I spoke to Sobel about her newest book and the women of Harvard College Observatory. Our conversation has been condensed and edited for clarity.

Jenny Woodman: Who were the women Pickering recruited? What were their day-to-day lives like?

Dava Sobel: When he arrived at the Observatory, in 1877, Pickering found astronomers’ family members—wives, sisters, daughters—already acting as assistants. As the need for personnel increased, he sought additional women who were good at math and had office experience. Within a decade, he hired his first female college graduate.

By then, Pickering’s focus on photography had created a new source material for the ladies, in the form of glass photographic plates. The women worked, usually in pairs, with one partner looking at a plate and speaking aloud her findings to the other, who recorded them in a notebook.

Woodman: What were they looking for?

Sobel: At first, much of the women’s work entailed computing the actual positions and brightness of individual stars by applying mathematical formulae to the nightly notations made by the male observers. With the glass plates, they could discover new stars. While some of the photographs portrayed the stars as dots to be counted and catalogued according to sky coordinates, other images displayed the stars’ light as tiny strips, or spectra, bearing distinct patterns.

A few of the women were challenged to make sense of these patterns by devising a scheme for sorting the stars into categories. Annie Jump Cannon’s success at this activity made her famous in her own lifetime, and she produced a stellar classification system that is still in use today. Antonia Maury discerned in the spectra a way to assess the relative sizes of stars, and Henrietta Leavitt showed how the cyclic changes of certain variable stars could serve as distance markers in space.

Woodman: The observatory directors—Pickering and his successor, Harlow Shapley—were really quite progressive. They advocated for women’s suffrage and gave credit to the “computers” for the work they were doing. Pickering even used crowdsourcing and citizen science. He knew that there was no way the observatory staff could perform the necessary observations, so he reached out to amateur astronomers for data collection. I was surprised to see something so popular today occurring in the 1800s.

Sobel: Crowdsourcing, yes. Having all these women who had a college education and a telescope, why don't you volunteer to help us? [Pickering] really was terrific.

Woodman: These women, to me, were so wonderful, but their story often reduced to jokes about “Pickering’s Harem.”

Sobel: Maybe [the women] are unsung heroes, but in their own time, they were not unsung at all. Here they were getting their name in all the publications, getting invited to be foreign members of astronomical societies.