Annie Jump Cannon compiled the first detailed catalog of the spectra of stars.
Annie Jump Cannon observed, classified, and analyzed 400,000 stars, carefully placing them in groups based on their spectra (or emission of radiation in waves). The best-known American woman astronomer of her time, she also gave lectures, wrote papers, and cataloged many variable stars. Although spectral classification was not new at the end of the 1890s, no one prior to Cannon had made a detailed survey of the stars according to their temperature and composition. Her method, which was adopted by the astronomical community in 1910, became known as the "Harvard system."
Mother influences early interest in astronomy
Annie Jump Cannon was born on December 11, 1863, in Dover, Delaware. She was the eldest of three children of Wilson Lee Cannon (who also had four children by a previous marriage), a shipbuilder, farm owner, and state senator, and his second wife, the former Mary Elizabeth Jump. Cannon's mother had been interested in astronomy since her own childhood, and together mother and daughter studied the sky from the attic of their house, where they had set up a simple observatory.
Cannon received her early education at local schools. In 1880, she graduated from the Wilmington Conference Academy (a Methodist institution), then continued her education at Wellesley College in Massachusetts. At Wellesley she studied with Sarah Frances Whiting, a professor of physics and astronomy. Cannon also delved into research on stellar spectroscopy, a process that breaks a star's light into component colors so that the various elements of the star can be observed.
Pursues interest in stellar spectroscopy
After earning a bachelor's degree at Wellesley in 1884, Cannon returned to her family home in Dover, where she lived for ten years. Continuing her involvement in astronomy, she visited Italy and Spain to observe a solar eclipse. She also became interested in photography. In 1894, following her mother's death, Cannon returned to Wellesley for postgraduate studies. There she worked as a teaching assistant in physics for Whiting and participated in experiments to confirm Wilhelm Röntgen's discovery of X rays. She soon turned to her attention to stellar spectroscopy, however, and in 1895 enrolled at Radcliffe College as a special student in astronomy.
Creates new system
The following year Cannon became an assistant at the Harvard College Observatory through the support of Edward Pickering, director of the observatory and a leader in the field of spectroscopy. She began a study of variable stars (stars whose light output varies because of internal fluctuations or because they are eclipsed by another star) and stellar spectra (the distinctive mix of radiation emitted by every star). She worked for a time at the Harvard astronomical station in Arequipa, Peru, which had been established by Pickering and his brother, William.
Using a method that combined the classification systems developed by American astronomers Antonia Maury and Williamina P. Fleming, Cannon classified 1,122 bright stars whose spectra had been photographed at Arequipa. Cannon's system arranged stars according to the color of the light they emit, which is determined by their temperature. She classified the hot, white or blue stars as types O, B, and A. Type F and G stars, like Earth's sun, are yellow; type K stars are orange; and type M, R, N, and S are reddish and therefore relatively cool. Known as the Harvard system, Cannon's method made possible the easy classification of all stars in relatively few, rationally related categories.
Catalogs stellar spectra
In 1911, the year after the Harvard system was adopted by other astronomers, Cannon was promoted to curator (superintendent) of astronomical photographs at the observatory. At this time she began one of the most extensive collections of astronomical data ever achieved by a single observer--the Henry Draper Catalogue of stellar spectra. Published by the Harvard College Observatory in ten volumes from 1918 to 1924, the catalog lists the spectral types of 225,300 stars, their positions in the sky, and their visual and photographic magnitudes; it also includes notes on the eccentricities of particular stars. As soon as Cannon finished this survey, she began enlarging the catalog to include fainter stars in the Milky Way, the Large Magellanic Cloud, and other selected regions of the cosmos. In all, Cannon classified the spectra of some 400,000 stars in her lifetime.
During the same period, Cannon pursued her interest in variable stars (stars whose brightness changes, usually in more or less regular periods). In 1903, she issued a catalog of the 1,227 variable stars known at the time. Four years later she published a second catalog of variable stars, presenting precise data and notes on two thousand stars. In the course of her work, she discovered three hundred previously unknown variables and five novae. (Novae are stars that suddenly increase in light output and then fade away within a few months or years.)
Achieves international reputation
Cannon was active in professional activities such as the annual meeting of astronomical societies. Astronomers from all over the world visited her at Star Cottage, her home in Cambridge, Massachusetts. She received a number of honorary degrees and awards, including election to the American Philosophical Society in 1925. Cannon was the first woman to be presented the Henry Draper Gold Medal of the National Academy of Sciences (NAS; 1931), the first woman granted an honorary doctoral degree from Oxford University in Cambridge, England, and the first woman elected to an office of the prestigious American Astronomical Society. In 1929, the National League of Woman Voters listed her as one of the twelve greatest living American women. She was later appointed William Cranch Bond Astronomer at Harvard University.
Cannon's achievements came at a time in the history of science when the roles for women in male-dominated disciplines were severely limited. Backward social attitudes and deep-seated gender prejudices blinded the scientific community to the outstanding contributions of women in the field. In 1923, two prominent members of the NAS discussed the possibility of electing Cannon to the ranks of the academy, an honor no woman had yet received. Despite the support of several distinguished fellow astronomers and Cannon's recognized contributions to science, she was not elected to the academy.
Cannon held her position at Harvard University until her retirement in 1940. She continued observing the stars until shortly before her death in Cambridge on April 13, 1941, at the age of seventy-seven.
- Lankford, John, and Rickey L. Slavings, "Gender and Science: Women in American Astronomy, 1859-1940," Physics Today, March 1990, pp. 58-65.
- Rossiter, Margaret W., Women Scientists in America: Struggles and Strategies to 1940, Johns Hopkins University Press, 1982.