observatory, orbiting

observatory, orbiting,

research satellitesatellite, artificial,
object constructed by humans and placed in orbit around the earth or other celestial body (see also space probe). The satellite is lifted from the earth's surface by a rocket and, once placed in orbit, maintains its motion without further rocket propulsion.
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 designed to study solar radiation, electromagnetic radiationelectromagnetic radiation,
energy radiated in the form of a wave as a result of the motion of electric charges. A moving charge gives rise to a magnetic field, and if the motion is changing (accelerated), then the magnetic field varies and in turn produces an electric field.
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 from distant stars, the earth's atmosphereatmosphere
[Gr.,=sphere of air], the mixture of gases surrounding a celestial body with sufficient gravity to maintain it. Although some details about the atmospheres of other planets and satellites are known, only the earth's atmosphere has been well studied, the science of
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, or the like. Because the atmosphere and other aspects of the earth's environment interfere with astronomical observations from the ground, especially in the ultraviolet and infrared portions of the spectrum, the decades since the 1960s have seen increasing emphasis on space-based observatories.

The U.S. Orbiting Solar ObservatoryOrbiting Solar Observatory
(OSO), series of eight orbiting observatories (see observatory, orbiting) launched between 1962 and 1971 by the National Aeronautics and Space Administration (NASA) to study the sun in the ultraviolet and X-ray wavelengths filtered out by the earth's
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 (OSO) program, comprising eight satellites launched between 1962 and 1971, was one of the earliest series of orbiting observatories; it studied the sun's atmosphere and the sunspot cycle. Also beginning in 1962 and extending through 1979 were the launches of the six satellites in Great Britain's Ariel program, which concentrated on solar ultraviolet and X radiation. The Orbiting Geophysical ObservatoryOrbiting Geophysical Observatory
(OGO), series of six orbiting observatories (see observatory, orbiting) launched between 1964 and 1969 by the National Aeronautics and Space Administration (NASA) to study the earth's atmosphere, ionosphere, and magnetosphere and the solar wind.
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 (OGO) program consisted of six satellites, launched between 1964 and 1969, that provided data on the earth's atmosphere, ionosphereionosphere
, series of concentric ionized layers forming part of the upper atmosphere of the earth from around 30 to 50 mi (50 to 80 km) to 250 to 370 mi (400 to 600 km) where it merges with the magnetosphere, the region of the Van Allen radiation belts.
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, and magnetosphere and on the solar windsolar wind,
stream of ionized hydrogen—protons and electrons—with an 8% component of helium ions and trace amounts of heavier ions that radiates outward from the sun at high speeds.
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. The Orbiting Astronomical ObservatoryOrbiting Astronomical Observatory
(OAO), series of four orbiting observatories (see observatory, orbiting) launched between 1966 and 1972 by the National Aeronautics and Space Administration (NASA) to provide astronomical data in the ultraviolet and X-ray wavelengths filtered
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 (OAO) program comprised four satellites, launched between 1966 and 1972, that studied astronomical phenomena at ultraviolet and X-ray wavelengths inaccessible to earthbound equipment.

In the following years, a large number of satellites were launched to study solar and galactic radio waves, X rays, gamma rays, and ultraviolet rays. In addition to the United States a number of countries participated, among them the Netherlands with ANS-1 (1974–76), which studied soft and hard X radiation; India with Aryabhata (1975), which returned atmospheric data for only four days before being silenced by a power failure; Japan with Hakucho (1979–85) and Tenma (1981–84), both of which studied X radiation; and the European Space Agency (ESA) with Exosat (1983–86), an X-ray observatory. This period also saw the first cooperative efforts, such as the International Ultraviolet Explorer (IUE), a joint effort of the United States, ESA, and Great Britain (1978–96), which returned data on ultraviolet radiation for 18 years.

ROSAT [Roentgen Satellite] (1990–99), a joint German-U.S.-British project, studied both X-ray and ultraviolet wavelengths never before imaged from space. It detected a new class of bright stars that shine only in the ultraviolet part of the spectrum and X-ray emissions from comets. The Cosmic Background Explorer (1989–93) studied microwave background radiation that no star or other known object could emit—it is believed to have come from the creation of the universe (see cosmologycosmology,
area of science that aims at a comprehensive theory of the structure and evolution of the entire physical universe. Modern Cosmological Theories
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). The Infrared Space Observatory (ISO; 1995–98), launched by ESA, found water in the Orion nebula and in the atmospheres of the giant planets and Titan, found fluoride molecules in interstellar space, and studied the "cool" galaxies first seen by the Infrared Astronomy Satellite (IRAS) in 1983. Another European-built orbiting observatory, the Solar and Heliospheric Observatory (SOHO), was launched by NASA in 1995. After reaching a position about 950,000 mi (1.5 million km) from the earth, where the gravitational attraction of the earth and the sun are in balance (called a Lagrangian point), SOHO initiated a program of solar physics studies, such as the solar wind and solar plumes.

