Annex: Space telescopes
This list of space telescopes (astronomical space observatories) is grouped by major frequency ranges: gamma-ray, X-ray, ultraviolet, visible, infrared, microwave, and radio. Telescopes operating in multiple frequency bands are included in all applicable sections. Space telescopes that collect particles, such as cosmic ray nuclei and/or electrons, are also listed, as well as instruments that aim to detect gravitational waves. Missions with specific targets within the Solar System (for example, our Sun and its planets) are excluded; see the list of space missions for these.
Two values are provided for the dimensions of the initial orbit. For telescopes in Earth orbit, the minimum and maximum altitude are given in kilometers. For telescopes in solar orbit, the minimum distance (periapsis) and maximum distance (apoapsis) between the telescope and the sun's center of mass are given in astronomical units (AU).
Gamma-ray telescopes collect and measure single, high-energy gamma rays from astrophysical sources. These are absorbed by the atmosphere, requiring observations to be made by high-altitude balloons or space missions. Gamma rays can be generated by supernovae, neutron stars, pulsars, and black holes. Gamma-ray bursts, with extremely high energies, have also been detected but not yet identified.
X-ray telescopes measure high-energy photons called X-rays. These cannot travel a long distance through the atmosphere, which means they can only be observed high in the atmosphere or in space. Various types of astrophysical objects emit X-rays, from galaxy clusters, through black holes in active galactic nuclei to galactic objects such as supernova remnants, stars and binary stars containing a white dwarf (cataclysmic variable star), neutron star or black hole (X-ray binaries). Some bodies in the Solar System emit X-rays, most notably the Moon, although most of the Moon's X-ray brightness arises from reflected Solar X-rays. A combination of many unresolved X-ray sources is thought to produce the observed X-ray background.
Ultraviolet telescopes make observations in ultraviolet wavelengths, that is, between about 10 and 320 nm. Light at these wavelengths is absorbed by the Earth's atmosphere, so observations at these wavelengths must be made from the upper atmosphere or from space. Objects that emit ultraviolet radiation include the Sun , other stars and galaxies.
The oldest form of astronomy, optical or visible-light astronomy, observes wavelengths of light from approximately 400 to 700 nm. Placing an optical telescope in space removes the distortions and limitations that hinder telescopes. terrestrial optics (see observational astronomy), providing higher resolution images. Optical telescopes are used to observe planets, stars, galaxies, planetary nebulae, and protoplanetary disks, among many other things.
Infrared and submillimeter
Infrared light is of lower energy than visible light, therefore it is emitted by sources that are cooler or moving away from the observer (in today's context: Earth) at high speed. As such, the following can be seen in the infrared: cool stars (including brown dwarfs), nebulae, and redshifted galaxies.
Microwave space telescopes have