Artificial structures visible from space 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 (62mi), 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 420km (260mi) above the Earth,[7] and the Moon orbits at about 380,000km (240,000mi) away.[3]
Examples
From US Space Shuttles, which typically orbited at around 135mi (217km), 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 in 1997
The 10-kilometre (6.2mi) long cooling pond of the Chernobyl Nuclear Power Plant is visible from space. In April 1997 it was photographed from the Mir space station, which was in orbit somewhere between 296km (184mi) and 421km (262mi).
The greenhouse complex that covers about 26thousand hectares (64thousand 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.
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 the norm to see the Great Wall from the Moon.[18]
Theoretical calculation of visibility from the ISS
The human naked eye has an angular resolution of approximately 280 microradians[19] (μrad) (approx 0.016° or 1 minute of arc), and the ISS targets an altitude of 400km.[20] Using basic trigonometric relations, this means that an astronaut on the ISS with 20/20 vision could potentially detect objects that are 112m or greater in all dimensions. However, since this would be at the absolute limit of the resolution, objects on the order of 100m 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,[21] or about 5,000 μrad, each letter would need to be about 2km (1.3mi) in size for clear legibility in good conditions.
1 2 3 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 12 May 2010.
1 2 3 4 5 Snopes, "Great wall from space", last updated 21 July 2007, found at Snopes.com archives. Accessed 12 May 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." 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.
↑ 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."
↑ 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."
↑ Miller, David; Schor, Paulo; Peter Magnante. "Optics of the Normal Eye", pg. 54 of Ophthalmology by Yanoff, Myron; Duker, Jay S. ISBN978-0-323-04332-8
An astronaut is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally reserved for professional space travelers, the term is sometimes applied to anyone who travels into space, including scientists, politicians, journalists, and tourists.
The International Space Station (ISS) is the largest modular space station in low Earth orbit. The project involves five space agencies: the United States' NASA, Russia's Roscosmos, Japan's JAXA, Europe's ESA, and Canada's CSA. The ownership and use of the space station is established by intergovernmental treaties and agreements. The station serves as a microgravity and space environment research laboratory in which scientific research is conducted in astrobiology, astronomy, meteorology, physics, and other fields. The ISS is suited for testing the spacecraft systems and equipment required for possible future long-duration missions to the Moon and Mars.
Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is currently carried out mainly by astronomers with telescopes, its physical exploration is conducted both by uncrewed robotic space probes and human spaceflight. Space exploration, like its classical form astronomy, is one of the main sources for space science.
Spaceflight is an application of astronautics to fly objects, usually spacecraft, into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such as satellites in orbit around Earth, but also includes space probes for flights beyond Earth orbit. Such spaceflight operate either by telerobotic or autonomous control. The more complex human spaceflight has been pursued soon after the first orbital satellites and has reached the Moon and permanent human presence in space around Earth, particularly with the use of space stations. Human spaceflight programs include the Soyuz, Shenzhou, the past Apollo Moon landing and the Space Shuttle programs. Other current spaceflight are conducted to the International Space Station and to China's Tiangong Space Station.
Outer space, commonly referred to simply as 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, predominantly a plasma of hydrogen and helium as well as electromagnetic radiation, magnetic fields, neutrinos, dust, and cosmic rays. The baseline temperature of outer space, as set by the background radiation from the Big Bang, is 2.7 kelvins.
Human spaceflight programs have been conducted, started, or planned by multiple countries and companies. The age of manned rocket flight was initiated by Fritz von Opel who piloted the world's first rocket-propelled flight on 30 September 1929. All space flights depend on rocket technology; von Opel was the co-designer and financier of the visionary project. Until the 21st century, human spaceflight programs were sponsored exclusively by governments, through either the military or civilian space agencies. With the launch of the privately funded SpaceShipOne in 2004, a new category of human spaceflight programs – commercial human spaceflight – arrived. By the end of 2022, three countries and one private company (SpaceX) had successfully launched humans to Earth orbit, and two private companies had launched humans on a suborbital trajectory.
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.
In astronomy, an extraterrestrial sky is a view of outer space from the surface of an astronomical body other than Earth.
