Alvan Graham Clark (July 10, 1832 – June 9, 1897), born in Fall River, Massachusetts, was an American astronomer and telescope-maker. He was the son of Alvan Clark. In 1862, while testing Northwestern University's Dearborn Telescope in Evanston, Illinois, which was a new 18-inch refracting telescope, he discovered Sirius B, the magnitude 8 companion of Sirius and the first known white dwarf.