Extreme Ultraviolet Explorer


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ultraviolet astronomy

ultraviolet 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 of interstellar gas and dust, and the temperature and composition of hot young stars. UV observations can also provide essential information about the evolution of galaxies. Because atmospheric interference from the ozone layer, oxygen, and nitrogen makes UV radiation difficult to observe from ground-based telescopes, high-altitude balloons, sounding rockets, and orbiting observatories are employed.

Although attempts to study the sun's UV spectrum from balloons were made during the 1920s, it was not until 1946 that rocket-borne instruments made this possible. Only limited additional progress was made until 1962, when the first Orbiting Solar Observatory (OSO) satellite was launched by the National Aeronautics and Space Administration (NASA). These returned thousands of UV spectra, including the first exteme-ultraviolet (wavelengths below 200 nanometers) observations of the solar corona. Through continuous monitoring of the sun over a 15-year period, this program enhanced our understanding of the solar atmosphere and of the 11-year sunspot cycle.

NASA's Orbiting Astronomical Observatory (OAO) satellites, the first of which was launched in 1966, returned UV data about stars and interstellar gas and dust and the first observations of the powerful UV radiation emitted by certain galaxies. Data from Copernicus (OAO-3), which was launched in 1972, led to the determination of the abundance of deuterium in interstellar matter; it also provided considerable information about the atmospheres of luminous hot stars. The Netherlands Astronomical Satellite (ANS) and the TD-1 satellite performed photometric and spectrophotometric surveys of stars in the UV wavelengths.

The International Ultraviolet Explorer (IUE)—a joint project of the United States, the European Space Agency, and Great Britain—was launched in 1978. In orbit for a decade, it monitored the UV spectrum of Halley's comet during its 1986 approach, provided data about the UV reflectivity of the major planets, and contributed to the understanding of quasars; its large telescope made possible the first UV observations of objects beyond the Milky Way, permitting the determination of temperature and structural changes of cool stars during their starspot cycles. The Extreme Ultraviolet Explorer (EUVE; 1992–2000) was the first orbiting observatory to focus on that part of the spectrum. In addition to data from these satellites, UV observations have also been made from two satellites launched in 1990 primarily for other purposes, the X-ray astronomy satellite ROSAT [ROentgen SATellite] and the Hubble Space Telescope.

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Extreme Ultraviolet Explorer

(EUVE) A NASA satellite launched June 1992 to carry out the first survey of the sky in the extreme ultraviolet (7–76 nm) region of the spectrum. Radiation at these wavelengths is totally screened out by the Earth's atmosphere, and so this mission was expected to be of groundbreaking significance. The 3.2-tonne satellite carried four photometric imaging systems and a three-channel EUV spectrometer. The imaging instruments were used to accomplish the sky survey. The spectrometers were used for the pointed spectroscopic programs, which collected data from over 350 unique astronomical targets. NASA authorized a Guest Observer Program of pointed spectroscopy that ended on Jan. 31, 2001, when the EUVE was shut down. The satellite fell out of orbit and broke up in the Earth's atmosphere at the end of Jan. 2002.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006
References in periodicals archive ?
Both the venerable International Ultraviolet Explorer satellite, now in its 17th year of operation, and the Extreme Ultraviolet Explorer craft, launched in 1992, will take spectra of the plumes of material carried aloft by the Jovian explosions.
Welsh of NASA headquarters and his colleagues have used ultraviolet data from two orbiting observatories, ROSAT and the Extreme Ultraviolet Explorer, to map the contours of a huge void in space that extends about 600 light-years across, well beyond the solar system.
Now, the Roentgen satellite (ROSAT) and the Extreme Ultraviolet Explorer (EUVE) spacecraft have provided new details of the sun's environment.
The Extreme Ultraviolet Explorer (EUVE), launched last June, detects this band of radiation, which can't penetrate Earth's atmosphere and is intermediate in energy between the near ultraviolet and X-rays (SN: 5/23/92, p.344).
Stuart Bowyer of the University of California, Berkeley, announced that another space-borne observatory, the recently launched Extreme Ultraviolet Explorer, detected a quasar-like object about 2 billion light-years from Earth.

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