One astronomer hand-classified about 400,000 stars by their light alone

Annie Jump Cannon, working at Harvard as one of the 'Pickering's Women' human computers, simplified a tangle of competing star-classification schemes into the OBAFGKM sequence still taught today, ordered by temperature. Working mostly from photographic spectra rather than a telescope eyepiece, she personally classified nearly 400,000 stars, and the system she built was adopted internationally in 1922.

— Annie Jump Cannon, Annie Jump Cannon — Henry Draper Catalogue, Harvard College Observatory