Cannon , Annie Jump

(1863–1941) American astronomer

Annie Cannon was the daughter of a Delaware state senator and was born in Dover in that state. She was one of the first girls from Delaware to attend university, being a student at Wellesley College from 1880 to 1884. After a decade spent at home, where she became deaf through scarlet fever, she entered Radcliffe College in 1895 to study astronomy. In 1896 she was appointed to the staff of the Harvard College Observatory, as it was the practice of the observatory, under the directorship of Edward Pickering, to employ young well-educated women to do calculations. She worked there for the rest of her career, serving from 1911 to 1932 as curator of astronomical photographs. In 1938, after nearly half a century of distinguished service, she was appointed William Cranch Bond Astronomer.

One of the main programs of the observatory was the preparation of the Henry Draper Catalogue of a quarter of a million stellar spectra. Stars were originally to be classified into one of the 17 spectral types, A to Q, which were ordered alphabetically in terms of the intensity of the hydrogen absorption lines. Cannon saw that a more natural order could be achieved if some classes were omitted, others added, and the total reordered in terms of decreasing surface temperature. This produced the sequence O, B, A, F, G, K, M, R, N, and S. Cannon showed that the great majority of stars can be placed in one of the groups between O and M. Her classification scheme has since only been slightly altered.

Cannon developed a phenomenal skill in cataloging stars and at the height of her power it was claimed that she could classify three stars a minute. Her classification of over 225,000 stars, brighter than 9th or 10th magnitude, and the compilation of theCatalogue took many years. It was finally published, between 1918 and 1924, as volumes 91 to 99 of the Annals of Harvard College Observatory. She continued the work unabated, later publications including an additional 47,000 classifications in theHenry Draper Extension ( Annals, vol. 100, 1925–36). Even as late as 1936 when she was over 70 she undertook the classification of 10,000 faint stars submitted to her by the Cape of Good Hope Observatory.