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a family of American opticians and amateur astronomers; including Alvan Clark (born Mar. 8, 1804, in Ashfield, Mass.; died Aug. 19, 1887, in Cambridge, Mass.) and his sons George (born in 1827; died in 1891) and Alvan Graham (born July 10, 1832, in Fall River, Mass.; died June 9, 1897, in Cambridge, Mass.).
The Clarks discovered many double stars, including the companion of Sirius. The Clarks’ largest refractors are in the U.S. Naval Observatory (refractor made in 1873; diameter of the objective, 66 cm), the Pulkovo Observatory (1885; diameter, 76 cm), the Lick Observatory (1888; diameter, 91 cm), and the Yerkes Observatory (1896; diameter, 102 cm).