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Cannon, Annie Jump

stars classification spectra catalogue

(1863–1941) US astronomer: compiled Henry Draper catalogue of variable stars.

Originally interested in astronomy by her mother, Annie Cannon graduated from Wellesley College in 1884. For the next 10 years she lived at home but after the death of her mother she returned to study physics at Wellesley, and specialized in astronomy at Radcliffe College. In 1896 she was appointed by E C Pickering (1846–1919) to the staff at Harvard College Observatory where she began the study of variable stars and stellar spectra. These spectra were studied by Pickering’s objective prism method, which made spectra visible even from faint (9th or 10th magnitude) stars. Colour film was not available and classification by eye was a skilled task.

Her first major publication (1901) was a catalogue of 1122 southern stars which built upon the early classification used by Williamina Fleming (1857–1911). Annie Cannon’s system represented a sequence of continuous change from the very hot white and blue stars of types O and B, which showed many helium lines, through the less hot stars of types A, F, G and K to the very red stars of type M, which were cool enough that compounds of chemical elements, such as titanium and carbon oxides, could exist in their atmospheres. However, it was not then known that it was a temperature sequence. In 1910 Annie Cannon’s scheme was adopted as the official classification system at all observatories.

Her most important work was the Henry Draper Catalogue of Stellar Spectra , published by the Harvard Observatory between 1918 and 1924, which lists the spectral types and magnitudes of 225 300 stars, all those brighter than ninth magnitude, giving their positions and visual and photographic magnitude. In 1922 the classification system used by her in the catalogue was adopted by the International Astronomical Union as the official system for the classification for stellar spectra. She then began on an extension to fainter stars, in selected regions of the sky, down to about the 11th magnitude, and was occupied with this task until her death. She discovered 277 variable stars and five novae.

Annie Cannon received many academic honours; she received honorary degrees from four universities, including Oxford, where she was the first woman to be honoured with a doctor’s degree (1925).

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