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Allegheny ObservatoryAn observatory sited in Riverview Park, in the city of Pittsburgh, Pennsylvania, USA, and operated by the Physics and Astronomy Department of the University of Pittsburgh. Founded in 1859, the observatory was taken over by the university in 1867 and was fully established on its present site by 1912. The observatory has three telescopes housed in three separate domes. The Fitz-Clark Refractor, a 33.02-centimeter instrument, was the observatory's original telescope, purchased in 1861; it has a focal length of 4.62 meters and a focal ratio of f/14. The William Thaw Memorial Refractor (aperture 76.2 cm, focal length 14.3 m, focal ratio f/18.8) was built in 1912 and designed for photographic work. In 1985 its object lens was upgraded to focus red light, a region of the spectrum in which the Pittsburgh skies are still relatively clear. The James E. Keeler Memorial Reflector (aperture 73.7 cm, focal length 4.56 m, focal ratio f/6) is the observatory's main instrument. Built in 1905 as a Cassegrain telescope, it was originally used for spectroscopy. In 1992 its mirrors were replaced with ones made from a Russian version of Cer-Vit and its optics were upgraded to an f/15 Ritchey–Chrétien system (see Ritchey–Chrétien optics). Among the observatory's other instruments is a nulti-channel astrometric photometer (MAP), designed by George A. Gatewood, the institution's director from 1977. The Allegheny Observatory is today a world leader in high-precision astrometry. Its measurements are being used most significantly in the search for extrasolar planetary systems.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006