Harvard College Observatory was founded in 1839. Astronomy was just beginning to be taught as a science in its own right, instead of as an extension of philosophy. Universities were beginning to receive funds for astronomical research, and data was beginning to accumulate faster than it could be analyzed. In 1877 Edward Charles Pickering became the director of the observatory, and it is he who is responsible for opening the doors of astronomy to women.
Although women had been volunteers at the observatory in the past, usually relatives of men on Harvard’s payroll, Pickering convinced the Harvard Corporation to hire women for the tedious work of computing. The women computers at Harvard College Observatory became known as “Pickering’s Harem”. He paid them half what men were paid to do this work, so he was able to afford twice as many workers. This proved to be important because Harvard was about to take on the monumental task of photographing and cataloging the entire sky; the Henry Draper catalog.
Henry Draper, was a wealthy physician, an amateur astronomer, and a pioneer in the field of astrophotography. He recorded the first stellar spectrum, which he took of Vega in 1872. He took the first photograph of an astronomical nebula, recording the Great Orion Nebula in 1880. He obtained the first wide-angle photograph of a comet’s tail, and the first spectrum of a comet’s head in 1881. Draper invented the slit spectrograph and pushed the state of the art in photography, optics, and telescope clock drives.
His great ambition was to photograph the entire night sky, to create a complete spectral catalog that would be available for astronomical research. He did not realize his dream due to his untimely death at the age of 45. His widow, Anna Mary Palmer, did not let his dream die. She donated money to the Harvard College Observatory to complete this monumental task in honor of her husband.
Williamina Fleming was born in Scotland in 1857. Mina, as her friends and family called her, attended public schools, where at the young age of 14, she began student teaching. Her teaching career lasted six years until 1877, when she married James Orr Fleming. The young couple sailed to America in December 1878 and took up residence in Boston, Massachusetts. A few months later, James abandoned his wife, and his unborn child.
Fleming found herself in a strange country, alone, pregnant, and in need of money to support herself. She found employment as a housekeeper. Her new employer was Edward Charles Pickering, the director of Harvard College Observatory.
Not long after Fleming began working in Pickering’s household, he offered her a position at the observatory. One story abut how this came to be is that Pickering, unsatisfied with the work of a male assistant at the observatory, complained that his housekeeper could do better work. She did do a better job than his previous assistant and in 1881, she became a permanent member of the observatory staff.
Five years later, in 1886, the Harvard College Observatory received funding from Anna Draper to compile her husband’s catalog project. Williamina was responsible for cataloging, indexing, examination, and care of the new photographic plates. The “computers” were responsible for identifying the stars on the plates and then calculating their positions. Twelve years later, the Harvard corporation officially recognized Fleming’s position. In 1898 she was bestowed the title of Curator of Astronomical Photographs, becoming the first woman to receive an appointment of this kind.
It was also her responsibility to catalog the plates so they would be accessible and the data readily available. She devised her own spectral classification system, after discounting the system devised by Father Angelo Secchi as too simplistic to account for the wide variety of stellar spectra. Fleming’s system divided the stars into classes, from A to Q, and was based on the complexity of the spectrum lines and bands and the strength of the spectral lines due to hydrogen. Stars that did not fall neatly within a category were grouped into Q.
In 1890, the first Henry Draper Catalogue was published in the Annals of the Harvard College Observatory. It contained most of the stars visible to the unaided eye, a total of 10,351 stars. Though Fleming was not listed as an author, Pickering did acknowledge her contribution to the work. She was also widely recognized by the astronomical community.
During Fleming’s tenure at Harvard, she discovered many celestial objects, including 10 novae, 94 Wolf-Rayet stars, and 222 long-period variables. She also received many honors and awards, including memberships in the Royal Astronomical Society and the Astronomical Society of Mexico.
Fleming worked at Harvard College Observatory until her death at age 54 in 1911.
Maury was hired by Pickering in 1888. She was responsible for cataloging stellar spectra for stars in the northern hemisphere. Maury, however, had an interest in theoretical work, something Pickering discouraged in his computers. This strained the relationship between Maury and Pickering, resulting in her intermittent employment during her years at Harvard College Observatory. Dorrit Hoffleit, one of Maury’s colleagues at Harvard College Observatory wrote, “She was one of the most original thinkers of all the women Pickering employed; but instead of encouraging her attempts at interpreting observations, he was only irritated by her independence and departure from assigned and expected routine.”
