On December 25 the American astronomer Vera Rubin, whose discovery that galaxies were rotating too fast given the mass of their constituent stars provided evidence for the theory of dark matter, died at the age of 88. Her obituaries note the challenges Rubin faced as a pioneering woman in an overwhelmingly male field: prevented from doing graduate work at Princeton, she got her Ph.D. at Georgetown in 1954; in 1965 she became the first woman allowed access to the Palomar Observatory. In the June 2016 issue of Astronomy, Sarah Scoles decried the fact that Rubin’s discovery was somehow insufficient for a Nobel Prize, which she will now never win.

Inasmuch as Rubin was a pioneer, she was not the first woman in astronomy, nor the first to obtain a Ph.D., nor the first to be responsible for a discovery that fundamentally reshapes our understanding of the cosmos—nor the first for whom recognition was unfairly delayed. Some of the women who came before her are the subject of Dava Sobel’s new book, The Glass Universe, coincidentally out this month from Viking.

From the 1880s to the 1980s, the Harvard College Observatory amassed a collection of half a million glass photographic plates of the night sky, and catalogued hundreds of thousands of stars’ luminosity and spectra. The work, along with some significant scientific discoveries, was largely done by a group of women known as the Harvard Computers. If you watched Cosmos: A Spacetime Odyssey, you saw a bit of this in the eighth episode, “Sisters of the Sun,” which talked about the computers, especially Annie Jump Cannon, as well as Cecilia Payne, who used the computers’ data to redefine our understanding of the makeup of stars.

The Glass Universe charts the history of the group, from the bequest by Henry Draper’s widow, to Observatory director Edward Charles Pickering’s decision to hire women to do the work (less expensive), to the achievements and discoveries that followed. It’s not a scholarly work, though it’s assiduously researched, drawing on the correspondence of the principal figures. Nor is it an explicitly feminist analysis, or for that matter strictly focused on the women themselves, as the narrative takes the reader far and wide, to remote stations in Peru and South Africa. Sobel (whose previous work includes Longitude, the story of Harrison’s chronometers) provides context, and a whole history, to help us understand not only who these women were, but what they accomplished.

The sheer volume of data collected—Pickering agonized over losing the irreplaceable glass plates to fire—was the basis not only of the Bright Star Catalogue and the Henry Draper Catalogue (if you see a star identified by a number with an HD prefix, that’s where it came from), but of the discoveries that resulted from the mass of data collection, and the fact that the principals stayed at their work for decades, building up a wealth of experience and perspective at, frankly, graduate student pay rates.

It is a paradox of popular culture that while the women of the Observatory who made these discoveries received credit for their work—first in acknowledgements in Pickering’s own work, later as co-authors and authors in their own right, and in the honours they eventually received from their peers (though not, it must be said, from Harvard University itself)—their names have not penetrated the popular-science zeitgeist to the same extent as, say, Hubble’s, Lowell’s or Tombaugh’s. You might argue that stellar spectra are a more rarefied subject, but I’d counter that (a) we know who Hubble is, and his discoveries are a direct consequence of their work; and (b) I knew what their discoveries were, I just didn’t know who made them.

I knew, for example, about the system of stellar classification based on stellar spectra (“Oh Be A Fine Girl Kiss Me” and all that), but I didn’t know that it was developed by Annie Jump Cannon—as a compromise between earlier systems devised by Williamina Fleming and Antonia Maury. Classifying stars was long, tedious, repetitive work—women’s work—but it was vital, and enduring.

I knew what a Cepheid variable was, and how the relationship between its pulsation and its luminosity allowed it to be used to calculate interstellar (and later intergalactic) distances; I didn’t know that this relationship had been discovered by Henrietta Swan Leavitt. And it was Cecilia Payne (later Cecilia Payne-Gaposchkin) who determined that Cannon’s spectral classes were a function of temperature, and that stars were mainly made up of hydrogen and helium. These are fundamentals of stellar astronomy, and these women were the ones who discovered them.

I’m trying to reconcile the hostility Rubin faced with the relatively warm reception given the women of the Harvard College Observatory. It’s possible that Rubin’s obituaries and Sobel’s book are each reporting a different side of the same coin: the story in both cases is incomplete. But the women of the Observatory were likely seen as exceptional, which is to say exceptions, and as such less of a threat to the profession. In any case, the field needed their work, their data and their discoveries, and was happy to have it. And in the end, the Harvard Computers, once referred to as “Pickering’s Harem,” managed to transcend what in science is called the “harem effect”—the hiring of large numbers of female subordinates at lower pay—to reshape our understanding of the stars.

See also NPR’s review of The Glass Universe and National Geographic’s interview with Dava Sobel.

I received an electronic review copy of this book via NetGalley.

The Glass Universe
by Dava Sobel
Viking, 6 Dec 2016
Amazon (Canada, UK) | Apple Books | Bookshop