July 10: Alvan Graham Clark

Alvan Graham Clark

July 10, 1832 – June 9, 1897

Alvan Graham Clark was an American astronomer and telescope-maker. He was the son of Alvan Clark, founder of Alvan Clark & Sons.

Alvan Clark & Sons was an American maker of optics that became famous for crafting lenses for some of the largest refracting telescopes of the nineteenth and early twentieth centuries. Founded in 1846 in Cambridgeport, Massachusetts by Alvan Clark (1804–1887), a descendant of Cape Cod whalers who started as a portrait painter, and his sons George Bassett Clark (1827–1891) and Alvan Graham Clark. Five times, the firm built the largest refracting telescopes in the world.

On January 31, 1862, while testing a new 18 1/2 inch refracting telescope, he made the first observation of Sirius B in Cambridgeport, Massachusetts. The magnitude 8 companion of Sirius is also the first known white dwarf star.

The 18 1/2 inch refracting telescope is now still being used at the landmark Dearborn Observatory of Northwestern University in Evanston, IL.

For many years the Dearborn Telescope, the largest telescope in the world in its time, has been one of the most popular exhibits at the Adler Planetarium. The telescope has had an unusually varied career, and was recently sent out for a careful, professional facelift before resuming its place in the New Adler.