James Clerk Maxwell Telescope
Encyclopedia
The James Clerk Maxwell Telescope (JCMT) is a submillimetre-wavelength
telescope at Mauna Kea Observatory
in Hawaii
. Its primary mirror is 15 metres (16.4 yards) across: it is the largest astronomical telescope that operates in submillimetre wavelengths of the electromagnetic spectrum (far-infrared
to microwave
). Scientists use it to study our Solar System
, interstellar dust
and gas
, and distant galaxies
.
The JCMT is funded by a partnership between the United Kingdom
, Canada
, and the Netherlands
. It is operated by the Joint Astronomy Centre
and was named in honour of mathematical physicist
James Clerk Maxwell
.
The telescope is near the summit of Mauna Kea
at 13,425 feet (4092 m). It is part of the Mauna Kea Observatory
. The JCMT has the second-largest telescope mirror on Mauna Kea. (The largest is the VLBA
antenna.)
This telescope was combined with the Caltech Submillimeter Observatory
to form the first submillimeter interferometer
. This success was important in pushing ahead the construction of the Submillimeter Array
and the Atacama Large Millimeter Array
interferometers.
(SRC, the forerunner of STFC
) considered the importance of astronomical observations at submillimetre and millimetre wavelengths. After a series of proposals and debates, in 1975, the SRC millimetre steering committee concluded that it would be possible to construct a 15-metre diameter telescope capable of observing at wavelengths down to 750 µm
. The project, then called the National New Technology Telescope (NNTT), was to be an 80/20 per cent collaboration with the Netherlands Organisation for the Advancement of Science. Site tests were made at Mauna Kea
in Hawaii
, the Pinaleno Mountains
in Arizona
, and a site in Chile
; and Mauna Kea was chosen. The NNTT is a unique facility, larger and with a more instruments than competing telescopes such as the CSO
and SMT
.
The final specifications called for the "world's largest telescope optimised for submillimetre wavelengths." It was to be a parabolic 15-metre antenna
composed of 276 individually adjustable panels with a surface accuracy of better than 50 µm. It would be an altitude-azimuth
mounted Cassegrain telescope with a tertiary mirror to direct the incoming radiation onto a number of different receivers. The antenna and mountings were to be protected from the elements by a co-rotating carousel with a transparent membrane stretched across the carousel aperture. Building work started in 1983 and went well apart from a small delay caused by the hijacking of the ship carrying the telescope across the Pacific by modern-day pirates. The telescope saw first light in 1987. The name for the final facility was changed to the James Clerk Maxwell
Telescope.
The JCMT is currently funded under a tripartite agreement between the United Kingdom
(55 percent), Canada
(25 percent), and the Netherlands
(20 percent). The telescope itself is operated by the Joint Astronomy Centre
(JAC), from Hilo, Hawaii. The telescope site agreement with the University of Hawaii
provides observer accommodation and infrastructure in exchange for open access to international proposals and 10 per cent of the observing time for the University's own projects. Proposals for telescope usage are submitted to one of the national Telescope Allocation Groups (TAGs) and if successful are awarded time in the next six-monthly semester.
—broadband
continuum
detectors and heterodyne detection
spectral-line receivers.
receiver was replaced in the 1990s by the Submillimetre Common-User Bolometer Array (SCUBA). The SCUBA project was greenlighted in 1987 by the JCMT board and was in development for nearly a decade before it saw first light on the telescope. While it was not the first bolometer-array
it was "unique in combining an unparallel sensitivity with an extensive wavelength range and field-of-view" http://xxx.lanl.gov/abs/astro-ph/9809122.
SCUBA is sensitive to the thermal emission
from interstellar dust
. This continuous emission
is a tracer of star formation
in other galaxies and gives astronomers clues to the presence, distance, and evolution history of galaxies
other than our own. Within our own galaxy
dust emission is associated with stellar nurseries
and planet forming solar systems.
SCUBA is ranked second only to the Hubble Space Telescope
in terms of publication of high-impact astronomical research. SCUBA was retired from service in 2005.
