Culture | How women rose to the top of American astronomy

Looking at the stars

The work of the ladies team of the Harvard Observatory

The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars. By Dava Sobel. Viking; 324 pages; $30. To be published in Britain by 4th Estate in January.

IN THE late 19th century an extraordinary group of women worked at the Harvard College Observatory. Known as “computers”, they charted the position and brightness of stars on a daily basis by applying mathematical formulae to the observations of their male colleagues who watched the sky. Harvard was unique in taking advantage of the burgeoning numbers of educated women in this way. When the observatory’s research was redirected towards photographing the heavens rather than observing them merely by eye, the duties of the “computers” expanded apace. Many of them would go on to extraordinary achievements in astronomy.

The work of Harvard’s female staff was paid for largely by two other women, Anna Palmer Draper and Catherine Wolfe Bruce, heiresses with an enduring interest in astronomy. Dava Sobel, a former science writer for the New York Times who made her name with her bestselling first book, “Longitude” (1995), has spent several years poring over letters and studying archives in order to tell the story of the women-astronomers and their benefactors.

The introduction of photography at the Harvard Ovservatory allowed the firmament to be captured on an unprecedented scale on eight by ten-inch glass plates. These plates, about half a million in all by 1992, when the observatory switched to digital storage methods, comprise the “glass universe” of her book’s title. They allowed the course of stars to be followed not just for a few nights, but for decades. Discoveries made by astronomers on other continents could be cross-checked with Harvard’s library. Perhaps more important, when starlight was split with the aid of a prism its spectrum could likewise be recorded.

These spectra resemble long rainbow-coloured strips (rendered in black and white on the plates’ photographic emulsion) interspersed with numerous dark lines. Scientists would come to understand that the gaps in a spectrum are due to the absorption of light by the atoms of chemical elements that compose a star’s outer layers. As one astronomer triumphantly declared, the ability to divine a star’s constituents from its spectrum “made the chemist’s arms millions of miles long”. Stellar spectroscopy would also reveal other physical attributes of stars such as their temperature, eventually giving rise to the new field of astrophysics.

This extraordinary photographic record offered the Harvard Observatory team the chance to learn a great deal more about the stars. During routine studies of the plates in 1893, for example, Williamina Fleming found a nova, only the tenth to have been observed by astronomers in the West. She would go on to discover nine more. Annie Cannon catalogued hundreds of thousands of stars, in the process inventing a stellar classification system that is still in use by astronomers today. The cyclical dimming and brightening of variable stars fascinated Henrietta Leavitt, who became the first person to realise that the frequency of their pulsation was directly related to their brightness. This allowed astronomers to reliably measure how far away they were, to establish the gargantuan dimensions of the Milky Way, and the even greater distances between this galaxy and others. Perhaps most remarkable of all was Cecilia Payne, the first Harvard student (man or woman) to be awarded a PhD in astronomy. Her thesis in 1925 ascertained that, relative to the proportions of other elements, hydrogen is vastly more abundant in stars than it is on Earth.

On seeing her thesis, Henry Norris Russell, an expert on the chemical composition of stars, told her that the result was “clearly impossible”. Four years later, Russell’s own calculations would lead him to admit that Payne had been right after all. The prevalence of hydrogen, he wrote at the end of his paper, “can hardly be doubted”. Unjustly, it was Russell at the time, not Payne, who was frequently credited with the discovery.

The few grumbles expressed by the “computers” of Harvard Observatory will be familiar to many women (and, to be fair, some men) within the academy today. “Sometimes I feel tempted to give up and let him find out what he is getting for $1,500 a year from me,” Fleming wrote in her journal after unfruitful salary negotiations with the director, “compared with $2,500 from some of the other [male] assistants.” Indeed, the directors seemed at times to have something of a sweatshop mentality towards their diligent assistants. Another boss measured computing tasks in units of “girl-hours” and “kilo-girl hours”.

Ms Sobel is keen to absolve the directors of this charge. But there is no getting away from the fact that had they been occupied with fewer humdrum labours, the brilliant women whom she portrays in her book might well have achieved even more than they did. Afficionados of astronomy may be familiar with their names; now it is time they were known to a wider audience. Ms Sobel has drawn deeply from her sources, knitting together the lives and work of the women of Harvard Observatory into a peerless intellectual biography. “The Glass Universe” shines and twinkles as brightly as the stars themselves.

This article appeared in the Culture section of the print edition under the headline "A secret history"

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