IT IS New Year’s Eve 1929, and the staff of the Harvard University Observatory are enjoying an evening of musical theatre: the show is called Observatory Pinafore (very loosely based on H.M.S. Pinafore). At first sight you might think that the women on the stage are the wives and daughters of the observatory staff. You would be wrong.
Though largely untrained, and paid a pittance to do drudge work for the male astronomers, these women were remarkable researchers. They and their predecessors at the observatory made significant contributions to science. Anyone who has studied astronomy, for example, has used Annie Jump Cannon’s stellar classification system. And the very foundations of cosmology came about through work performed at Harvard by one Henrietta Leavitt. When Edward Pickering, the observatory director, first recruited these novices – in a gesture of exasperation – he could never have imagined the consequences.
Their story began in 1877, when Pickering became director of the Harvard College Observatory. The observatory’s relentless programme of photographing and cataloguing all the objects in the night sky meant that Harvard astronomers were producing mountains of raw data – they would expose half a million photographic plates in the decades to come. Pickering readied the observatory for the task by establishing an industrial-scale workforce of people known as “computers” (only later did this term gain its modern sense) to carry out the analysis.
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Initially the computers were all young men. However, Pickering soon became frustrated at their poor attention to detail, and one day, when his patience had been exhausted, he blurted out that his Scottish maid could do a better job. He sacked his team and hired around a dozen women to do the job. It wasn’t an entirely selfless, liberal act. As Pickering suspected, the women were more meticulous than the men, but they also accepted half the salary that the men had demanded.
Pickering did indeed put his maid in charge. Williamina Fleming had been a teacher in Scotland before emigrating to America, where her husband abandoned her when pregnant, forcing her to take a job as a housekeeper. Now this single mother from Dundee was leading a team charged with scrutinising the world’s largest set of astronomical images.
They weren’t, of course, allowed to touch the telescopes. For a start, it was considered unsuitable for the fairer sex to work through the long, cold nights. But Victorian sensitivities would also have been offended by the thought of a man and a woman staring up at the stars together. However, it was not long before the computers were drawing their own insightful scientific conclusions.
Endless days spent staring at the photographic plates gave the women an intimate familiarity with the night sky and led to numerous discoveries. Fleming, for example, would find 10 of the 24 flaring nova stars then known. And Annie Jump Cannon catalogued roughly 5000 stars per month between 1911 and 1915, calculating the location, brightness and colour of each one. She made a major contribution to the system of stellar classification, establishing a system that, with only minor modifications, is still in use.
Some have suggested that Cannon’s keen eye was the legacy of a bout of scarlet fever: the illness left her almost completely deaf, and she may well have compensated by sharpening her attention to visual detail. She was certainly adept at picking up things that had been missed by others, and the idea is reinforced by the fact that the most famous member of the team, Henrietta Leavitt, was also deaf.
When Leavitt became a computer at the Harvard College Observatory in 1895, she grew interested in sifting through the plates and searching for stars whose brightness changed over time. Photography had transformed the study of these “variable stars”, because two glass plates taken on different nights could be overlaid and directly compared, making it much easier to spot any differences. Leavitt went on to discover around half of the variable stars known in her day. Professor Charles Young of Princeton University was so impressed that he called her “a variable star fiend”.
“Hubble used Leavitt’s work to provide the first evidence for the big bang model of the universe”
And Leavitt did more than catalogue the variable stars. She focused her efforts on a group of them known as cepheids, and showed that each cepheid’s rate of variation was directly correlated with its absolute brightness. A cepheid that takes a couple of weeks to fade and brighten again, for example, has a greater absolute brightness than one that fades and brightens over the course of just a few nights.
It was a significant discovery, and it would provide astronomers with their first means of measuring the distances to the stars. If a cepheid’s rate of variation betrayed its absolute brightness, then this could be compared with its apparent brightness to deduce its distance. In due course, astronomers mapped the heavens using Leavitt’s yardstick. Indeed, Edwin Hubble used cepheids to measure the distances to the galaxies in 1923 and prove that they were separate colonies of stars, many as large as our own Milky Way.
The following year, a professor at the Swedish Academy of Sciences was so impressed by Leavitt and the power of her cepheid yardstick that he started on the paperwork that would be needed to nominate her for a Nobel prize. But when he began to research Leavitt’s current scientific interests he was shocked to find that she had died of cancer three years earlier. Leavitt was just 53 when she died. Five years after her death, in 1929, Hubble used her cepheids to prove that the universe was expanding, providing the first evidence for the big bang model of the universe.
However, some of Leavitt’s colleagues did receive recognition. Williamina Fleming became the first woman to be designated Curator of Astronomical Photographs, the first corporate appointment of a woman at Harvard. Her achievements were rewarded by election to the Astronomical Society of Mexico, the Astronomical Society of France and the UK’s Royal Astronomical Society. There is even a lunar crater named in her honour.
Similarly, in 1925 Annie Jump Cannon became the first woman to receive an honorary doctorate from the University of Oxford. She was voted one of the 12 greatest American women in 1931 and in the same year became the first woman to receive the prestigious Draper Gold Medal from the American National Academy of Sciences.
In later years, one of the Harvard computers would rise through the ranks to become accepted as a fully fledged member of the astronomical establishment. Cecilia Payne’s doctoral thesis proposed that the stars are predominantly composed of hydrogen. The idea was so controversial that her thesis was rejected at first. But Payne went on to become a Harvard professor in the 1950s, and eventually she became the William Cranch Bond Astronomer at Harvard. The appointment of a woman to such a prestigious post was so rare that the letter announcing her appointment was addressed to “Dear Sir”.
