Williamina Paton Stevens Fleming

Astronomer

  • Born: May 15, 1857
  • Birthplace: Dundee, Scotland
  • Died: May 21, 1911
  • Place of death: Boston, Massachusetts

Scottish-born American astronomer

Fleming pioneered the analysis of stellar spectra and discovered more than three hundred variable stars and ten exploding stars (novas). Her work made her the leading woman astronomer of her time.

Area of achievement Astronomy

Early Life

Williamina Paton Stevens Fleming was born in Scotland to Robert Stevens and Mary Walker Stevens. Her father was a craftsperson in the carving and gilding trade and was among the first in Dundee, Scotland, to experiment with the new daguerreotype photographic process. He died when Williamina was seven.

Williamina became a pupil-teacher at the age of fourteen. In 1877, after five years of teaching, she married James Orr Fleming; the following year they emigrated to the United States and settled in Boston. After her husband abandoned her two years later, she took a job as a maid in the home of Edward C. Pickering, who was director of the Harvard College Observatory from 1877 to 1919. A few months later she took a short leave to return to Scotland for the birth of her son, Edward Pickering Fleming, who would later graduate from the Massachusetts Institute of Technology and become a mining engineer and metallurgist.

At the Harvard College Observatory, Pickering pioneered in employing women as “computers”—people who measured and analyzed the vast number of stellar-spectrum photographs he was producing. At that time, women were not allowed to work in the observatory at night, when observations of the skies were made, but they could be employed during the daytime to analyze photographs at salaries that were lower than those of male astronomers. When Pickering became impatient with the inefficiency of a male assistant, he claimed that his Scottish maid could do a better job. In 1881, he invited Fleming to work as a computer at Harvard, even though she had neither a college education nor training in astronomy. However, her work was so good that Pickering decided to hire other young women to work with her. Over the next thirty years, Fleming worked closely with Pickering, first in clerical and computing work, but advancing rapidly to become one of the leading astronomers of her day and to supervise many other women computers at Harvard.

Life’s Work

During the nineteenth century astronomy underwent a major revolution. New techniques for lens making, more advanced telescope designs, and the use of photography led to measurements of fainter stars with greater precision than ever before. In 1872, the American physician Henry Draper made the first successful photograph of the spectrum of a star. After Draper died in 1882, his widow established the Henry Draper Memorial to assist the program of stellar spectroscopy at the Harvard College Observatory. When a thin prism was placed in front of the objective lens of a refracting telescope, each star formed its own spectrum on a photographic plate at the focus, making it possible to record long exposures of spectra of as many as two hundred stars on a single photographic plate. In 1886, Fleming was placed in charge of the Draper project to measure, analyze, and classify stellar spectra.

Fleming’s chief assignment was classifying stars on the basis of the various patterns of lines and bands that appeared in their spectral photographs. Because photographs were more sensitive than the human eye, they revealed new features that required a more complex classification scheme than earlier systems based solely on visual observations. In the “Pickering-Fleming system” light spectra were organized into fifteen categories, using most of the letters from A to Q according to the complexity of their lines and bands, but about 99 percent of the stars were in the six classes designated A, B, F, G, K, and M.

In 1890, the Draper Catalogue of Stellar Spectra was published as volume 27 of the Annals of Harvard College Observatory. Fleming’s earlier work had been published in the customary way under the name of the director of the observatory. However, by the year 1890, the signature “M. Fleming” began to appear along with Pickering’s on reports in astronomy journals. In the Draper Catalogue, Pickering acknowledged that “Mrs. M. Fleming” did most of the work in measuring and classifying spectra and preparing the catalog for publication. In the preparation of the catalog, Fleming used 633 photographic plates taken with the eight-inch Bache telescope. She measured 28,266 spectra and classified 10,351 stars brighter than seventh magnitude.

