The Glass Universe

American author Dava Sobel’s non-fiction book, The Glass Universe: How the Ladies of the Harvard Observatory Took a Measure of the Stars (2016), chronicles the efforts of various woman in the late nineteenth and early twentieth centuries to catalog and classify data about stars from photographs captured on thousands of glass plates. In doing work that "no man would stoop to," these women made vital contributions to the field of astronomy and human knowledge in general at a time when opportunities for females in science were rare.

In 1877, the physicist Edward Charles Pickering became the director of the Harvard College Observatory. While there, he captured spectral data on stars with an unprecedented level of detail by projecting photographic images onto glass plates. Compiling and computing this data, however, amounted to an enormous, difficult, and tedious undertaking; Pickering believed that the men working under him were not up to the task. He famously exclaimed, "My Scottish maid could do better!" Then in 1881, Pickering made good on his exclamation, hiring his maid, Williamina Fleming, to assist him in cataloging the data. She later became known as the first of the "Harvard Computers," a group of women tasked with computing mathematical classifications of the stars and editing the observatory's scientific journal publications.

Over the next decade, Fleming devised a new system of classifying stars based on the amount of hydrogen found in their spectra. This system came to be known as the Pickering-Fleming system. Fleming’s other achievements include her discovery in 1888 of the iconic Horsehead Nebula found in Orion's Belt and her discovery of the first-ever white dwarf, a stellar core remnant made up of electron-degenerate matter. In total, Fleming discovered 59 nebulae, 310 variable stars, and 10 novae. Despite these accomplishments, Fleming did not receive credit in scientific literature for her discoveries until 1908. Fleming also noted in her diary that her annual salary of $1,500 was far below the $2,500 salary paid to male astronomers holding similar positions. "And this is considered an enlightened age!" she wrote.



Sobel also details the life and accomplishments of Annie Jump Cannon. After a bout of scarlet fever that left her nearly deaf, Cannon chose to immerse herself in her work as a physicist and photographer. In 1896, Pickering hired Cannon as one of his human computers working under Fleming. Around this time, Anna Draper, the widow of the wealthy physician and astronomy enthusiast Henry Draper, set up a patronage fund to complete the Henry Draper Catalog, which sought to map and classify every star in the sky. Following a dispute between Fleming and Draper's niece, Antonia Maury, over the best way to classify stars, Cannon devised a new classification system that catalogued stars based on their surface temperature, dividing stars into O, B, A, F, G, K, and M spectral cases with O being the hottest and M being the coolest. This classification system is still in use today, and astronomy students memorize it using the mnemonic device, "Oh Be a Fine Girl, Kiss Me." Cannon would go on to manually classify more stars than any other person in her lifetime, totaling around 350,000 stars.

Another key subject of Sobel's book is Henrietta Swan Leavitt. Like Cannon, Leavitt was also deaf. In 1898, she joined Pickering's staff of Harvard Computers, initially doing the work as a volunteer because she came from a family of means. In 1912, she published her discovery of a relationship between luminosity and the pulsation period of Cepheid variable stars. This discovery had a massive impact on the field of astronomy. It directly led to the ability of astronomers to measure the distance to faraway galaxies. Years after her death, Edwin Hubble relied on her research along with that of others to establish that the universe is expanding. Through her work, Leavitt also refined and improved the photographic standards used in observatories around the world.

After Pickering's death in 1919, Harlow Shapley took over as director of the Harvard College Observatory. He continued to hire and employ women, including Cecilia Payne-Gaposchkin. At Shapley's urging, Payne-Gaposchkin wrote a doctoral dissertation in astronomy. In it, she showed that stars were comprised primarily of hydrogen and helium, bucking the scientific consensus at the time that stars were comprised of the same elements as the planet Earth. In large part, because she was a woman, wide swaths of the scientific community roundly rejected Payne-Gaposchkin's conclusions. Later research, however, would prove her conclusions correct. For her dissertation, Payne-Gaposchkin became the first woman to receive a PhD in astronomy. This marked a turning point at the Harvard Observatory, lending greater mainstream credibility to women's achievements in astronomy than ever before.



The Glass Universe offers an inspiring depiction of the women who changed astronomy and humanity's understanding of the universe.