The far side of the Moon is the lunar hemisphere that always faces away from Earth, opposite to the near side, because of synchronous rotation in the Moon's orbit. Compared to the near side, the far side's terrain is rugged, with a multitude of impact craters and relatively few flat and dark lunar maria ("seas"), giving it an appearance closer to other barren places in the Solar System such as Mercury and Callisto. It has one of the largest craters in the Solar System, the South Pole–Aitken basin. The hemisphere has sometimes been called the "dark side of the Moon", where "dark" means "unknown" instead of "lacking sunlight" – each side of the Moon experiences two weeks of sunlight while the opposite side experiences two weeks of night.
The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon.
The Great Wall of China 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 groups from the Eurasian Steppe. Several walls were built from as early as the 7th century BC, with selective stretches later joined by Qin Shi Huang (220–206 BC), the first emperor of China. Little of the Qin wall remains. Later on, many successive dynasties built and maintained multiple stretches of border walls. The best-known sections of the wall were built by the Ming dynasty (1368–1644).
The following outline is provided as an overview of and topical guide to space exploration.
The Moon is the largest natural satellite of and the closest major astronomical object to Earth. The Moon may be observed by using a variety of optical instruments, ranging from the naked eye to large telescopes. The Moon is the only celestial body upon which surface features can be discerned with the unaided eyes of most people.
Astrobotany is an applied sub-discipline of botany that is the study of plants in space environments. It is a branch of astrobiology and botany.
Space architecture is the theory and practice of designing and building inhabited environments in outer space. This mission statement for space architecture was developed at the World Space Congress in Houston in 2002 by members of the Technical Aerospace Architecture Subcommittee of the American Institute of Aeronautics and Astronautics (AIAA). The architectural approach to spacecraft design addresses the total built environment. It is mainly based on the field of engineering, but also involves diverse disciplines such as physiology, psychology, and sociology.
Space research is scientific study carried out in outer space, and by studying outer space. From the use of space technology to the observable universe, space research is a wide research field. Earth science, materials science, biology, medicine, and physics all apply to the space research environment. The term includes scientific payloads at any altitude from deep space to low Earth orbit, extended to include sounding rocket research in the upper atmosphere, and high-altitude balloons.
Comet Swift–Tuttle is a large periodic comet with a 1995 (osculating) orbital period of 133 years that is in a 1:11 orbital resonance with Jupiter. It fits the classical definition of a Halley-type comet, which has an orbital period between 20 and 200 years. The comet was independently discovered by Lewis Swift on July 16, 1862 and by Horace Parnell Tuttle on July 19, 1862.
The growth of plants in outer space has elicited much scientific interest. In the late 20th and early 21st century, plants were often taken into space in low Earth orbit to be grown in a weightless but pressurized controlled environment, sometimes called space gardens. In the context of human spaceflight, they can be consumed as food and/or provide a refreshing atmosphere. Plants can metabolize carbon dioxide in the air to produce valuable oxygen, and can help control cabin humidity. Growing plants in space may provide a psychological benefit to human spaceflight crews. Usually the plants were part of studies or technical development to further develop space gardens or conduct science experiments. To date plants taken into space have had mostly scientific interest, with only limited contributions to the functionality of the spacecraft, however the Apollo Moon tree project was more or less forestry inspired mission and the trees are part of a country's bicentennial celebration.
WT1190F was a small temporary satellite of Earth that impacted Earth on 13 November 2015 at 06:18:21.7 UTC. It is thought to have been space debris from the trans-lunar injection stage of the 1998 Lunar Prospector mission. It was first discovered on 18 February 2013 by the Catalina Sky Survey. It was then lost, and reacquired on 29 November 2013. It was again discovered on 3 October 2015 by astronomer Rose Garcia with the Catalina Sky Survey 60-inch telescope, and the object was soon identified to be the same as the two objects previously sighted by the team, who have been sharing their data through the International Astronomical Union's Minor Planet Center (MPC). An early orbit calculation showed that it was orbiting Earth in an extremely elliptical orbit, taking it from within the geosynchronous satellite ring to nearly twice the distance of the Moon. It was also probably the same object as 9U01FF6, another object on a similar orbit discovered on 26 October 2009.
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