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Joint Astronomy Centre Outreach - James Clerk Maxwell Telescope
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The James Clerk Maxwell Telescope

The James Clerk Maxwell Telescope (JCMT) is one of two telescopes operated by the Joint Astronomy Centre, the other being the United Kingdom Infrared Telescope (UKIRT).

The JCMT on Mauna Kea.

The JCMT is the largest single-dish telescope in the world dedicated to detecting submillimetre radiation. Its 15-metre (50-foot) dish looks at the sky with instruments that tell us about the cold Universe in different ways. Operating between the infrared and radio waves, it uses some of the most sensitive and sophisticated instrumentation to detect the coldest material in the Universe, only a few tens of degrees above absolute zero. Water vapour in the Earth’s atmosphere intercepts this radiation, making the high and dry site of Mauna Kea vitally important for the research performed at the JCMT.

The JCMT looks upward and outward.

The JCMT's dish, as wide as a basketball court, collects the submillimetre light and feeds it to a set of sensitive detectors. The dish is protected from wind, sand and birds by a sailcloth-like membrane or Gore-Tex.

The JCMT's dish.

In between the stars are giant clouds where stars and solar systems are born. They are made of gas (mostly hydrogen) and cosmic dust (tiny particles of silicate and carbon). The clouds are some of the coldest objects in the Universe - so cold that their "heat glow" is invisible to human eyes. We need specialised telescopes and instruments to see this submillimetre radiation.

SCUBA-2 arrives at the JCMT (April 2008).

The newest instrument on the JCMT is SCUBA-2 which is the most powerful camera of its kind. New technology and novel design means it can map the sky faster than its predecessor, SCUBA. SCUBA-2 has 5120 pixels (4 sub arrays x 1280 pixels) at two wavelengths. Sensitivity requirements mean that these detectors within SCUBA-2 are cooled to temperatures just less than 0.1K = -272.9°C = -459.2°F

SCUBA-2 begins science operation (late 2011)

The SCUBA-2 instrument is keeping the JCMT at the forefront of submillimetre astronomy, complementing the Submillimeter Array on Mauna Kea and forthcoming telescopes such as the Atacama Large Millimeter Array in Chile.

The JCMT also has 'heterodyne receivers' which detect light from gas molecules in space. These molecules emit characteristic submillimetre radiation patterns when they rotate. The patterns are 'fingerprints' that tell us about the temperature, density, or motion of the gas. HARP is such an instrument which combines a camera and a spectrometer. This means we can learn about the chemistry of interstellar gas, its temperature, density and motion.


The nearest massive star formation to Earth is happening 1500 light years away in the constellation of Orion, the Hunter. In this cloud new stars are born, and into this stars disperse or explode as they die. HARP's images of Orion show the presence of carbon monoxide. The bright region in the center reveals new star formation. Evident is the surrounding gas undergoing streaming motions both to and away from the region.

The JCMT is internationally funded by the UK and Canada. It was opened in April 1987.

You can find some more technical information in a previous article about the JCMT.

Contact: JAC outreach. Updated: Mon Apr 1 08:08:18 HST 2013

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