This Day in History – January 31st, 1862

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The arrow points to Sirius B, dwarfed by Sirius A.

A white dwarf, also called a degenerate dwarf, is a stellar remnant composed mostly of electron-degenerate matter. They are very dense; a white dwarf’s mass is comparable to that of the Sun, and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored thermal energy. The nearest known white dwarf is Sirius B, 8.6 light years away, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun. The unusual faintness of white dwarfs was first recognized in 1910 by Henry Norris Russell, Edward Charles Pickering, and Williamina Fleming; the name white dwarf was coined by Willem Luyten in 1922.

Alvan Graham ClarkSixty years prior to being labelled a “white dwarf,” Sirius B was discovered by Alvan Graham Clark, an American astronomer and telescope-maker. On January 31st, 1862, while testing a new 18½ 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 18½ inch refracting telescope is now still being used at the landmark Dearborn Observatory of Northwestern University in Evanston, Illinois.

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