Maury rearranged Fleming’s spectral scheme to reflect the temperatures of stars. She further refined the sequence by adding another dimension to describe the spectral lines using small case letters. Maury firmly believed that the ‘c-characteristic’ in her system represented a fundamental property of the stars. Other astronomers agreed. In 1905, famed Danish astronomer Ejnar Hertzsprung published his work on stellar magnitudes and luminosities. His “red giant” objects turned out to be the same stars Maury had cataloged with the ‘c-characteristic.’ According to Hertzsprung the separation of the c- and ac- stars by Antonia Maury was the most important advancement in stellar classification since Secchi.
Maury did not complete her work at Harvard College Observatory, leaving in 1891 to pursue a position at Gilman School in Cambridge, Massachusetts. She returned in 1893 for one year, and again in December 1895 to assist with the final phase in the Draper project. The Henry Draper Catalogue was finally published in 1897.
After the completion of the catalogue, Maury lectured on astronomy to professionals in the field, as well as the public. She co-discovered the first spectroscopic binaries, Mizar in Ursa Major, and Beta Aurigae, and was also the first to calculate their orbits. The famous astronomer, John Herschel called her work on spectroscopic binaries “one of the most notable advances in physical astronomy ever made.”
Maury retired from Harvard College Observatory in 1935. She continued to visit Harvard College Observatory to check on observations of her final project, the enigmatic star, Beta Lyrae, until her death in 1952.
Three years after graduation, she became a volunteer research assistant at Harvard College Observatory. Seven years later, in 1902, Pickering hired her on the permanent staff at $.30 per hour. She was given the position of chief of the photographic photometry department and was responsible for the care of telescopes. Leavitt worked sporadically during her time at Harvard, often sidelined by health problems and family obligations. An illness contracted after her graduation from Radcliffe rendered her increasingly deaf.
Leavitt performed research from the observatory’s photographic plate collection. Using these plates, she was charged with determining the brightness of stars in the images. There was no existing standard for ascertaining stellar magnitudes at the time, so Leavitt devised her own system, called “the north polar sequence”. Recognized by the scientific community as an important standard, it was adopted by the International Committee on Photographic Magnitudes in 1913.
Another area of research that Leavitt pursued was variable stars. During her lifetime, she discovered over 1,200 variable stars, half the number of all known variables at the time of her death. In 1908, she made her most important discovery while studying Cepheid variables in the Magellanic Clouds. Leavitt determined that there is a relationship between a Cepheid variable's luminosity and its pulsation period. This period-luminosity relationship is very precise, making Cepheids important standard candles and the foundation of the Cosmological Distance Scale.
Leavitt was a member of Phi Beta Kappa, the American Association of University Women, the American Astronomical and Astrophysical Society, the American Association for the Advancement of Science, and an honorary member of the American Association of Variable Star Observers.
She died on December 21, 1921 from cancer.
For the next eleven years, Cannon studied music and traveled. It was during this time, after a bout of scarlet fever, that she lost her hearing. Upon the death of her mother, she decided to pursue her interests in astronomy full time and went to Radcliffe College as a “special student” for two years. Edwin Pickering was instrumental in her obtaining this special status. In 1896, she joined the ranks of computers at Harvard College Observatory.
Cannon’s duties included cataloging variable stars and classifying the spectra of stars in the southern hemisphere for the Henry Draper Catalogue project, the counterpart to Maury with the northern hemisphere. In her free time, Cannon poured over the observatory’s photographic plate collection, studying variable stars.
Cannon was recognized as the leading expert in identifying and classifying stars, with incredible accuracy and speed. By the time of her death, she had classified up to 350,000 stars, at a rate of up to 300 per hour.
Cannon refined the spectral classification schemes of her predecessors, Fleming and Maury. She reduced the number of categories and arranged them by temperature, from high to low, leaving us with the familiar OBAFGKM. Cannon used numbers from 1-10 to reflect gradation within each category. Her category scheme was so “user-friendly,” it was officially adopted as the standard in 1910 by the International Astronomical Union. Today, with only minor changes, Cannon’s system is known as the Harvard Spectral Classification.
She took over the duties as Curator of Astronomical Photographs when Fleming died in 1911. Cannon also published several volumes of catalogs, including her “Provisional Catalogue” in 1903, with a revision in 1907 listing 1,957 variable stars and their discoverers, the most complete list of its kind at the time. She also revised the Henry Draper Catalogue down to 8th magnitude, published in sections between 1918 and 1924.
Cannon received six honorary degrees, one from Oxford University, the first given to a woman, and was the first woman to receive the Draper Gold Medal. She also established an award to recognize contributions to astronomy by women. She is one of the founding charter members of the American Association of Variable Star Observers.
Cannon worked at Harvard College Observatory for 45 years, until her death at age 77.