Which astronomer classified more than 350,000 stars at Harvard Observatory?

Annie Jump Cannon classified more than 350,000 stars at Harvard Observatory.

Cannon developed and refined the Harvard spectral classification scheme, arranging stars by their spectral characteristics. The resulting sequence—O, B, A, F, G, K, M—remains a standard mnemonic for stellar classification. She could classify stars at an extraordinary rate, sometimes hundreds in an hour.

Her work used photographic plates collected by the Harvard College Observatory and was part of the larger effort known as the Harvard Computers. Cannon’s system was not simply a ranking of brightness; it reflected stellar temperature and spectral features.

She became curator of astronomical photographs at Harvard and received the Henry Draper Medal in 1931. The Sun belongs to spectral class G, specifically G2, while the hottest O-type stars appear blue and the coolest M-type stars appear red.