ultraviolet astronomy, study of celestial objects by means of the ultraviolet radiation UV index predicts how long it would take a light-skinned American to get a sunburn if exposed, unprotected, to the noonday sun, given the geographical location and the local weather.
..... Click the link for more information. 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 ozone layer or ozonosphere, region of the stratosphere containing relatively high concentrations of ozone , located at altitudes of 12–30 mi (19–48 km) above the earth's surface.
..... Click the link for more information. , oxygen, and nitrogen makes UV radiation difficult to observe from ground-based telescopes, high-altitude balloons, sounding rockets, and orbiting observatories observatory, orbiting, research satellite designed to study solar radiation, electromagnetic radiation from distant stars, the earth's atmosphere , or the like.
..... Click the link for more information. 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 Orbiting 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
..... Click the link for more information. (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 Orbiting 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
..... Click the link for more information. (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 Halley's comet or Comet Halley (hăl`ē, hā`lē)
..... Click the link for more information. during its 1986 approach, provided data about the UV reflectivity of the major planets, and contributed to the understanding of quasars quasar (kwā`sär), one of a class of blue celestial objects having the appearance of stars when viewed through a telescope and
..... Click the link for more information. ; 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 Hubble 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.
..... Click the link for more information. .

ultraviolet astronomy

Study of astronomical objects and phenomena by observing the ultraviolet radiation (UV radiation) they emit. It has yielded much information about chemical abundances and processes in interstellar matter, the Sun, and other stellar objects, such as hot young stars and white dwarf stars. Ultraviolet astronomy became feasible once rockets could carry instruments above Earth's atmosphere, which absorbs most electromagnetic radiation of UV wavelengths. Since the early 1960s, a number of unmanned space observatories carrying UV telescopes, including the Hubble Space Telescope, have collected UV data on objects such as comets, quasars, nebulae, and distant star clusters. The Extreme Ultraviolet Explorer, launched in 1992, was the first orbiting observatory to map the sky in the shortest UV wavelengths, at the boundary with the X-ray region of the electromagnetic spectrum.