Artificial structures visible from space without magnification include highways, dams, and cities.

Cecil Adams Cecil Adams is the pseudonymous author of '' The Straight Dope'', a popular question and answer column published in '' The Chicago Reader'' from 2 February 1973 to 2018. The true identity of Adams, whether a single individual or a group of auth ...

, "Is the Great wall of China the only manmade object you can see from space?", ''The Straight Dope'', found a
The Straight Dope website
Accessed 12 May 2010.Snopes, "Great wall from space", last updated 21 July 2007, found a
Snopes.com archives
Accessed 12 May 2010. The

Great Wall of China The Great Wall of China (, literally "ten thousand ''li'' wall") is a series of fortifications that were built across the historical northern borders of ancient Chinese states and Imperial China as protection against various nomadic grou ...

, often cited as the only human-made structure visible from space, is not visible from

low Earth orbit A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, with an altitude never m ...

without magnification, and even then can be seen only under perfect conditions. On the other hand, the centimetre-band Spaceborne Imaging Radar of

STS-59 STS-59 was a Space Shuttle program mission that took place in 1994. The launch was chronicled by the 1994 Discovery Channel special about the Space Shuttle program. Crew Mission highlights 9 April ''Endeavour'' began its sixth mission on ...

and STS-68 was able to detect not only the Great Wall but also invisible buried segments of it.JPL, April 18, 1996, Space Radar Reveals Ancient Segments of China's Great Wall
/ref> Whether an object is visible depends significantly on the height above

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardise ...

from where it is observed. The

Kármán line The Kármán line (or von Kármán line ) is an attempt to define a boundary between Earth's atmosphere and outer space, and offers a specific definition set by the Fédération aéronautique internationale (FAI), an international record-keeping ...

, at , is accepted by the

World Air Sports Federation In its most general sense, the term "world" refers to the totality of entities, to the whole of reality or to everything that is. The nature of the world has been conceptualized differently in different fields. Some conceptions see the wor ...

, an international standard-setting and record-keeping body for

aeronautics Aeronautics is the science or art involved with the study, design, and manufacturing of air flight–capable machines, and the techniques of operating aircraft and rockets within the atmosphere. The British Royal Aeronautical Society identif ...

and

astronautics Astronautics (or cosmonautics) is the theory and practice of travel beyond Earth's atmosphere into outer space. Spaceflight is one of its main applications and space science its overarching field. The term ''astronautics'' (originally ''astrona ...

, as the boundary between the

Earth's atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...

and

outer space Outer space, commonly shortened to space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty—it is a near-perfect vacuum containing a low density of particles, pred ...

. However, astronauts typically orbit the Earth at several hundreds of kilometres; the ISS, for example, orbits at about above the Earth, and the Moon orbits at about away.

Examples

From US

Space Shuttles The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...

, which typically orbited at around , cities were easily distinguishable from surrounding countryside. Using binoculars, astronauts could even see roads, dams, harbors, even large vehicles such as ships and planes. 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 Light pollution is the presence of unwanted, inappropriate, or excessive use of artificial lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting, during the day or night. Light po ...

Cooling pond of Chernobyl

The long cooling pond of the

Chernobyl Nuclear Power Plant The Chernobyl Nuclear Power Plant (ChNPP; ; ), is a nuclear power plant undergoing decommissioning. ChNPP is located near the abandoned city of Pripyat in northern Ukraine northwest of the city of Chernobyl, from the Belarus–Ukraine bor ...

is visible from space. In April 1997 it was photographed from the '' Mir'' space station, which was in orbit somewhere between and .

The Greenhouses of Almería

The

greenhouse A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of transparent material, such as glass, in which plants requiring regulated climatic conditions are grown.These ...

complex that covers about in the

province of Almería Almería (, also , ) is a province of the autonomous community of Andalusia, Spain. It is bordered by the provinces of Granada, Murcia, and the Mediterranean Sea. Its capital is the homonymous city of Almería. Almería has an area of . With ...

Andalucía Andalusia (, ; es, Andalucía ) is the southernmost autonomous community in Peninsular Spain. It is the most populous and the second-largest autonomous community in the country. It is officially recognised as a "historical nationality". The t ...

Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = '' Plus ultra'' ( Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , ...

is visible from space. 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

The

Bingham Canyon Mine The Bingham Canyon Mine, more commonly known as Kennecott Copper Mine among locals, 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 large ...

, more commonly known as Kennecott Copper Mine, is an

open-pit mining Open-pit mining, also known as open-cast or open-cut mining and in larger contexts mega-mining, is a surface mining technique of extracting rock or minerals from the earth from an open-air pit, sometimes known as a borrow. This form of min ...

operation extracting a large

porphyry copper deposit Porphyry copper deposits are copper ore bodies that are formed from hydrothermal fluids that originate from a voluminous magma chamber several kilometers below the deposit itself. Predating or associated with those fluids are vertical dikes of ...

southwest of

Salt Lake City Salt Lake City (often shortened to Salt Lake and abbreviated as SLC) is the capital and most populous city of Utah, United States. It is the seat of Salt Lake County, the most populous county in Utah. With a population of 200,133 in 2020, th ...

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to its ...

, in the

Oquirrh Mountains The Oquirrh Mountains is a mountain range that runs north-south for approximately 30 miles (50 km) to form the west side of Utah's Salt Lake Valley, separating it from Tooele Valley. The range runs from northwestern Utah County–centra ...

. The mine is the largest human-made excavation in the world.

Misconceptions

The Great Wall of China

The claim that the

is the only man-made object visible from the Moon or outer space has been debunked many times, but remains a common misconception in popular culture."Metro Tesco", ''

The Times ''The Times'' is a British daily national newspaper based in London. It began in 1785 under the title ''The Daily Universal Register'', adopting its current name on 1 January 1788. ''The Times'' and its sister paper '' The Sunday Times'' ...

'' (Londund a
The Times website
According to astronauts Eugene Cernan and Ed Lu, the Great Wall is visible from the lower part of

, but only under very favorable conditions. Different claims were historically made for the

factoid A factoid is either an invented or assumed statement presented as a fact, ''or'' a true but brief or trivial item of news or information. The term was coined in 1973 by American writer Norman Mailer to mean a piece of information that becomes ac ...

that the Great Wall is visible from the Moon.

William Stukeley William Stukeley (7 November 1687 – 3 March 1765) was an English antiquarian, physician and Anglican clergyman. A significant influence on the later development of archaeology, he pioneered the scholarly investigation of the prehistor ...

mentioned this claim in his letter dated 1754, and Henry Norman made the same claim in 1895. 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. A viewer would need visual acuity 17 000 times better than the norm to see the Great Wall from the Moon.

Theoretical calculation of visibility from the ISS

The human

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...

has an angular resolution of approximately 280 microradians (μrad) (approx 0.016° or 1 minute of arc), and the ISS targets an altitude of 400 km. 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, or about 5,000 μrad, each letter would need to be about {{cvt, 2.016, km, mi, 1, adj=ri0 in size for clear legibility in good conditions.

Notes

External links

Gateway to Astronaut Photography of Earth
Urban legends Megastructures *