| William Herschel Telescope | |
 Moonrise over the William Herschel Telescope |
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| Organization: | Isaac Newton Group of Telescopes |
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| Location: | Roque de los Muchachos Observatory, La Palma, Canary Islands |
| Wavelength: | Optical / infrared |
| Built: | Completed June 1 1987 |
| Telescope style: | Cassegrain-Nasmyth Reflector |
| Diameter: | 4.2m |
| Collecting area: | 13.8m2 |
| Mounting: | Alt-azimuth |
| Website: | WHT Homepage |
The William Herschel Telescope or WHT was first conceived in the late 1960s, when the Anglo-Australian Observatory was being designed. The British astronomical community saw the need for telescopes of comparable power in the Northern Hemisphere. Planning began in 1974, but by 1979 the project was on the verge of being scrapped due to a ballooning budget. A re-design cut the price-tag substantially, and Dutch astronomers took a 20% stake in the project, allowing the project to be given the go-ahead in 1981. That year was the 200th anniversary of the discovery of Uranus by William Herschel, and it was decided to name the telescope in his honour. The telescope is a member of the Isaac Newton Group of Telescopes. Construction began in 1983, and the telescope was shipped to La Palma in 1985. It saw first light in 1987. The telescope has an altazimuth mount. The mirror is maintained so that its theoretical maximum resolution is less than 0.2 arcseconds. The typical seeing at La Palma is of the order of one arcsecond, so the telescope is limited by that. As a competitive research telescope, the WHT is heavily oversubscribed, and typically three times more applications for telescope time are received than can be accommodated. Notable discoveries made using the WHT include that of a hot bubble of expanding gas at the centre of our galaxy, suggestive of the presence of a supermassive black hole; the first observation of the optical counterpart of a gamma-ray burst; and recently, the discovery of a Wolf-Rayet star with the fastest-known stellar wind.