SCUBA-2, a replacement for SCUBA, has been commissioned in 2011. It has about 3000 array elements at both 450 and 850 micron wavelength.
and determine gas velocity gradients across astronomical objects (because of the doppler effect
). The spectral-line mapping capabilities of the JCMT have been greatly enhanced by the commissioning of HARP-B, a 350 GHz, 16 element heterodyne
array receiver. HARP-B, and the other heterodyne instruments, can be used in conjunction with the JCMT's new digital autocorrelation
spectrometer, ACSIS.
Submillimetre astronomy
Submillimetre astronomy or submillimeter astronomy is the branch of observational astronomy that is conducted at submillimetre wavelengths of the electromagnetic spectrum. Astronomers place the submillimetre waveband between the far-infrared and microwave wavebands, typically taken to be between a...
telescope at Mauna Kea Observatory
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...
in 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...
. Its primary mirror is 15 metres (16.4 yards) across: it is the largest astronomical telescope that operates in submillimetre wavelengths of the electromagnetic spectrum (far-infrared
Far infrared astronomy
Far-infrared astronomy is the branch of astronomy and astrophysics that deals with objects visible in far-infrared radiation ....
to 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...
). Scientists use it to study our Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
, interstellar dust
Cosmic dust
Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...
and gas
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 distant 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...
.
The JCMT is funded by a partnership between the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, and the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
. It is operated by the Joint Astronomy Centre
Joint Astronomy Centre
The Joint Astronomy Centre operates British, Canadian and Dutch telescopes at Mauna Kea Observatory, and provides support for other telescopes and public outreach activities...
and was named in honour of mathematical physicist
Mathematical physics
Mathematical physics refers to development of mathematical methods for application to problems in physics. The Journal of Mathematical Physics defines this area as: "the application of mathematics to problems in physics and the development of mathematical methods suitable for such applications and...
James Clerk Maxwell
James Clerk Maxwell
James Clerk Maxwell of Glenlair was a Scottish physicist and mathematician. His most prominent achievement was formulating classical electromagnetic theory. This united all previously unrelated observations, experiments and equations of electricity, magnetism and optics into a consistent theory...
.
The telescope is near the summit of Mauna Kea
Mauna Kea
Mauna Kea is a volcano on the island of Hawaii. Standing above sea level, its peak is the highest point in the state of Hawaii. However, much of the mountain is under water; when measured from its oceanic base, Mauna Kea is over tall—significantly taller than Mount Everest...
at 13,425 feet (4092 m). It is part of the Mauna Kea Observatory
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...
. The JCMT has the second-largest telescope mirror on Mauna Kea. (The largest is the VLBA
Very Long Baseline Array
The Very Long Baseline Array is a system of ten radio telescopes controlled remotely from the Array Operations Center in Socorro, New Mexico by the National Radio Astronomy Observatory. The array works together as the world's largest dedicated, full-time astronomical instrument using the...
antenna.)
This telescope was combined with the Caltech Submillimeter Observatory
Caltech Submillimeter Observatory
The Caltech Submillimeter Observatory is a diameter submillimeter wavelength telescope situated alongside the James Clerk Maxwell Telescope at Mauna Kea Observatory. It is engaged in submillimeter astronomy, of the terahertz radiation band.The CSO and JCMT were combined to form the first...
to form the first submillimeter interferometer
Astronomical interferometer
An astronomical interferometer is an array of telescopes or mirror segments acting together to probe structures with higher resolution by means of interferometry....
. This success was important in pushing ahead the construction of 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...
and 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...
interferometers.
History
In the late 1960s, the Astronomy Committee of the UK's Science Research CouncilResearch Council
The UK Research Councils, of which there are currently seven, are publicly-funded agencies responsible for co-ordinating and funding particular areas of research, including the arts, humanities, all areas of science and engineering...
(SRC, the forerunner of STFC
Science and Technology Facilities Council
The Science and Technology Facilities Council is a UK government body that carries out civil research in science and engineering, and funds UK research in areas including particle physics, nuclear physics, space science and astronomy .-History:It was formed in April 2007 as a merger of the Particle...
) considered the importance of astronomical observations at submillimetre and millimetre wavelengths. After a series of proposals and debates, in 1975, the SRC millimetre steering committee concluded that it would be possible to construct a 15-metre diameter telescope capable of observing at wavelengths down to 750 µm
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...
