In the late 19th century, Harvard College Observatory was one of the world's top observatories. This was due to the vision, commitment and organizing skills of its director Edward Pickering. But his vision was realized through the hard work and dedication of a team of women assistants sometimes dismissively called Pickering's harem. One of the women was Williamina (Mina) Fleming, who began as a housekeeper and ended her career as an astronomer of international repute.

School, marriage, and a new life
Williamina Paton Stevens was born in Dundee, Scotland on May 15, 1857. She finished her schooling at fourteen and worked as a student teacher until she married widower James Fleming in 1877. The following year, the Flemings emigrated to America.

Unfortunately for Mina, but fortunately for astronomy, in 1879 she found herself in Boston, Massachusetts, pregnant and with her husband having left her. She got a job as a housekeeper to the Pickerings in Cambridge. Although Fleming had no higher education and wasn't trained in science, she was smart, observant and methodical, and Pickering offered her some work in the observatory. But first Fleming went back to Scotland where her son was born. When she returned to Cambridge, she left the baby with her mother. Her mother, son and a sister joined her six years later.

The Draper Memorial
In 1882 Henry Draper died. It would have a great effect on Harvard College Observatory, on Fleming's career and for women in astronomy. Henry Draper was a physician, but also a keen astrophotographer. He had begun photographing the spectra of stars in order to compile a catalog. In 1886 his widow Anna decided to donate the telescopes and a sum of money to Harvard Observatory if Pickering would complete the catalog as a memorial to her husband.

The computers
Astronomical photographs were on glass plates, which had to be indexed and cared for. Someone also had to identify the objects on them and compute their positions. Lacking electronic devices, the computers of those days were human. Traditionally, they had been men, but Pickering had other ideas. He felt that women could do the job, perhaps better than men. He was also pragmatic. Since women earned less than half what men did, with the available money he could hire twice as many.

The woman originally in charge of the Draper project resigned to get married, but before leaving she trained Fleming to take over. Not only had Fleming been a good worker and a good learner, but she also got very interested in astronomy. The existing system for classifying spectra was unsatisfactory, so Fleming devised a new one. She classified the spectra of over ten thousand stars and produced the Draper Catalogue of Stellar Spectra, published in 1890. Fleming wasn't named as an author, but Pickering gave her credit for her work.

Promotion and discoveries
In November 1898 Fleming was appointed to the position of Curator of Astronomical Photographs. Not only was she the first woman to hold this job, but it was also the first ever corporate appointment of a woman by Harvard College.

In the past, astronomers could only make discoveries by direct observation. With the advent of photography, discoveries could be made during office hours while studying glass plates. Fleming's best known discovery was the Horsehead Nebula, a dark cloud of dust in the constellation Orion. The header image to this article is a NASA image of the Horsehead Nebula.

Besides the work studying the plates and supervising the computers, Pickering had assigned her to work on proofs for publication. In her journal in March 1900 she wrote:

If one could go on and on with original work . . . life would be a most beautiful dream, but you come down to its realities when you have to put all that is most interesting to you aside, in order to use most of your available time preparing the work of others for publication.

Nonetheless over the years Fleming made numerous discoveries. Unusual stars known as Wolf-Rayet stars were first discovered in 1867, and in Fleming's time 107 were known. She discovered 94 of them. She also discovered over three hundred variable stars and ten novae. A nova is a star that shows a sudden dramatic increase in brightness and then fades away again. We now know that it's an explosion on the surface of a white dwarf star in a binary star system.

In 1907 she published A Photographic Study of Variable Stars, a study of 222 variable stars she had discovered. It included her selection of comparison stars that allowed the brightness of the variable stars to be accurately determined. Hers was the first photographic standard for determining stellar magnitude.

Memberships and honors
Fleming was a member of the Astronomical and Astrophysical Society of America (which later became the American Astronomical Society). She was made an Honorary Fellow in Astronomy of Wellesley College, and awarded the Guadalupe Almendaro medal by the Astronomical Society of Mexico. The Royal Astronomical Society of Great Britain awarded her honorary fellowship, which made Fleming one of six women to be so honored in the 85 years the society had existed.

Williamina Fleming died at the age of 54 on May 21, 1911 in Boston, Massachusetts.

English astronomer Herbert Hall Turner, who wrote her obituary for the Monthly Notices of the Royal Astronomical Society, said:

As an astronomer Mrs. Fleming was somewhat exceptional in being a woman; and in putting her work alongside that of others, it would be unjust not to remember that she left her heavy daily labours at the observatory to undertake on her return home those household cares of which a man usually expects to be relieved.