Alvan Graham Clark

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Alvan Graham Clark
Yerkes Observatory Astro4p6.jpg
Alvan Clark and his assistant Carl Lundin (right) alongside the 40-inch lens, 1896
Born (1832-07-10)July 10, 1832
Fall River, Massachusetts
Died June 9, 1897(1897-06-09) (aged 65)
Nationality American
Fields Astronomy
Known for Sirius B

Alvan Graham Clark (July 10, 1832 – June 9, 1897) was an American astronomer and telescope-maker.

Born in Fall River, Massachusetts, he was the son of Alvan Clark, founder of Alvan Clark & Sons.

On January 31, 1862, while testing a new 18.5-inch (470 mm) aperture great refractor telescope in Cambridgeport, Massachusetts, Clark made the first ever observation of a white dwarf star. This discovery of Sirius B, or affectionately "the Pup", proved an earlier hypotheses (Friedrich Bessel in 1844) that Sirius, the brightest star in the night sky with an apparent magnitude of −1.46, had an unseen companion disturbing its motion. Clark used the largest refracting telescope lens in existence at the time, and the largest telescope in the United States, to observe the magnitude 8 companion.

Clark's 18½ inch refracting telescope was then delivered to his customer, the landmark Dearborn Observatory of Northwestern University in Evanston, Illinois, where it is still being used today.[1]

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