United Kingdom Infrared Telescope, Infrared telescope on Mauna Kea, Hawaii County, US

The United Kingdom Infrared Telescope, also known as UKIRT, is an infrared telescope located near the summit of Mauna Kea on the island of Hawaii. Its primary mirror measures 3.8 m (12.5 ft) across, making it one of the larger single-mirror infrared telescopes of its kind.

The telescope was built in the mid-1970s and began operating in 1979 under the name Infrared Flux Collector before being renamed. It was originally funded by the Science and Engineering Research Council of the United Kingdom, which explains the British name it carries today.

The telescope's name reflects its origin: it was owned by the UK Science and Technology Facilities Council and run by the Joint Astronomy Centre in Hilo until 2014, when financial pressure led to its transfer to the University of Hawaii. About 60 nights a year are reserved for Korean institutes, and the wide-field survey UKIDSS consumed roughly 80% of observing time.

UKIRT stands near the summit of Mauna Kea, reached by a steep unpaved road that climbs from the Saddle Road; the summit road is normally driven in a four-wheel-drive vehicle. The air at this altitude is thin, so a stop at the Mauna Kea Visitor Information Station at about 2,800 m (9,200 ft) helps before continuing. The telescope building itself is a working facility and not open to casual visitors.

UKIRT's thin 6.5-tonne primary mirror sits in a 20-tonne steel cell and rests on 80 computer-controlled aluminium pneumatic pistons arranged in concentric circles. These air cells cancel stresses in the glass, letting a mirror far thinner than its contemporaries perform above its procurement specification.