. The project, then called the National New Technology Telescope (NNTT), was to be an 80/20 per cent collaboration with the Netherlands Organisation for the Advancement of Science. Site tests were made at Mauna Kea
Mauna Kea
Mauna Kea is a volcano on the island of Hawaii. Standing above sea level, its peak is the highest point in the state of Hawaii. However, much of the mountain is under water; when measured from its oceanic base, Mauna Kea is over tall—significantly taller than Mount Everest...
in 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...
, the Pinaleno Mountains
Pinaleno Mountains
The Pinaleño Mountains, or the Pinal Mountains, are a remote mountain range in southeastern Arizona. They have over of vertical relief, more than any other range in the state. The mountains are surrounded by the Sonoran-Chihuahuan Desert. Subalpine forests cover the higher elevations...
in Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
, and a site in 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...
; and Mauna Kea was chosen. The NNTT is a unique facility, larger and with a more instruments than competing telescopes such as the CSO
Caltech Submillimeter Observatory
The Caltech Submillimeter Observatory is a diameter submillimeter wavelength telescope situated alongside the James Clerk Maxwell Telescope at Mauna Kea Observatory. It is engaged in submillimeter astronomy, of the terahertz radiation band.The CSO and JCMT were combined to form the first...
and SMT
Heinrich Hertz Submillimeter Telescope
The Submillimeter Telescope , formerly known as the Heinrich Hertz Submillimeter Telescope, is a submillimeter wavelength radio telescope located on Mount Graham, Arizona. It is a 10-meter-wide parabolic dish inside a building to protect it from bad weather. The building front doors and roof are...
.
The final specifications called for the "world's largest telescope optimised for submillimetre wavelengths." It was to be a parabolic 15-metre antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
composed of 276 individually adjustable panels with a surface accuracy of better than 50 µm. It would be an altitude-azimuth
Altazimuth mount
An altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two mutually perpendicular axes; one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth of the pointing direction of the instrument...
mounted Cassegrain telescope with a tertiary mirror to direct the incoming radiation onto a number of different receivers. The antenna and mountings were to be protected from the elements by a co-rotating carousel with a transparent membrane stretched across the carousel aperture. Building work started in 1983 and went well apart from a small delay caused by the hijacking of the ship carrying the telescope across the Pacific by modern-day pirates. The telescope saw first light in 1987. The name for the final facility was changed to the James Clerk Maxwell
James Clerk Maxwell
James Clerk Maxwell of Glenlair was a Scottish physicist and mathematician. His most prominent achievement was formulating classical electromagnetic theory. This united all previously unrelated observations, experiments and equations of electricity, magnetism and optics into a consistent theory...
Telescope.
The JCMT is currently funded under a tripartite agreement between the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
(55 percent), Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
(25 percent), and the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
(20 percent). The telescope itself is operated by the Joint Astronomy Centre
Joint Astronomy Centre
The Joint Astronomy Centre operates British, Canadian and Dutch telescopes at Mauna Kea Observatory, and provides support for other telescopes and public outreach activities...
(JAC), from Hilo, Hawaii. The telescope site agreement with the University of Hawaii
University of Hawaii
The University of Hawaii System, formally the University of Hawaii and popularly known as UH, is a public, co-educational college and university system that confers associate, bachelor, master, and doctoral degrees through three university campuses, seven community college campuses, an employment...
provides observer accommodation and infrastructure in exchange for open access to international proposals and 10 per cent of the observing time for the University's own projects. Proposals for telescope usage are submitted to one of the national Telescope Allocation Groups (TAGs) and if successful are awarded time in the next six-monthly semester.
Instrumentation
The JCMT has two kinds of instrumentsMeasuring instrument
In the physical sciences, quality assurance, and engineering, measurement is the activity of obtaining and comparing physical quantities of real-world objects and events. Established standard objects and events are used as units, and the process of measurement gives a number relating the item...
—broadband
Broadband
The term broadband refers to a telecommunications signal or device of greater bandwidth, in some sense, than another standard or usual signal or device . Different criteria for "broad" have been applied in different contexts and at different times...
continuum
Continuous spectrum
The spectrum of a linear operator is commonly divided into three parts: point spectrum, continuous spectrum, and residual spectrum.If H is a topological vector space and A:H \to H is a linear map, the spectrum of A is the set of complex numbers \lambda such that A - \lambda I : H \to H is not...
detectors and heterodyne detection
Heterodyne detection
Heterodyne detection is a method of detecting radiation by non-linear mixing with radiation of a reference frequency. It is commonly used in telecommunications and astronomy for detecting and analysing signals....
spectral-line receivers.
