Williamina Fleming

Henry Draper Catalogue, 1886

In 1886, Mary Anna Draper, the wealthy widow of astronomer Henry Draper, started the Henry Draper Memorial to fund the HCO's research.^[8][9] In response, the HCO began work on the first Henry Draper Catalogue, a long-term project to obtain the optical spectra of as many stars as possible and to index and classify stars by spectra.^[10]

Fleming was placed in charge of the Draper Catalogue project.^[7] A disagreement soon developed regarding classifying the stars.^[6] The analysis had been started by Nettie Farrar, but she left a few months later to be married. Antonia Maury advocated for a complex classification scheme. Fleming, however, wanted a much more simple, straightforward approach.^[11]

The latest Harvard College Observatory images contained photographed spectra of stars that extended into the ultraviolet range, which allowed much more accurate classifications than recording spectra by hand through an instrument at night.^[6] Fleming devised a system for classifying stars according to the relative amount of hydrogen observed in their spectra, known as the Pickering-Fleming system.^[12] Stars showing hydrogen as the most abundant element were classified A; those of hydrogen as the second-most abundant element, B; and so on.

Later, her colleague Annie Jump Cannon reordered the classification system based on the surface temperature of stars, resulting in the Harvard spectral classification, which is still in use today.^[13]

In 1890, the HCO published the first Henry Draper Catalogue due to years of work by their female computer team, a catalog with more than 10,000 stars classified according to their spectrum. Fleming did the majority of these classifications.^[14][when?] Fleming also made it possible to go back and compare recorded plates by organizing thousands of photographs by telescope along with other identifying factors.^[6] In 1898, she was appointed Curator of Astronomical Photographs at Harvard, the first woman to hold the position.^[12]

At the 1893 World's Fair in Chicago, Fleming openly advocated for other women in the sciences in her talk "A Field for Woman's Work in Astronomy", where she openly promoted hiring female assistants in astronomy. Her speech suggested she agreed with the prevailing idea that women were inferior but felt that, if given more significant opportunities, they would be able to become equals; in other words, the sex differences in this regard were more culturally constructed than biologically grounded.^[15]

Notable discoveries

During her career, Fleming discovered a total of 59 gaseous nebulae, over 310 variable stars, and 10 novae.^[5]

Most notably, in 1888, Fleming discovered the Horsehead Nebula on a telescope-photogrammetry plate made by astronomer W. H. Pickering, brother of E.C. Pickering. She described the bright nebula (later known as IC 434) as having "a semicircular indentation 5 minutes in diameter 30 minutes south of Zeta Orionis". Subsequent professional publications neglected to give credit to Fleming for the discovery. The first Dreyer Index Catalogue omitted Fleming's name from the list of contributors, having then discovered sky objects at Harvard, attributing the entire work merely to "Pickering". However, by the time the second Dreyer Index Catalogue was published in 1908, Fleming and her female colleagues at the HCO were sufficiently well-known and received proper credit for their discoveries.

Fleming is also credited with the discovery of the first white dwarf:

The first person who knew of the existence of white dwarfs was Mrs. Fleming; the next two, an hour or two later, Professor E. C. Pickering and I. With characteristic generosity, Pickering had volunteered to have the spectra of the stars which I had observed for parallax looked up on the Harvard plates. All those of faint absolute magnitude turned out to be of class G or later. Moved with curiosity I asked him about the companion of 40 Eridani. Characteristically, again, he telephoned to Mrs. Fleming who reported within an hour or so, that it was of Class A.

— Henry Norris Russell^[16]

In 1910, Fleming published her discovery of white dwarf stars .^[5] Her other notable publications include A Photographic Study of Variable Stars (1907), a list of 222 variable stars she had discovered; and Spectra and Photographic Magnitudes of Stars in Standard Regions (1911).

She became a US citizen in 1907.^[17]

She died of pneumonia in Boston on 21 May 1911,^[1][5][18] aged 54.