In the 1880s, Edward Charles Pickering, the director of the Harvard College Observatory, started amassing what would eventually become the world’s largest collection of photographic plates of stars—500,000 slices of the sky captured on glass.

Many of the images were carefully ferried from observatories not just in North America, but also Peru, South Africa, New Zealand, and Chile. In the Peruvian Andes, a single Harvard astronomer would pack the delicate plates into two wooden crates and carry them down from a mountain, nicknamed Mount Harvard, “on muleback and across a suspension bridge,” according to The New York Times. From there, they traveled on a train to Lima before making it on board a Boston-bound boat to the university.

To analyze this abundant stream of data, Pickering relied on a team of women. Some came to him with college educations, and others received on-the-job training. Gathered in a small library, adjacent to the observatory, they would work for about 25 cents an hour, six days a week, calculating the temperature and motion of the stars via these astronomical plates.

By discovering new stars, nebulae, and novae—and going on in their careers to shape the then-emerging field of astrophysics with their spectral analyses of stars—these “Harvard Computers” gained recognition around the world over the decades for their contributions to astronomy. Their efforts paved the way for women who would work in computing, engineering, and aerospace industries as human computers.

A negative of the Andromeda galaxy from the Harvard archives
(Jenny Woodman)

The stories of the women who followed in the Harvard ladies’ footsteps have recently been documented in books such as The Rise of the Rocket Girls and Hidden Figures. But the Harvard Computers’ story remains largely unexplored. In The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars, out on December 6, Dava Sobel, the author of Longitude and Galileo’s Daughter, has painstakingly recreated their efforts to explore the heavens.

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.

Woodman: You begin your book with Pickering’s benefactress, Anna Draper. She funded much of Harvard College Observatory’s work during Pickering’s reign in order to honor her late husband, Henry Draper, a devoted and enthusiastic amateur astronomer. What intrigued you about her?

Sobel: Her circle is really interesting. She was very privileged. She mentioned somebody in her letters to Pickering who was the head of the Library of Congress at the time. She was friendly with judges. She knew Edison. She got Edison to give some equipment to Harvard. She had a tremendous reach.

Woodman: Yes, Anna’s reach was one of the many coincidences that were necessary for the observatory’s success. That’s something that struck me about the story of Cecilia Payne, one of the more famous astronomers at Harvard. She just happened to be at Cambridge where her professors were discovering atomic elements (and winning Nobel Prizes for their efforts). Then, Cecilia arrives at Harvard in 1923 as the first graduate student under Shapley, armed with all this new knowledge, which would transform astronomy.

Sobel: I agree with you. I think it's an incredible coincidence!

Woodman: Is there one of the ladies you feel a particular affinity towards?

Sobel: I'm just crazy about Annie Jump Cannon. She had a great wit. She did not have a heightened sense of self-importance. When she really did something, then she didn't shy away from it. I love a comment she made about how when she got put on the [Committee on Classification of Stellar Spectra, in Bonn, Germany, in 1913]—since she was the person who had done most of the world's work in that area, she had to do most of the talking.

A page from Annie Jump Cannon’s line-a-day diary in the Harvard archives
(Jenny Woodman)

Woodman: I visited Harvard’s archives, and I was surprised to open a box filled with those tiny leather-bound books, Annie’s journals. She kept line-a-day diaries for so many years. I tried reading them and found it quite challenging, between their brevity and the handwriting. How did you go about piecing together such a rich narrative about Annie?

Sobel: I selected certain years. I looked through 1920 because I wanted to know how she reacted to the right to vote. Then, I wanted Adelaide Ames’s death.

Opening those [archival] boxes and seeing all the little books inside, I was just knocked out by that. It really felt like a sonic boom. There was something so girlish about them. She had stuck to it her whole life; I've never seen anything like that, such a complete record. She saved every program from every opera, every libretto—this woman is deaf, or she's described that way. Apparently, she could hear well enough to continue her love of music, lifelong. I tried to communicate to the head of the archives that the record of her life is complete to an extent, considering the time period. I think it's exceptional.

Her correspondence with the guy who was the head of the Royal Astronomical Society—his letters to her about the conditions on the ground during World War I. He had two sons in the Army; one of them had shell shock and was sent somewhere for treatment. He wrote her long [letters], the detail of what the food situation was like in London and how young men had disappeared from the streets. It was magnificent. She reciprocated in her letters.

She had that kind of correspondence with so many people. She got involved with everybody's children. Then, she would correspond with the children. The correspondence goes on for some number of years and then there's an invitation to the wedding. She was just a thoroughly wonderful character.

Woodman:  Because women had such a tangible presence at the observatory for so long, when Shapley, Pickering’s successor, decided to launch a graduate education program and begin granting doctoral degrees, he offered the first spots to female students, right?

Sobel: Yes, special grants in aid to women, secured with Pickering’s help, became the first stipends for graduate students—all of whom were female during the program’s first three years.

Woodman: Why is this story so important for us to read today?

Sobel: [One of the plate curators] made a really funny remark, which was: “Women have always been in the past, they just haven't been part of history.” The more I learned about the [women], I discovered that they did real work. They were given tremendous responsibility and autonomy. It wasn't scud work, although it's often portrayed that way.

I first heard about the [Harvard Computers] from Wendy Freedman, who was part of Carnegie Observatory; she was in charge of one of the Hubble key projects. She mentioned Henrietta Leavitt because of the period-luminosity relation and how important that was, still, in figuring out the age and size of the universe. I had never heard of Henrietta Leavitt. That got me interested in her and that period. Then, I realized there was a whole room full of these women, and that was remarkable.