US astronomer who
carried out revolutionary work on the classification of stars by examining
their spectra. Her system, still used today, has spectra arranged according
to temperature into categories labelled O, B, A, F, G, K, M, R, N, and
S. O-type stars are the hottest, with surface temperatures of over 25,000
Studying photographs, Cannon discovered 300 new variable stars. In 1901
she published a catalogue of the spectra of more than 1,000 stars, using
her new classification system. She went on to classify the spectra of
over 300,000 stars. Most of this work was published in a ten-volume
set which was completed 1924. It described almost all stars with magnitudes
greater than nine. Her later work included classification of the spectra
of fainter stars.
Cannon was born in Dover, Delaware, and studied at Wellesley and Radcliffe
colleges. She spent her career at the Harvard College Observatory, as
assistant 1896-1911, curator of astronomical photographs 1911-38, and
astronomer and curator 1938-40.
A system had been established 1890 for classifying stellar spectra into
categories labelled alphabetically A-Q. Cannon reformed this system.
Stars in the O, B, A group are white or blue, those in the F, G group
yellow, those in the K group orange, and those in the M, R, N, S group
red. Our Sun is yellow so its spectrum places it in the G group.