukeley (1887) Vol. 3, p. 142. (1754) "Chinese wall, which makes a considerable figure upon the terrestrial globe, and may be discerned at the moon."
  16. ^ 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."
  17. ^ "How is Great Wall of China from Space?"
  18. ^ Norberto López-Gil (2008). "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. PMC 3972694. Archived from the original (PDF) on 2009-10-07.
  19. ^ 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.
  20. ^ Field notes, "Giant Alberta Beaver Dam Is Visible from Space," found at Field and Stream website. Accessed May 12, 2010.
  21. ^ Miller, David; Schor, Paulo; Peter Magnante. "Optics of the Normal Eye", pg. 54 of Ophthalmology by Yanoff, Myron; Duker, Jay S. ISBN 978-0-323-04332-8
  22. ^ "NASA - Higher Altitude Improves Station's Fuel Economy". www.nasa.gov. Retrieved 2019-05-20.
  23. ^ "Text Size". www.hf.faa.gov. Archived from the original on 2018-11-27. Retrieved 2019-05-20.