Review of “The Glass Universe” by Dava Sobel

This non-fiction account, subtitled “How the Ladies of the Harvard Observatory Took the Measure of the Stars,” is a history of the Harvard College Observatory and the women who both funded the scientific program there and performed a great deal of the research.

The women workers functioned as “computers” at a time when the machines we today call computers were not yet in existence. Many of the women came to the observatory when young and spent the rest of their lives doing astronomical work. There were six of them at first, later expanding to 14. They toiled for hours over glass plates of the stars made by astronomers in both the northern hemisphere at Harvard, and at Harvard’s southern outpost in Arequipa, Peru.

Stars show up as black dots in this negative plate of the Small Magellanic Cloud, a satellite galaxy of the Milky Way that can be seen from the Southern Hemisphere. (Courtesy Harvard College Observatory)

The women subdivided the sky and examined the plates from each stellar region. They analyzed and recorded the brightness of each star with respect to the others on the plates, and looked for oddities – especially new and/or variable stars. They also identified the spectra of all of the stars. (Prisms inside the telescopes split the light of each star, revealing barcode-like lines indicating properties of stars such as chemical composition and temperature.)

Spectrum of the sun

The glass universe that grew in size year by year paralleled the one revealed above astronomers’ heads with ever stronger telescopes.

Right from the outset, the author tries to disabuse readers of the commonly held notion that the female workers at the Harvard Observatory were underpaid and undervalued because they were women. Yes, they were paid pittance wages, but so was everyone else at the observatory; money for research was scarce. And they were far from undervalued. In fact, Edward Pickering, head of the Harvard Observatory for over 40 years – from 1877 to 1919, did all that he could to give credit to the women’s findings and to advance their positions. His successor, Harlow Shapley (Director from 1921 to 1952), did even more.

Edward Pickering

The most significant finding derived from the glass plates, one in some ways as earth-shaking as the findings of Galileo, was made by Henrietta Swan Leavitt, one of the “computers” at the observatory. She discovered that a certain type of pulsating star, called a Cepheid Variable, always exhibited a direct relationship between brightness and its period of alterations in brightness. The brighter the magnitude, the longer the period – always. So if one Cepheid Variable was not as bright as another but had the same period, it must be farther away, and that distance could be calculated mathematically. Cepheid variables became the markers of distance in space. Her discovery not only enabled astronomers to calculate distances in space, but showed that the Milky War was not the only galaxy in the universe, a truly revolutionary finding. Later, it helped demonstrate that the universe was expanding.

Henrietta Swan Leavitt

As a Nasa website points out,

“This method works up to 13 million light-years when Earth-bound telescopes are used. . . . Recently, space-based telescopes such as the Hubble Telescope, have used these stars to much farther distances. Looking at a galaxy in the Virgo cluster called M100, astronomers used the Cepheid variables observed there to determine its distance – 56 million light-years.”

Although one purpose of this history is to highlight the achievements of the women at the observatory, Pickering plays a central role. He worked tirelessly to get whatever funds he could to operate the observatory and to reward budding astronomers. He helped usher in a new era that employed photography and spectroscopy to take astronomical findings to the next level. He ensured that the library of the glass plate universe was expanded, protected, and made available to any wishing to study the stars.

Astronomers no longer use glass plates, since everything is done digitally. But this does not mean the glass universe is without value. On the contrary, as the author observes:

“ . . . no matter how broadly or deeply modern sky surveys probe outer space, they cannot see what the heavens looked like on any given date between 1885 and 1992. The record preserved in the Harvard plate collection of one hundred years of starry nights remains unique, invaluable, and irreplaceable.”

“Pickering’s Harem,” so-called, for the group of women computers at the Harvard College Observatory

Today, astronomers regularly consult the plates (over 500,000 of them!) to enrich and interpret their latest findings: “Celestial denizens undreamed of at the start of Pickering’s sky patrol – pulsars, quasars, black holes, supernovae, X-ray binaries – nevertheless left their marks on the plates.”

Evaluation: This tribute to tireless scientists including a small dedicated circle of women is well worth reading for an appreciation of the enormity of the effort of many people over many years behind scientific discoveries. Sobel also makes the point that while the men were generally assisted by wives, the women scientists who worked so long and so hard, also had homes and families to take care of, and they did it all.

Rating: 3.5/5

Published in hardcover by Viking, an imprint of Penguin Random House, 2016

A Few Notes on the Audio Production:

This book was narrated admirably by Cassandra Campbell, who makes even the introduction of chapter numbers sound beautiful. She seamlessly takes on the pronunciation of different places in different languages, and it was a pleasure to listen to her.

Published unabridged on 10 CDs (approximately 12 and 1/2 listening hours) by Penguin Random House Audio, 2016

Addenda: Harvard University is working to digitize and transcribe notebooks from some of Harvard College Observatory’s most famous women computers, including Henrietta Leavitt and Annie Jump Cannon. They are looking for volunteers to help from home! You can read more about this and find out how to get involved here.


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6 Responses to Review of “The Glass Universe” by Dava Sobel

  1. BermudaOnion says:

    Some things never change for women, it seems. I find these stories fascinating and am glad to see them getting some attention.

  2. Kay says:

    That is really interesting! I saw something about this book a while back and thought it would be fascinating to read. Glad to know the audio is well done. And, also, thanks for sending the info about helping with transcription of the documents, etc. Had no idea there was such a thing as volunteering for that sort of duty. I might check it out!

  3. Angela says:

    This sounds like a really interesting book. I’m so happy that books like this are being written because women’s history is so often ignored. I read a really interesting book in December called Code Girls (about women code breakers during World War 2) and I was shocked by the enormous contribution women made to that war because they get so little attention or credit for all they did.

  4. Beth F says:

    I like Sobel (Longitude was great), so have been meaning to reading this. And good news that Cassandra Campbell is the narrator because I usually really like the way she reads.

  5. Trisha says:

    This sounds like a great read! I will be on the lookout for those transcribed notebooks. I probably won’t understand much, but I love reading people’s notes. 🙂

  6. mae says:

    Sobel’s earlier books, especially Galileo’s Daughter, were wonderful. Thanks for the review of this new one. I should read it!

    best… mae at

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