In the course of her work on the Draper Catalogue, Fleming found that the spectra of many variable red stars contained bright emission lines in addition to the usual dark absorption lines. Her further investigation showed that all stars with such unusual spectral features are variable in their luminosity. Her finding provided a new tool for discovering long-period variables. Using this technique, she discovered 222 variable stars. In her 1907 paper “A Photographic Study of Variable Stars,” which was published as volume 47 of the Annals of Harvard College Observatory, she gave the variation in brightness of each star based on a selected list of companion stars.

In addition to Fleming’s work on variable stars, she made a special study of other stars with peculiar spectra. This led her to the discovery of ten novas—or exploding stars—more than a third of the twenty-eight novas known at the time of her death. She also discovered 94 of the 107 known Wolf-Rayet stars, which are massive stars characterized by broad emission lines. Shortly after she died, her list of “Stars Having Peculiar Spectra” was published as volume 56 of the Annals of Harvard College Observatory in 1912.

Fleming combined her diligence and research ability with effective administrative skill in her supervision of several dozen young women. She also served as editor of all the publications issued by the Harvard College Observatory. In 1898, the Harvard Corporation named her curator of astronomical photographs. Under her supervision, nearly 200,000 photographic plates taken at Cambridge and in Peru between 1882 and 1910 were examined and cataloged. In 1906, she became the first American woman elected to the British Royal Astronomical Society, and she was also a charter member of the American Astronomical and Astrophysical Society. In 1911 she became ill with pneumonia and died in Boston at the age of fifty-four.

Significance

Williamina Fleming’s discovery and analysis of 222 variable stars and ten novas was unprecedented. The unusual nature of this achievement can be better appreciated when it is understood that most astronomers were proud to discover even one variable star and that they then typically left the further study of its properties to others. Fleming’s influence on the many assistants who worked under her was even more significant. Her pioneering classification scheme led to major contributions by other women who followed her example at Harvard. Two of the most important of these were Annie Jump Cannon and Henrietta Leavitt, both of whom began as her assistants.

Annie Cannon joined the Harvard staff in 1896 and developed the definitive Harvard system of spectral classification based on the work of Fleming. She organized Fleming’s alphabetical system according to increasing spectral complexity, and her system led to a later correlation with decreasing temperatures and an understanding of the evolution of stars. Henrietta Leavitt continued Fleming’s study of variable stars and became a full staff member in 1902. Ten years later, she announced her discovery of the relation between the pulsation period and luminosity of a type of variable star called Cepheids that later led to measurements of the distances of galaxies and the discovery of the expansion of the universe.

Bibliography

Belkora, Leila. Minding the Heavens: The Story of Our Discovery of the Milky Way. Bristol, England: Institute of Physics, 2003. Fleming is briefly discussed in a chapter on William Huggins and astronomical spectroscopy.

Cannon, Annie J. “Williamina Paton Fleming.” Astrophysical Journal 34 (July, 1911): 314-317. Obituary of Fleming written by one of her colleagues at the Harvard College Observatory.

Dobson, Andrea K., and Katherine Bracher. “Urania’s Heritage: A Historical Introduction to Women in Astronomy.” Mercury: The Journal of the Astronomical Society of the Pacific 21 (January/February, 1992): 4-15. This well-illustrated article includes a discussion of the work of Fleming and Cannon.

Jones, Bessie, and Lyle Boyd. The Harvard College Observatory, 1839-1919. Cambridge, Mass.: Harvard University Press, 1971. Several sections of this history discuss Fleming’s work and contributions.

Kass-Simons, G., and Patricia Farnes, eds. Women of Science: Righting the Record. Bloomington: Indiana University Press, 1990. A chapter on “Women in Astronomy in America” has a good discussion of the Harvard College Observatory women.

Spradley, Joseph L. “The Industrious Mrs. Fleming.” Astronomy 18 (July, 1990): 48-51. A short account of Fleming’s life and work with several photographs of her and others of the Harvard College Observatory women.

January 1, 1801: First Asteroid Is Discovered; 1814: Fraunhofer Invents the Spectroscope.