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Submillimetre astronomy

Submillimetre astronomy

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Submillimetre astronomy or submillimeter astronomy (see spelling differences) is the branch of observational astronomy
Observational astronomy
Observational astronomy is a division of the astronomical science that is concerned with getting data, in contrast with theoretical astrophysics which is mainly concerned with finding out the measurable implications of physical models...

 that is conducted at submillimetre wavelengths
Terahertz radiation
In physics, terahertz radiation refers to electromagnetic waves propagating at frequencies in the terahertz range. It is synonymously termed submillimeter radiation, terahertz waves, terahertz light, T-rays, T-waves, T-light, T-lux, THz...

 of the electromagnetic 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....

. Astronomers place the submillimetre waveband between the far-infrared and microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...

 wavebands, typically taken to be between a few hundred micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...

s and a millimetre
Millimetre
The millimetre is a unit of length in the metric system, equal to one thousandth of a metre, which is the SI base unit of length....

. It is still common in submillimetre astronomy to quote wavelengths in 'microns', the old name for micrometre.

Using submillimetre observations, astronomers examine molecular cloud
Molecular cloud
A molecular cloud, sometimes called a stellar nursery if star formation is occurring within, is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen ....

s and dark cloud cores with a goal of clarifying the process of star formation
Star formation
Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. As a branch of astronomy star formation includes the study of the interstellar medium and giant molecular clouds as precursors to the star formation process and the study of young...

 from earliest collapse
Gravitational collapse
Gravitational collapse is the inward fall of a body due to the influence of its own gravity. In any stable body, this gravitational force is counterbalanced by the internal pressure of the body, in the opposite direction to the force of gravity...

 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
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...

.

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
Mauna Kea Observatory
The Observatories at Mauna Kea, , are an independent collection of astronomical research facilities located on the summit of Mauna Kea on the Big Island of Hawai'i, USA. The facilities are located in a special land use zone known as the "Astronomy Precinct," which is located in the Mauna Kea...

 (Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

, USA), the Llano de Chajnantor Observatory
Llano de Chajnantor Observatory
Llano de Chajnantor Observatory is an astronomical observatory located at an altitude of 5,104 m in the Chilean Atacama desert, 50 kilometers to the east of San Pedro de Atacama. It is a very dry site - inhospitable to humans - but an excellent site for submillimetre astronomy...

 on the Atacama Plateau (Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

), the South Pole
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...

, and Hanla (India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

). 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
Llano de Chajnantor Observatory
Llano de Chajnantor Observatory is an astronomical observatory located at an altitude of 5,104 m in the Chilean Atacama desert, 50 kilometers to the east of San Pedro de Atacama. It is a very dry site - inhospitable to humans - but an excellent site for submillimetre astronomy...

 site hosts the Atacama Pathfinder Experiment
Atacama Pathfinder Experiment
The Atacama Pathfinder Experiment is a radio telescope located at 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert, in northern Chile, 50 kilometers to the east of San Pedro de Atacama. The main dish has a diameter of 12 meters and consists of 264...

 (APEX), the largest submillimetre telescope operating in the southern hemisphere,
and the world's largest ground based astronomy project, the Atacama Large Millimeter Array
Atacama Large Millimeter Array
The Atacama Large Millimeter/sub-millimeter Array is an array of radio telescopes in the Atacama desert of northern Chile. Since a high and dry site is crucial to millimeter wavelength operations, the array is being constructed on the Chajnantor plateau at 5000 metres altitude...

 (ALMA), an interferometer
Interferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...

 for submillimetre wavelength observations made of 54 12-metre and 12 7-metre radio telescopes. The Submillimeter Array
Submillimeter Array
The Submillimeter Array consists of eight diameter radio telescopes arranged as an interferometer for submillimeter wavelength observations. It is the first purpose-built submillimeter interferometer, constructed after successful interferometry experiments using the pre-existing James Clerk...

 (SMA) is another interferometer
Interferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...

, located at Mauna Kea, consisting of eight 6-metre diameter radio telescopes. The largest existing submillimetre telescope, the James Clerk Maxwell Telescope
James Clerk Maxwell Telescope
The James Clerk Maxwell Telescope is a submillimetre-wavelength telescope at Mauna Kea Observatory in Hawaii. Its primary mirror is 15 metres across: it is the largest astronomical telescope that operates in submillimetre wavelengths of the electromagnetic spectrum...

