Around 1900 a group of (mostly women!) astronomers at Harvard came up with a classification scheme. Stars had been organized based on how strong their hydrogen lines were, but without physical understanding. Annie Jump Cannon was the first person to suggest a stellar classification scheme according to temperature.

AJC did most of the work that has become the basis for modern classification of stars. It was she who created this sequence: OBAFGKM, with the helpful mnemonic "Oh Be A Fine Girl/Guy, Kiss Me"

Left:Annie Jump Cannon. She helped create the modern stellar classification system. Right: Some of the stellar spectra she classified.

Historical note: Annie Jump Cannon is one of the first women to contribute to modern astronomy in such a significant way. She classified over 200,000 stellar spectra between 1911 and 1914. This catalog of objects is still used today by modern astronomers.

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