To fully explore the cosmos it is necessary to collect and analyze radiation emitted by phenomena throughout the entire electromagnetic spectrum. Toward that end, NASA proposed the concept of great observatories, a series of four orbiting observatories designed to conduct astronomical studies over many different wavelengths. An important aspect of the program was to overlap the operations phases of the missions to enable astronomers to make concurrent observations of an object at different spectral wavelengths. The first member of the program and the largest orbiting observatory is the Hubble Space TelescopeHubble Space Telescope
(HST), the first large optical orbiting observatory. Built from 1978 to 1990 at a cost of $1.5 billion, the HST (named for astronomer E. P. Hubble) was expected to provide the clearest view yet obtained of the universe from a position some 350 mi (560 km)
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 (HST), which was deployed by a space shuttlespace shuttle,
reusable U.S. space vehicle (1981–2011). Developed by the National Aeronautics and Space Administration (NASA) and officially known as the Space Transportation System (STS), it was the world's first reusable spacecraft that carried human beings into earth
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 in 1990 and repaired in orbit in 1993. Subsequent servicing missions added capabilities to the HST, which observes the universe at ultraviolet, visual, and near-infrared wavelengths. The second great observatory, the Compton Gamma-Ray Observatory, was launched and deployed by a shuttle in 1991; it collected data on gamma-ray bursts, which are some of the most violent physical processes in the universe. The third great observatory, the Chandra X-ray Observatory, formerly called the Advanced X-ray Astrophysics Facility, was deployed from a shuttle and boosted into a high earth orbit in 1999; it focuses on such objects as black holes, quasars, and high-temperature gases throughout the X-ray portion of the electromagnetic spectrum. The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility, was the fourth and final element in the great observatory program; launched in Aug., 2003, and operating (despite the loss of coolant and some instruments in 2009) until 2020, it filled an important gap in wavelength coverage not available from earthbound telescopes.

The CoRoT space telescope, launched in 2006 and operated by the French space agency in conjunction with ESA and other international partners, has searched for and discovered rocky exoplanets somewhat larger than the earth and studied stellar surface acoustical waves in an attempt to improve the understanding of the physics of stars. In 2009 ESA launched the Herschel Space Telescope, with a 138-in. (3.5-m) mirror. Positioned some 930,000 mi (1.5 million km) from earth on a mission that lasted into 2013, it observed wavelengths from the infrared to the submillimeter and studied the formation of galaxies in the early universe and the formation of stars as well as objects in the solar system. On the same Ariane rocket that carried Herschel, ESA also launched Planck, which observed (2009–2013) the cosmic microwave background radiation. Kepler, like CoRoT, was designed to search for rocky, earthlike exoplanets that might be habitable. Launched by NASA in 2009 and in operation into 2018, it used a sensitive photometer to monitor the stars in its field of view for the transits of planets. The data from Kepler also has been used by other astronomers to make discoveries concerning the stars. The Swiss-ESA CHEOPS, which was launched in 2019 and began observations in 2020, is designed to determine the size of exoplanets whose mass has been estimated, thus allowing for those exoplanets characterization to be determined further.

See also gamma-ray astronomygamma-ray astronomy,
study of astronomical objects by analysis of the most energetic electromagnetic radiation they emit. Gamma rays are shorter in wavelength and hence more energetic than X rays (see gamma radiation) but much harder to detect and to pinpoint.
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; infrared astronomyinfrared astronomy,
study of celestial objects by means of the infrared radiation they emit, in the wavelength range from about 1 micrometer to about 1 millimeter. All objects, from trees and buildings on the earth to distant galaxies, emit infrared (IR) radiation.
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; space probespace probe,
space vehicle carrying sophisticated instrumentation but no crew, designed to explore various aspects of the solar system (see space exploration). Unlike an artificial satellite, which is placed in more or less permanent orbit around the earth, a space probe is
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; ultraviolet astronomyultraviolet astronomy,
study of celestial objects by means of the ultraviolet radiation they emit, in the wavelength range from about 90 to about 350 nanometers. Ultraviolet (UV) line spectrum measurements are used to discern the chemical composition, densities, and temperatures
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; X-ray astronomyX-ray astronomy,
study of celestial objects by means of the X rays they emit, in the wavelength range from 0.01 to 10 nanometers. X-ray astronomy dates to 1949 with the discovery that the sun emits X rays.
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