James Clerk Maxwell Telescope (JCMT)
The James Clerk Maxwell Telescope (JCMT) is currently the world's premier ground-based facility for astronomical observations at submillimetre wavelengths. This status is afforded by three essential ingredients: the size and quality of the telescope, its location, and its aggressive programme of instrumentation. Each of these is discussed in the following paragraphs.
The JCMT is the largest single-dish telescope in the world designed specifically to operate in the submillimetre region of the spectrum (wavelength range 300 ?m 3 mm). The primary reflector of the JCMT has a diameter of 15 metres and is made up of 276 individual lightweight panels. Each panel consists of a thin aluminium skin bonded to an aluminium honeycomb and is attached at three points to the backing structure of the antenna. The backing structure is designed to maintain a parabolic figure as gravity distorts the antenna as it tips to different elevations. The alignment of the individual panels can be adjusted by means of actuators at the mounting points. The sub-reflector, or secondary mirror, can be adjusted in three axes to compensate for changes in focus as well as changes in the figure of the primary. In addition, the secondary can be tilted or chopped in two axes in order to perform sky background cancellation.
The facility is situated at the summit of Mauna Kea, on the island of Hawaii, at an altitude of 4092 m. This is one of the best sites in the world for submillimetre astronomy, and certainly the very best in the northern hemisphere. The strongest constraint on ground-based observing at submillimetre wavelengths is the absorption of astronomical signals by water vapour in the Earth's atmosphere. The choice of site is vitally important in order to minimise this effect and to maximise the scientific productivity of the facility. Since the summit of Mauna Kea is the highest point in the Pacific Ocean, the telescope is physically above 97% of the water vapour in the atmosphere. Due to its distance from sources of industrial pollution and city light pollution as well as its exceptional weather characteristics, Mauna Kea is one of the premier observing sites in the world.
The JCMT TNA contact is I. Coulson
More information can be found on the JCMT Homepage.