Alvan Graham Clark
Alvan Graham Clark 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 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 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 18.5 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.
