Cecilia Payne, ca. 1930s

Cecilia Payne-Gaposchkin, seen at her desk at Harvard College Observatory. Unknown photographer, unknown year. Smithsonian Institution Archives.

Cecilia Payne-Gaposchkin (1900—1979) was a British-born American astronomer who discovered that stars are made mainly of hydrogen and helium and established that stars could be classified according to their temperatures.

Payne entered the University of Cambridge in 1919, but she felt there were more opportunities for a woman to work in astronomy in the United States than in Britain. In 1923 she received a fellowship to study at the Harvard College Observatory in Cambridge, Mass.

Beginning in the 1880s, astronomers at Harvard College such as Edward Pickering, Annie Jump Cannon, Williamina Fleming, and Antonia Maury had succeeded in classifying stars according to their spectra into seven types: O, B, A, F, G, K, and M. It was believed that this sequence corresponded to the surface temperature of the stars, with O being the hottest and M the coolest. In her Ph.D. thesis (published as Stellar Atmospheres [1925]), Payne used the spectral lines of many different elements and the work of Indian astrophysicist Meghnad Saha, who had discovered an equation relating the ionization states of an element in a star to the temperature to definitively establish that the spectral sequence did correspond to quantifiable stellar temperatures. Payne also determined that stars are composed mostly of hydrogen and helium. However, she was dissuaded from this conclusion by astronomer Henry Norris Russell, who thought that stars would have the same composition as Earth. (Russell conceded in 1929 that Payne was correct.)

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