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Submillimetre astronomy

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Submillimetre astronomy or submillimeter astronomy (see spelling differences) is the branch of observational astronomy that is conducted at submillimetre wavelengths. It is often described as residing in the far-infrared or between the infrared and radio wavebands. Astronomers place the submillimetre waveband between the far-infrared and microwave wavebands, typically taken to be between a few hundred micrometres and a millimetre. It is still common in submillimetre astronomy to quote wavelengths in 'microns', the old name for micrometer.

Using submillimetre observations, astronomers examine molecular clouds and dark cloud cores with a goal of clarifying the process of star formation from earliest collapse to stellar birth. Space-based observations of these dark clouds will attempt to determine chemical abundances and cooling mechanisms for the molecules which comprise them. In addition, submillimetre observations will attempt to determine the mechanisms for the formation and evolution of galaxies.

Submillimetre astronomy from the ground

The most significant limitation to the detection of astronomical emission at submillimetre wavelengths with ground based observatories is atmospheric emission, noise and attenuation. Like the infrared, the submillimetre atmosphere is dominated by numerous water vapour absorption bands and it is only through "windows" between these bands that observations are possible. The ideal submillimetre observing site is dry, cool, has stable weather conditions and is away from urban population centres. There are only a handful of such sites identified, they include Mauna Kea (Hawaii, USA), the Llano de Chajnantor Observatory on the Atacama Plateau (Chile), the South Pole, and Hanla (India). Comparisons show that all four sites are excellent for submillimetre astronomy, and of these sites Mauna Kea is the most established and arguably the most accessible. The Llano de Chajnantor Observatory site will soon host the worlds largest groundbased astronomy project, the Atacama Large Millimeter Array for millimetre and submillimetre astronomy. The Submillimeter Array (SMA) located at Mauna Kea consists of eight 6-metre diameter radio telescopes arranged as an interferometer for submillimetre wavelength observations. The largest existing submillimetre telescope, the James Clerk Maxwell Telescope, is also located on Mauna Kea.

Submillimetre astronomy from space

Space-based observations at the submillimetre wavelengths remove the ground-based limitations of atmospheric absorption. The Submillimeter Wave Astronomy Satellite (SWAS) was launched into low Earth orbit on December 5, 1998 as one of NASA's Small Explorer Program (SMEX) missions. The mission of the spacecraft is to make targeted observations of giant molecular clouds and dark cloud cores. The focus of SWAS is five spectral lines: water (H2O), isotopic water (H218O), isotopic carbon monoxide (13CO), molecular oxygen (O2), and neutral carbon (C I).

The SWAS satellite was repurposed in June, 2005 to provide support for the NASA Deep Impact mission. SWAS provided water production data on the comet until the end of August 2005.

The European Space Agency plans a space-based mission known as the Herschel Space Observatory (formerly called Far Infrared and Sub-millimetre Telescope or FIRST) for 2007. Herschel will deploy the largest mirror ever launched into space and study radiation in the far infrared and submillimetre wavebands. Rather than an Earth orbit, Herschel will enter into a Lissajous orbit around L2, the second Lagrangian point of the Earth-Sun system. L2 is located approximately 1.5 million km from Earth and the placement of Herschel there will lessen the interference by infrared and visible radiation from the Earth and Sun. Herschel's mission will focus primarily on the origins of galaxies and galactic formation.

See also

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