William Herschel Telescope (WHT) at night. The WHT is situated at the Roque de los Muchachos Observatory on La Palma in the Canary Islands. With a diameter of 4.2 metres, this telescope's aluminium-coated primary mirror is one of the largest in the world. It is used to make observations from ultraviolet to infrared wavelengths (300-1100 nanometres). The telescope is placed on an alt-azimuthal mounting. It stands at an altitude of about 2300 metres to reduce atmospheric distortions to incoming light. The WHT was commissioned in 1987 and is run by the Royal Greenwich Observatory as part of the Isaac Newton Group (ING) of telescopes.