Ultraviolet astronomy

Matter in the universe emits radiation (energy in the form of subatomic particles or waves) from all parts of the electromagnetic spectrum. The electromagnetic spectrum is the range of wavelengths produced by the interaction of electricity and magnetism. The electromagnetic spectrum includes light waves, radio waves, infrared radiation, ultraviolet radiation, X rays, and gamma rays.

Ultraviolet astronomy is the study of celestial matter that emits ultraviolet radiation. Ultraviolet waves are just shorter than the violet end (shortest wavelength) of the visible light spectrum. This branch of astronomy has provided additional information about stars (including the Sun), galaxies, the solar system, the interstellar medium (the "empty" space between celestial bodies), and quasars.

Words to Know

Electromagnetic radiation: Radiation that transmits energy through the interaction of electricity and magnetism.

Gamma rays: Short-wavelength, high-energy radiation formed either by the decay of radioactive elements or by nuclear reactions.

Infrared radiation: Electromagnetic radiation of a wavelength shorter than radio waves but longer than visible light that takes the form of heat.

Quasars: Extremely bright, starlike sources of radio waves that are the oldest known objects in the universe.

Radiation: Energy transmitted in the form of subatomic particles or waves.

Radio waves: Longest form of electromagnetic radiation, measuring up to 6 miles (9.7 kilometers) from peak to peak.

Ultraviolet radiation: Electromagnetic radiation of a wavelength just shorter than the violet (shortest wavelength) end of the visible light spectrum.

Wavelength: The distance between two troughs or two peaks in any wave.

X rays: Electromagnetic radiation of a wavelength just shorter than ultraviolet radiation but longer than gamma rays that can penetrate solids and produce an electrical charge in gases.

An ultraviolet telescope is similar to an optical telescope, except for a special coating on the lens. Due to Earth's ozone layer, which filters out most ultraviolet rays, ultraviolet astronomy is impossible to conduct on the ground. In order to function, an ultraviolet telescope must be placed on a satellite orbiting beyond Earth's atmosphere.

Information collected by ultraviolet telescopes

Beginning in the 1960s, a series of ultraviolet telescopes have been launched on spacecraft. The first such instruments were the eight Orbiting Solar Observatories placed into orbit between 1962 and 1975. These satellites measured ultraviolet radiation from the Sun. The data collected from these telescopes provided scientists with a much more complete picture of the solar corona, the outermost part of the Sun's atmosphere.

The Orbiting Astronomical Observatories (OAO) were designed to provide information on a variety of subjects, including thousands of stars, a comet, a nova in the constellation Serpus, and some galaxies beyond

the Milky Way. Between 1972 and 1980, OAO Copernicus collected information on many stars as well as the composition, temperature, and structure of interstellar gas.

The most successful ultraviolet satellite to date was the International Ultraviolet Explorer (IUE) launched in 1978. The IUE was a joint project of the United States, Great Britain, and the European Space Agency. With very sensitive equipment, the IUE studied planets, stars, galaxies, nebulae, quasars, and comets. It recorded especially valuable information from novae and supernovae. Although intended to function for only three to five years, the IUE operated until September 30, 1996, making it the longest-lived astronomical satellite.

The IUE was succeeded by the Extreme Utraviolet Explorer (EUEV), which was launched on June 7, 1992. The EUEV was designed to extend the spectral coverage of the IUE by being able to observe much shorter wavelengths. A third ultraviolet satellite, the Far Ultraviolet Spectroscopic Explorer (FUSE), was launched on June 24, 1999. This satellite also was designed to look farther into the ultraviolet (meaning to shorter wavelengths) than the IUE. With FUSE, astronomers hope to study high-energy processes in stars and galaxies in addition to exploring conditions in the universe as they existed only shortly after the big bang (theory that explains the beginning of the universe as a tremendous explosion from a single point that occurred 12 to 15 billion years ago).

[See also Electromagnetic spectrum; Galaxy; International Ultra violet Explorer; Telescope ]

ultraviolet astronomy The study of the Universe in the ultraviolet region of the electromagnetic spectrum, approximately 91.2–350 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.