equatorial mounting

equatorial mounting

equatorial mounting: see telescope.
UKIRT, the United Kingdom Infra-Red Telescope, is a 3.8 metre (150 inch) infrared reflecting telescope, the largest dedicated infrared (1 to 30 micrometre) telescope in the world. It is operated by the Joint Astronomy Centre in Hilo and located on Mauna Kea, Hawai'i as part of Mauna Kea Observatory. It is owned by the United Kingdom Science and Technology Facilities Council.

Based on the design of the Carlos Sanchez Telescope in Tenerife it is a Cassegrain device with a thin primary mirror, around 2/3 thinner than in other contemporary devices and weighing only 6.5 tonnes. The mirror is held in a massive steel 'cell' of 20 tonnes which is linked to the supports by Serrurier trusses. The instrument is held and pointed by a massive 'English Equatorial mounting' or yoke which sits on ball-bearings on steel piers, swinging east-west and rotating around north-south. The geometry of the mount limits the telescopes access to objects between +60 and -40 degrees of declination but it is extremely sturdy and free from deformation and so allows very accurate pointing. The telescope was built between 1975 and 1978; the mechanical systems were built by Dunford Hadfields of Sheffield and the optics by Grubb Parsons of Newcastle. Originally known as the Infrared Flux Collector it began operation in October 1979.


UKIRT has three Cassegrain instruments and a wide-field imager placed forward of the Cassegrain focus.

  • CGS4 is a cooled-grating spectrometer with a 90-arcsecond long slit, at spectral resolutions between about 1,000 and 30,000.
  • UFTI is a 1024x1024 pixel imager operating between 0.8 and 2.5 micrometres.
  • UIST is a 1024x1024 pixel imager/spectrometer operating between 0.8 and 5 micrometres, and offering an integral field mode 3x6 arcseconds in size.
  • WFCAM (at forward Cassegrain) is a wide-field imager with four 2048x2048 arrays, each of which covers a field 13.6 arcminutes on a side, for a total field of view of about 0.2 square degrees.


Built as a relatively cheap telescope, UKIRT has been extensively upgraded. A program of improvements from 1990 to 1998 greatly improved the imaging performance, and in 2001 the telescope delivered median infrared seeing ranging from 0.8 arcseconds at dusk to 0.5 arcseconds in the early morning Between 1998 and 2003, two major software projects were undertaken - the ORAC project providing a major upgrade to the user interface and automating telescope operations, and the OMP providing a comprehensive observation database and data feedback mechanisms. Since 2003, using these two software enhancements, UKIRT has carried out highly efficient flexible scheduling - tailoring observation execution to the prevailing weather conditions. Observations are selected from the database according to the current seeing, atmospheric water vapour, sky transparency and a science priority allocated by the telescope time allocation panel.

Current operations

With the delivery of the wide-field imager WFCAM in 2004, UKIRT began a revolutionary large-scale sky survey (the UKIRT Infrared Deep Sky Survey, UKIDSS). This project takes some 80% of the available telescope time in wide-field mode. Wide-field takes some 60% of the telescope; the other 40% is devoted to operations with the Cassegrain instrumentation.

External links

  • http://www.jach.hawaii.edu/UKIRT
  • http://www.jach.hawaii.edu/UKIRT/telescope/telescope.html
  • http://www.ukidss.org/

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