The study of the Universe in the ultraviolet region of the electromagnetic spectrum, approximately 91.2–320 nm. These wavelengths are largely blocked by the Earth’s atmosphere, so observations became possible only with the use of rockets after World War II. Balloons were also used, but the altitude they could achieve allowed observations only in the near ultraviolet, longer than 200 nm.
The Orbiting Astronomical Observatory series of ultraviolet missions commenced in 1968. In 1972 OAO-3, also known as Copernicus, revealed some of the detailed structure of interstellar matter, in particular its patchiness. TD-1A, a European satellite, made an ultraviolet survey from 1972 to 1974 at 135–290 nm. ANS, the Astronomical Netherlands Satellite, made photometric observations of a large number of stars at 155–330 nm, also in the 1970s. Ultraviolet observations were carried out from the Skylab space station and the Voyager interplanetary probes, the latter covering the range 50–170 nm.
Ultraviolet astronomy entered a new era in 1978 with the launch of the International Ultraviolet Explorer (IUE), which obtained tens of thousands of spectra of various objects. Highlights include the discovery of hot haloes of gas surrounding our own and many other galaxies; the monitoring of mass loss by stellar winds in many different types of stars; and the study of the processes operating in novae and X-ray binaries. IUE also observed Halley’s Comet and contributed substantially to the understanding of Supernova 1987A.
The Hubble Space Telescope (HST) has extended the work of IUE, obtaining higher spectral resolution and observing significantly fainter objects. In addition, various ultraviolet telescopes have been carried in the cargo bay of the Space Shuttle. Ultraviolet astronomy has been carried into the extreme ultraviolet by Rosat and the Extreme Ultraviolet Explorer (EUVE). In 1999 the Far Ultraviolet Spectroscopic Explorer (FUSE) was launched to make high-resolution spectroscopic measurements in the 90–120 nm range. The Galaxy Evolution Explorer (GALEX) launched in 2003 has made imaging and spectroscopic surveys of galaxies in the near to far ultraviolet with a 0.5-m telescope. Some X-ray observatories such as XMM-Newton and Swift also cover part of the ultraviolet spectrum to complement the information gathered in X-rays.
http://photojournal.jpl.nasa.gov/catalog/PIA03033
The study of cosmic ultraviolet emissions using artificial satellites. The USA launched a series of satellites for this purpose, receiving the first useful data in 1968. Only a tiny percentage of solar ultraviolet radiation penetrates the atmosphere, this being the less dangerous longer-wavelength ultraviolet radiation. The dangerous shorter-wavelength radiation is absorbed by gases in the ozone layer high in the Earth's upper atmosphere.
The US Orbiting Astronomical Observatory (OAO) satellites provided scientists with a great deal of information regarding cosmic ultraviolet emissions. OAO-1, launched in 1966, failed after only three days, although OAO-2, put into orbit in 1968, operated for four years instead of the intended one year, and carried out the first ultraviolet observations of a supernova and also of Uranus. OAO-3 (Copernicus), launched in 1972, continued transmissions into the 1980s and discovered many new ultraviolet sources. The International Ultraviolet Explorer, which was launched in January 1978 and ceased operation in September 1996, observed all the main objects in the Solar System (including Halley's comet), stars, galaxies, and the interstellar medium. Since then, observations have moved into the extreme ultraviolet with ROSAT, the Extreme Ultraviolet Explorer, and the Far-Ultraviolet Spectroscopic Explorer, though all have since ceased operations. As of December 2017, only two ultraviolet satellites continue to explore the extreme ultraviolet Universe: Japan’s Hisaki (launched in 2013) and NASA’s MAVEN (launched in 2013), though MAVEN’s mission is designed to measure the variability of the solar soft X-rays and EUV irradiance at Mars.