The William Herschel Telescope (WHT) is a optical/near-infrared reflecting telescope located at the Roque de los Muchachos Observatory on the island of La Palma in the Canary Islands, Spain. The telescope, which is named after William Herschel, the discoverer of the planet Uranus, is part of the Isaac Newton Group of Telescopes. It is funded by research councils from the United Kingdom, the Netherlands and Spain. At the time of construction in 1987, the WHT was the third largest single optical telescope in the world. It is currently the second largest in Europe, and was the last telescope constructed by Grubb Parsons in their 150-year history. The WHT is equipped with a wide range of instruments operating over the optical and near-infrared regimes. These are used by professional astronomers to conduct a wide range of astronomical research. Astronomers using the telescope discovered the first evidence for a supermassive black hole (Sgr A*) at the centre of the Milky Way, and made the first optical observation of a gamma-ray burst. The telescope has 75% clear nights, with a median seeing of 0.7". History The WHT was first conceived in the late 1960s, when the Anglo-Australian Telescope (AAT) was being designed. The British astronomical community saw the need for telescopes of comparable power in the northern hemisphere. In particular, there was a need for optical follow-up of interesting sources in the radio surveys being conducted at the Jodrell Bank and Mullard observatories (both located in the UK), which could not be done from the southern hemisphere location of the AAT. The AAT was completed in 1974, at which point the British Science and Engineering Research Council began planning for a group of three telescopes located in the northern hemisphere (now known as the Isaac Newton Group of Telescopes, ING). The telescopes were to be a (which became the Jacobus Kapteyn Telescope), the Isaac Newton Telescope which was to be moved from its existing site at Herstmonceux Castle, and a 4m class telescope, initially planned as a . A new site was chosen at an altitude of on the island of La Palma in the Canary Islands, that is now the Roque de los Muchachos Observatory. The project was led by the Royal Greenwich Observatory (RGO), who also operated the telescopes until control passed to an independent ING when the RGO closed in 1998. By 1979 the 4 m was on the verge