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The Atacama Cosmology Telescope (ACT) is a six-metre telescope on Cerro Toco in the Atacama Desert in the north of Chile, near the Llano de Chajnantor Observatory. It is designed to make high-resolution, microwave-wavelength surveys of the sky in order to study the cosmic microwave background radiation (CMB). At an altitude of 5190 metres (17,030 feet), it is one of the highest permanent, ground-based telescopes in the world.〔The Receiver Lab Telescope (RLT), an 80 cm instrument, is higher at 5525 m, but is not permanent as it is fixed to the roof of a movable shipping container. The new University of Tokyo Atacama Observatory is significantly higher than both.〕 Erected in the (austral) autumn of 2007, ACT saw first light on 22 October 2007 with its science receiver, the Millimeter Bolometer Array Camera (MBAC), and completed its first season in December 2007. It began its second season of observations in June 2008. The project is a collaboration between Princeton University, Cornell University, the University of Pennsylvania, NASA/GSFC, the Johns Hopkins University, the University of British Columbia, NIST, the Pontificia Universidad Católica de Chile, the University of KwaZulu-Natal, Cardiff University, Rutgers University, the University of Pittsburgh, Columbia University, Haverford College, INAOE, LLNL, NASA/JPL, the University of Toronto, the University of Cape Town, the University of Massachusetts Amherst and York College, CUNY. It is funded by the US National Science Foundation. ==Design and location== The ACT is an off-axis Gregorian telescope, with a six metre (236 in) primary mirror and a two metre (79 in) secondary mirror. Both mirrors are segmented, consisting of 71 (primary) and 11 (secondary) aluminum panels. Unlike most telescopes which track the rotating sky during observation, the ACT observes a strip of sky, typically five degrees wide, by scanning back and forth in azimuth at the relatively rapid rate of two degrees per second. The rotating portion of the telescope weighs approximately 32 tonnes (35 short tons), creating a substantial engineering challenge. A ground screen surrounding the telescope minimises contamination from microwave radiation emitted by the ground. The design, manufacture and construction of the telescope were done by (Dynamic Structures ) in Vancouver, British Columbia. Observations are made at resolutions of about an arcminute (1/60th of a degree) in three frequencies: 145 GHz, 215 GHz and 280 GHz. Each frequency is measured by a 3 cm x 3 cm (1.2" x 1.2"), 1024 element array, for a total of 3072 detectors. The detectors are superconducting ''transition-edge sensors'', a new technology whose high sensitivity should allow measurements of the temperature of the CMB to within a few millionths of a degree.〔 〕 A system of cryogenic helium refrigerators keep the detectors a third of a degree above absolute zero. In its currently scheduled survey, the ACT will map about two hundred square degrees of the sky.〔 〕 Because water vapour in the atmosphere emits microwave radiation which contaminates measurements of the CMB, the telescope benefits from its arid, high-altitude site, located in the lofty—yet easily accessible—Chajnantor plain in the Andean mountains in the Atacama Desert. Several other observatories are located in the region, including CBI, ASTE, Nanten, APEX and ALMA. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Atacama Cosmology Telescope」の詳細全文を読む スポンサード リンク
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