In the early 1920s, the astronomy community was divided. A centuries-old question — whether ours was the only galaxy, or if there were others — still had no definitive answer.
Some argued that all the stars and clouds of dust and gas seen in the night sky were a part of the Milky Way. Others believed that some of those dusty, gaseous formations — called spiral nebulae — were, in fact, other galaxies. That, despite their hazy appearance, there were stars within spiral nebulae. They were just too far away to be seen clearly with the telescopes of the time.
Learn more about this center for astronomy in Southern California on "Lost LA" S4 E5: Discovering the Universe - Exploring the Cosmos Atop Mount Wilson.
Indeed, the latter hypothesis turned out to be true, as Edwin Hubble demonstrated at Mount Wilson Observatory in 1923. There are other galaxies beyond our own. We would never know this, if not for a type of pulsating star called the Cepheid variable. At a time when women astronomers were few and most often relegated to working as assistants, it was one such assistant who made a crucial and fundamental discovery about the nature of Cepheid variables. In doing so, Henrietta Swan Leavitt provided the key to solving one of the most significant celestial uncertainties of her time.
Henrietta Swan Leavitt was born on July 4, 1868, in Lancaster, Mass. She was the eldest daughter of George Roswell Leavitt — a minister — and his wife, also named Henrietta Swan. “Miss Leavitt inherited, in a somewhat chastened form, the stern values of her puritan ancestors. She took life seriously,” wrote her colleague, Solon.I. Bailey, upon her death. "Her sense of duty, justice and loyalty were strong." He describes her as being religious, devoted to her family and a considerate friend. "She had the happy faculty of appreciating all that was worthy and lovable in others and was possessed of a nature so full of sunshine that all of life became beautiful and full of meaning," Bailey added.
In 1888, at the age of 20, she enrolled in Radcliffe College (known then as the Society for the Collegiate Instruction of Women and nicknamed the “Harvard Annex”). There were not many science courses offered there at the time, Leavitt’s biographer, George Johnson, notes. She took physics, analytical geometry and differential calculus. And in her fourth year, she took a course in astronomy, earning an A. But, we do not know what drew her to the subject and led her to make it her life’s work. “No diary has been found recording what it was about the stars that moved her,” Johnson writes. “One of history’s small players, her story has been allowed to slip through the cracks.”
Leavitt completed her studies in 1892. A man finishing the very same course of study would have earned a B.A, but Leavitt came away with only a certificate.
The ComputerShortly after that, Leavitt began working at the Harvard College Observatory (HCO), first as a volunteer (1894-96) and then as a full-time employee (in 1902). She was one of a corps of women assistants known as “computers.” Her job was to study a vast number of photographs of the night sky and gather data about the nature of the stars.
Leavitt's position was relatively novel for the time. The director of the observatory, Edward Charles Pickering, had recently begun using photographic technology to capture images of stars as seen through a telescope. The resulting images of tens of thousands of stars brought about the need for several tenacious and precise minds to sift through multitudes of data.
According to science historian Margaret W. Rossiter, Pickering was an advocate for the higher education of women and thought that they might fit the bill exactly. His first hire was his housekeeper, Williamina Fleming. Pleased with Fleming's work, Pickering tasked her with hiring more women assistants. Between 1885 and 1900, Fleming had twenty assistants, including Leavitt. These "computers" were also rather irreverently referred to as "Pickering's Harem."
The practice of hiring women computers became popular in other observatories in the country as well. Rossiter notes that between 1875 and 1920, 164 women worked in observatories for at least a year or more; 12 at Mount Wilson. They were mostly high school graduates, though college graduates were well sought after.
These women were essential to the success of research endeavors. Harlow Shapley, who worked at Mount Wilson Observatory before taking over at HCO in 1921 following Pickering’s death, used the term “girl-hours” to describe the time it took to work on a research problem. “I introduced the term “girl hours,” and it would take a lot of girl hours to solve some of the problems. In fact, one job took several kilo-girl hours to get it through. So I should say that I had help on a lot of the details,” he said. He also noted that while there were only a few assistants at Mount Wilson Observatory, HCO was “swarming with these assistants.” “That’s why we got somewhere, got it done,” he added.
Click right or left to see some of the correspondence between Mt. Wilson and the computers it sought to hire:
August 2, 1920
Miss Charlotte Abbott,
5 Providence Road,
Charlotte, North Carolina
Dear Miss Abbott:
We wish to find someone to fill a vacancy here as soon as possible. If later you find yourself free, I should be glad to hear from you, for we may have something that you could do.
Yours very truly,
Superintendent Computing Division
August 24, 1920
Mr. F.H. Seares,
Mount Wilson Solar Observatory
Dear Mr. Seares,
I have your letter of August second and have given much thought to the matter. Please tell me whether conditions there are such that the salary you offer would be a living wage, and whether I could be immediately useful in the observatory or would need training. Would we live on the mountain or in Pasadena?
I may be able to accept a position in January but not before.
Very truly yours,
Charlotte Bushnell Abbott
Vassar College, Poughkeepsie, New York
Mr. F.H Seares
Mount Wilson Solar Observatory
My dear Mr. Seares,
Miss Sheldon of your staff writes me that there is to be a vacancy on the staff of computers in the near future. I am very anxious to come to California for work that is not teaching – after my graduation in June. Do you think it would be possible that I might be able to fill the vacancy? I have had the following courses in mathematics:
- Solid and spherical geometry
- Algebra and plane trigonometry
- Analytic geometry
- Advanced algebra
- Elementary differential and integral calculus
- Theory of equations
- Curve tracing
I am taking a course on general astronomy with Miss Furness next semester, which consists of a mathematical treatment of the principal branches of astronomy. Miss Sheldon is a very dear friend of mine and has assured me that I would be much interested in the work of the observatory — and also much pleased with Pasadena itself.
For further reference, please apply to Ella [not legible], Secretary of Vassar College, [not legible] Professor of Mathematics, Vassar College, and Miss Eleanor Furness, with whom I shall be studying after February the fifth. If it is necessary, I am willing to do some summer school work in both astronomy and mathematics, allowing me to reach Pasadena in September.
Ruth E. Barnett
January 13, 1912
Many of the assistants were considered noted astronomers even at the time. Some, including Fleming, was even listed in editions of "American Men in Science." Margaret Harwood, who started her career at HCO, went on to become the director of the Maria Mitchell Observatory in Nantucket. Yet,