, is also located on Mauna Kea.

Submillimetre astronomy from near-space


With high-altitude balloons and aircraft, one can get above even more of the atmosphere. The BLAST
BLAST (telescope)
The Balloon-borne Large Aperture Submillimeter Telescope is a submillimeter telescope that hangs from a high altitude balloon. It has a 2 meter primary mirror that directs light into bolometer arrays operating at 250, 350, and 500 µm. These arrays were developed for the SPIRE instrument on the...

 experiment and SOFIA
Sofia
Sofia is the capital and largest city of Bulgaria and the 12th largest city in the European Union with a population of 1.27 million people. It is located in western Bulgaria, at the foot of Mount Vitosha and approximately at the centre of the Balkan Peninsula.Prehistoric settlements were excavated...

 are two examples, respectively, although SOFIA can also handle near infrared observations.

Submillimetre astronomy from space


Space-based observations at the submillimetre wavelengths remove the ground-based limitations of atmospheric absorption. The Submillimeter Wave Astronomy Satellite
Submillimeter Wave Astronomy Satellite
The Submillimeter Wave Astronomy Satellite was an astronomical observatory launched on December 5, 1998 as part of the Small Explorer program within NASA...

 (SWAS) was launched into low Earth orbit on December 5, 1998 as one of NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

'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
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 (H2O), isotopic water (H218O), isotopic carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 (13CO), molecular oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 (O2), and neutral carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 (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
European Space Agency
The European Space Agency , established in 1975, is an intergovernmental organisation dedicated to the exploration of space, currently with 18 member states...

 launched a space-based mission known as the Herschel Space Observatory
Herschel Space Observatory
The Herschel Space Observatory is a European Space Agency space observatory sensitive to the far infrared and submillimetre wavebands. It is the largest space telescope ever launched, carrying a single mirror of in diameter....

 (formerly called Far Infrared and Sub-millimetre Telescope or FIRST) in 2009. Herschel deploys the largest mirror ever launched into space and studies radiation in the far infrared and submillimetre wavebands. Rather than an Earth orbit, Herschel entered into a Lissajous orbit
Lissajous orbit
In orbital mechanics, a Lissajous orbit, , named after Jules Antoine Lissajous, is a quasi-periodic orbital trajectory that an object can follow around a Lagrangian point of a three-body system without requiring any propulsion. Lyapunov orbits around a libration point are curved paths that lie...

 around , the second Lagrangian point
Lagrangian point
The Lagrangian points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects...

 of the Earth-Sun system. is located approximately 1.5 million km from Earth and the placement of Herschel there lessens the interference by infrared and visible radiation from the Earth and Sun. Herschel's mission focuses primarily on the origins of galaxies and galactic formation.

See also

  • Far infrared astronomy
    Far infrared astronomy
    Far-infrared astronomy is the branch of astronomy and astrophysics that deals with objects visible in far-infrared radiation ....

  • SOFIA
    Sofia
    Sofia is the capital and largest city of Bulgaria and the 12th largest city in the European Union with a population of 1.27 million people. It is located in western Bulgaria, at the foot of Mount Vitosha and approximately at the centre of the Balkan Peninsula.Prehistoric settlements were excavated...

  • Radio window
    Radio window
    The radio window is the range of frequencies of electromagnetic radiation that the earth's atmosphere lets through. The wavelengths in the radio window run from about one centimetre to about eleven-metre waves.-See also:*Astronomical window...

  • Atmospheric window
    Atmospheric window
    The infrared atmospheric window is the overall dynamic property of the earth's atmosphere, taken as a whole at each place and occasion of interest, that lets some infrared radiation from the cloud tops and land-sea surface pass directly to space without intermediate absorption and re-emission, and...

  • Astronomical window
  • Optical window
    Optical window
    The meaning of this term depends on the context:* In astronomy, the optical window is the optical portion of the electromagnetic spectrum that passes through the atmosphere all the way to the ground...

  • :Category:Submillimetre telescopes

External links