Continuum detectors
The older continuum single pixel UKT14 bolometerBolometer
A bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley...
receiver was replaced in the 1990s by the Submillimetre Common-User Bolometer Array (SCUBA). The SCUBA project was greenlighted in 1987 by the JCMT board and was in development for nearly a decade before it saw first light on the telescope. While it was not the first bolometer-array
Focal Plane Arrays
Focal Plane Arrays are arrays of receivers placed at the focus of a radio-telescope. Traditional radio-telescopes have only one receiver at the focus of the telescope, but radio-telescopes are now starting to be equipped with focal plane arrays, which are of three different types: multi-beam feed...
it was "unique in combining an unparallel sensitivity with an extensive wavelength range and field-of-view" http://xxx.lanl.gov/abs/astro-ph/9809122.
SCUBA is sensitive to the thermal emission
Thermal radiation
Thermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
from interstellar dust
Cosmic dust
Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...
. This continuous emission
Continuous spectrum
The spectrum of a linear operator is commonly divided into three parts: point spectrum, continuous spectrum, and residual spectrum.If H is a topological vector space and A:H \to H is a linear map, the spectrum of A is the set of complex numbers \lambda such that A - \lambda I : H \to H is not...
is a tracer 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...
in other galaxies and gives astronomers clues to the presence, distance, and evolution history 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...
other than our own. Within our own galaxy
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...
dust emission is associated with stellar nurseries
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...
and planet forming solar systems.
SCUBA is ranked second only to 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...
in terms of publication of high-impact astronomical research. SCUBA was retired from service in 2005.
SCUBA-2, a replacement for SCUBA, has been commissioned in 2011. It has about 3000 array elements at both 450 and 850 micron wavelength.
Spectral line detectors
The JCMT is also equipped with three heterodyne receivers, which allow submillimetre spectral-line observations to be made. Spectral-line observations can be used to identify particular molecules in molecular clouds, study their distribution and chemistryAstrochemistry
Astrochemistry is the study of the abundance and reactions of chemical elements and molecules in the universe, and their interaction with radiation. The discipline is an overlap of astronomy and chemistry. The word "astrochemistry" may be applied to both the Solar System and the interstellar medium...
and determine gas velocity gradients across astronomical objects (because of the doppler effect
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
). The spectral-line mapping capabilities of the JCMT have been greatly enhanced by the commissioning of HARP-B, a 350 GHz, 16 element heterodyne
Heterodyne
Heterodyning is a radio signal processing technique invented in 1901 by Canadian inventor-engineer Reginald Fessenden where high frequency signals are converted to lower frequencies by combining two frequencies. Heterodyning is useful for frequency shifting information of interest into a useful...
array receiver. HARP-B, and the other heterodyne instruments, can be used in conjunction with the JCMT's new digital autocorrelation
Autocorrelator
A real time interferometric autocorrelator is an electronic tool used to examine the autocorrelation of, among other things, optical beam intensity and spectral components through examination of variable beam path differences...
spectrometer, ACSIS.
See also
- Far infrared astronomyFar infrared astronomyFar-infrared astronomy is the branch of astronomy and astrophysics that deals with objects visible in far-infrared radiation ....
- Radio astronomyRadio astronomyRadio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
- SCUBA-2 All Sky SurveySCUBA-2 All Sky SurveyThe SCUBA-2 All-Sky Survey , is a major astronomical experiment using the James Clerk Maxwell Telescope in Hawaii. A team of around 50 astronomers from the United Kingdom, Canada, the United States, Netherlands, and Japan aim to map a huge swathe of the sky to find rare galaxies and stars being...
- Submillimetre astronomySubmillimetre astronomySubmillimetre astronomy or submillimeter astronomy is the branch of observational astronomy that is conducted at submillimetre wavelengths of the electromagnetic spectrum. Astronomers place the submillimetre waveband between the far-infrared and microwave wavebands, typically taken to be between a...