UV astronomy
Encyclopedia
Ultraviolet astronomy is generally used to refer to observations of electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...

 at ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

 wavelengths between approximately 10 and 320 nanometres; shorter wavelengths—higher energy photons—are studied by X-ray astronomy
X-ray astronomy
X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and...

 and gamma ray astronomy. Light at these wavelengths is absorbed by the Earth's atmosphere, so observations at these wavelengths must be performed from the upper atmosphere or from space.

Ultraviolet line spectrum measurements are used to discern the chemical composition, densities, and temperatures of the interstellar medium
Interstellar medium
In astronomy, the interstellar medium is the matter that exists in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, dust, and cosmic rays. It fills interstellar space and blends smoothly into the surrounding intergalactic space...

, and the temperature and composition of hot young stars. UV observations can also provide essential information about the evolution of galaxies
Galaxy formation and evolution
The study of galaxy formation and evolution is concerned with the processes that formed a heterogeneous universe from a homogeneous beginning, the formation of the first galaxies, the way galaxies change over time, and the processes that have generated the variety of structures observed in nearby...

.

The ultraviolet Universe
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...

 looks quite different from the familiar star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

s and galaxies
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...

 seen in visible light.
Most stars are actually relatively cool objects emitting much of their electromagnetic radiation in the visible part of the spectrum. Ultraviolet radiation is the signature of hotter objects, typically in the early and late stages of their evolution
Stellar evolution
Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...

.
If we could see the sky in ultraviolet light, most stars would fade in prominence. We would see some very young massive stars and some very old stars and galaxies, growing hotter and producing higher-energy radiation near their birth or death. Clouds of gas and dust would block our vision in many directions along the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

.

The Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

 and FUSE
Far Ultraviolet Spectroscopic Explorer
The Far Ultraviolet Spectroscopic Explorer is a space-based telescope operated by the Johns Hopkins University Applied Physics Laboratory. FUSE was launched on a Delta II rocket on June 24, 1999, as a part of NASA's Origins program...

 have been the most recent major space telescopes to view the near and far UV spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....

 of the sky, though other UV instruments have flown on sounding rockets and the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

.

Ultraviolet space telescopes

(ESRO
ESRO
The European Space Research Organization was an international organisation founded by 10 European nations with the intention of jointly pursuing scientific research in space. It was founded in 1964...

) - TD-1A
TD-1A
TD-1A, or Thor-Delta 1A, was a European astrophysical research satellite which was launched in 1972. Operated by the European Space Research Organisation, TD-1A made astronomical surveys primarily in the ultraviolet, but also using x-ray and gamma ray detectors.-Spacecraft:TD-1A was named after the...

 - Astron-1
Astron (spacecraft)
Astron was a Soviet spacecraft launched on 23 March 1983 at 12:45:06 UTC, using Proton launcher, which was designed to fulfill an astrophysics mission. It was based on the Venera spacecraft design and was operational for six years as the largest ultraviolet space telescope during its lifetime...

 - Astrosat
Astrosat
Astrosat is India's first dedicated astronomy satellite and is scheduled to launch on board the PSLV in 2012. After the success of the satellite-borne Indian X-ray Astronomy Experiment , which was launched in 1996, the Indian Space Research Organization has approved further development for a full...

   - Astronomical Netherlands Satellite
Astronomical Netherlands Satellite
The Astronomical Netherlands Satellite was a space-based X-ray and ultraviolet telescope. It was launched into Earth orbit on 30 August 1974 at 14:07:39 UTC in a Scout rocket from Vandenberg Air Force Base, United States...

 (ESA) - Extreme ultraviolet Imaging Telescope
Extreme ultraviolet Imaging Telescope
The Extreme ultraviolet Imaging Telescope is an instrument on the SOHO spacecraft used to obtain high-resolution images of the solar corona in the ultraviolet range...

 - FUSE
Far Ultraviolet Spectroscopic Explorer
The Far Ultraviolet Spectroscopic Explorer is a space-based telescope operated by the Johns Hopkins University Applied Physics Laboratory. FUSE was launched on a Delta II rocket on June 24, 1999, as a part of NASA's Origins program...

 - GALEX
GALEX
The Galaxy Evolution Explorer is an orbiting ultraviolet space telescope launched on April 28, 2003. A Pegasus rocket placed the craft into a nearly circular orbit at an altitude of and an inclination to the Earth's equator of 29 degrees....

 (ESA) - Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...

 (ESA) - International Ultraviolet Explorer
International Ultraviolet Explorer
The International Ultraviolet Explorer was an astronomical observatory satellite primarily designed to take ultraviolet spectra. The satellite was a collaborative project between NASA, the UK Science Research Council and the European Space Agency...

 - Orbiting Astronomical Observatory
Orbiting Astronomical Observatory
The Orbiting Astronomical Observatory satellites were a series of four American space observatories launched by NASA between 1966 and 1972, which provided the first high-quality observations of many objects in ultraviolet light...

 - Swift Gamma-Ray Burst Mission
Swift Gamma-Ray Burst Mission
The Swift Gamma-Ray Burst Mission consists of a robotic spacecraft called Swift, which was launched into orbit on 20 November 2004, 17:16:00 UTC on a Delta II 7320-10C expendable launch vehicle. Swift is managed by the NASA Goddard Space Flight Center, and was developed by an international...

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