Space Telescope

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Introduction

Space Telescope, telescope or other astronomical detector mounted on an artificial satellite, a manned spacecraft, or another device outside Earth's atmosphere. The best-known and most famous space telescope is the Hubble Space Telescope (HST), in Earth orbit since 1990. Dozens of other space telescopes have been launched since the 1960s to study galaxies, stars, planets, and other objects and phenomena in space.

Observations made by telescopes in space have helped revolutionize our view of the universe, making major contributions to astronomy, physics and astrophysics, planetary sciences, and cosmology. With advancing technologies, the capabilities of new space telescopes continue to improve. At the same time new ground-based telescopes also become more sensitive and more powerful, sometimes equaling or exceeding results from earlier space telescopes.

Space telescopes have several advantages over Earth-based telescopes. Telescopes in space offer a much clearer view of astronomical objects because their instruments are far above Earth’s turbulent, distorting atmosphere. Telescopes in space are free from light pollution, artificially generated light that makes it difficult to observe faint astronomical objects. Space telescopes also can cover the entire celestial sphere, whereas portions of the sky may not be accessible to stationary ground-based telescopes, depending on their location on Earth.

Space telescopes also are not limited to observing the narrow band of light that is visible to the eye. Instead they have access to the entire electromagnetic spectrum, including infrared light, ultraviolet light, X rays, and gamma rays. The atmosphere entirely blocks some portions of the spectrum from reaching the ground, so satellites that can detect radiation from those portions offer new windows onto the universe that carry a wealth of information about planets, stars, and galaxies, and also the processes that shape them. Phenomena such as active galaxies and black holes cannot be fully understood without comparing data from across the electromagnetic spectrum.

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Space telescopes range in complexity from small satellites, which often survey the entire sky, to larger “observatory-class” satellites, which can target particular objects. These larger satellites generally require more intensive control from scientists on the ground, who choose objects to be studied and help point the satellites in the correct direction.

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Early Space Telescopes

Nearly a century ago Russian theorist Konstantin Tsiolkovsky and German rocket scientist Hermann Oberth recognized the advantage of placing an astronomical telescope in space, where starlight would not be blurred by the turbulence of Earth’s atmosphere. But it was not until after World War II (1939-1945), when rocket boosters were developed capable of hurtling satellites into orbit, that the dream of space-based astronomy became reality.

The British Ariel program launched the first astronomical satellites. Ariel 1, launched in April 1962, studied the Sun’s ultraviolet and X-ray emissions. The next space telescopes were from the Orbiting Astronomical Observatory (OAO) program of the United States National Aeronautics and Space Administration (NASA). OAO 2, the first successful OAO, was launched in December 1968 and carried infrared, ultraviolet, X-ray, and gamma-ray detectors and telescopes. As the first of their kind, these satellites provided valuable background for later and more complex space telescopes.

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Types of Space Telescopes

The Hubble Space Telescope is a general-purpose observatory that can detect different types of electromagnetic radiation from infrared to ultraviolet. However, most space telescopes are designed to study a particular range of wavelengths on the electromagnetic spectrum. The major divisions of the spectrum from longest to shortest wavelength are: radio, microwave, infrared, visible light, ultraviolet radiation, X ray, and gamma ray. Radio waves easily penetrate Earth’s atmosphere, so radio telescopes can be ground-based.

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Microwave Space Telescopes

Space telescopes that detect microwaves are used to study the earliest stages of the universe after the big bang 13.7 billion years ago. See also Background Radiation; Big Bang Theory.

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