A space observatory is any object in outer space which is used for observation of distant planets, galaxies, and other outer space objects. A large number of observatories have been launched into orbit, and most of them have greatly enhanced our knowledge of the cosmos. Performing astronomy from the Earth's surface is limited by the filtering and distortion of electromagnetic radiation due to the Earth's atmosphere. This makes it desirable to place astrononomical observation devices into space. As a telescope orbits the Earth outside the atmosphere it is neither subject to twinkling (distortion due to thermal turbulences of the air) nor to light pollution from artificial light sources on the Earth. Some terrestrial telescopes (such as the Very Large Telescope) can counter turbulences with the help of its novel adaptive optics.
But space-based astronomy is even more important for frequency ranges which are outside of the optic window and the radio window, as the two only wavelength ranges of the electromagnetic spectrum are called, that are not severely attenuated by the atmosphere. For example, X-ray astronomy is nearly impossible when done from the Earth, and has reached its current important stand within astronomy only due to orbiting satellites with X-ray telescopes such as the Chandra observatory. Infrared and ultraviolet are also greatly blocked.
Space observatories can generally be divided into two classes: missions which map the entire sky (surveys), and observatories which make observations of chosen parts of the sky.
NASA's Great Observatories
Satellites belonging to NASA's "Great Observatories" program:
- The Space Telescope (ST), now known as Hubble Space Telescope (HST) is the optical Great Observatory. It was launched to great acclaim and soon after discovered to be flawed. Its main mirror contained imperfections in its grinding that resulted from a certain production limitation being accounted for twice. It has now been fitted with the equivalent of spectacles to compensate for this.
- The Gamma ray Observatory (GRO), since renamed to The Compton Gamma-Ray Observatory, had to be disposed of after several years of productive life. Its gyroscopes began to fail and when it was down to its last gyroscope, the choice was to risk losing control or destroying the observatory. NASA ditched the bus-sized satellite into the Pacific Ocean in 2000.
- X-Rays are also represented in the Great Observatories, with the Chandra X-ray Observatory, renamed (from AXAF) in honor of the great Indian astrophysicist Chandrasekhar. This has been used to great effect to study distant galaxies and is still operational.
- The Spitzer Space Telescope is the fourth observatory, originally called the Space Infrared Telescope Facility, SIRTF, launched on August 24, 2003.
- The James Webb Space Telescope is intended to replace the Hubble Space Telescope and is planned for launch between 2009 and 2011.
Other notable space observatories
- IRAS, which performed an all-sky survey in infrared, as well as discovering disks of dust and gas around many nearby stars, such as Fomalhaut, Vega and Beta Pictoris. This ceased functioning in 1982 and has since re-entered the atmosphere.
- ISO (Infrared Space Observatory), an ESA (European Space Agency) mission, followed IRAS and carried out observations at infra-red wavelengths.
- IUE (International Ultraviolet Explorer ), an ESA/NASA/UK observatory that was launched in 1978 with a planned lifetime of 3 years. It was eventually switched off in 1996.
- SOHO is a solar observatory, it is operational and used for the study of the Sun's corona and magnetic environments. SOHO has revolutionised our knowledge of the Sun.
- SCISAT-1 is a Canadian satellite which observes Earth's upper atmosphere with an optical Fourier transform infrared spectrometer.
- HEAO (High Energy Astronomy Observatories) 1 and 2, subsequent (1978) X-Ray space observatories
- Hipparcos was a satellite for measuring stellar parallax. Despite significant operational problems, it revised the Cepheid variable star distance scale to great accuracy and has been invaluable for all branches of observational astronomy by furnishing scientists with extremely accurate "standard candles" for measuring distances.
- MOST was launched in 2003 for the Canadian Space Agency and it is the smallest space telescope in the world, being the size of a small chest or a very large suitcase. It is expected to last five years.
- Timeline of artificial satellites and space probes
- Timeline of telescopes, observatories, and observing technology