History: Women who read the stars

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Sue Nelson delights in Dava Sobel's account of a rare band of human computers.

The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars

Dava Sobel Viking: 2016. ISBN: 9780670016952

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Courtesy Harvard Univ. Archives

Some of the Harvard Observatory 'computers' in 1925. Annie Jump Cannon is seated fifth from left; Cecilia Payne is at the drafting table.

There are half a million photographic plates in the Harvard College Observatory collection, all unique. They date to the mid-1880s, and each can display the light from 50,000 stars. These fragments of the cosmos furthered our understanding of the Universe. They also reflect the dedication and intelligence of extraordinary women whose stories are more than astronomical history: they reveal lives of ambition, aspiration and brilliance. It takes a talented writer to interweave professional achievement with personal insight. By the time I finished The Glass Universe, Dava Sobel's wonderful, meticulous account, it had moved me to tears.

In the nineteenth century, US women had no vote (that would come in 1920). The careers open to the vast majority were in domestic service, farms, factories, schools or offices. Fortunately, Maria Mitchell, the first woman in the United States to discover a comet, left a guiding light. In 1865, she became the first professor of astronomy at Vassar College in Poughkeepsie, New York, a new institute of higher education for women.

Yet change was slow. When Edward Pickering became director of the Harvard Observatory in Cambridge, Massachusetts, in 1877, being a 'computer' was still predominantly a man's job. This low-paid but essential work involved noting a star's brightness, or magnitude, on the photographic plates and computing its location in the sky. Pickering was especially interested in variable stars, whose light would brighten and fade over a specific period. These fluctuations, captured on the plates, required constant observation, but he couldn't afford extra staff.

Some years later, opportunity arrived in the form of the wealthy Anna Palmer Draper, widow of amateur astronomer and physician Henry Draper. She set up a memorial to fund his great ambition: to photograph the night sky and create a spectral catalogue of the stars. When starlight is split by a prism or spectroscope at the end of a telescope, it can produce a tiny grey smudge, millimetres long, on a photographic plate. The separated light, on closer examination, reveals vertical black spectral lines. This stellar barcode provides a star's chemical composition, colour and temperature.

By 1883, six women were already working as computers at Harvard, a practice unique to the university. Within five years, the number of paid female computers, from a range of backgrounds, had risen to 14. Their efforts would be boosted by philanthropist Catherine Wolfe Bruce, who in 1889 donated US$50,000 to the observatory, convinced that the introduction of photography and spectroscopy would advance the field.

The Glass Universe concentrates on a few of the Harvard computers. Williamina Fleming, a Scottish school teacher, arrived at the observatory in 1879, pregnant and abandoned by her husband. Pickering employed her as a maid and housekeeper before promoting her to computer in 1881. Fleming discovered more than 300 variable stars and, in 1899, became Harvard's first curator of astronomical photographs. She and Pickering revised the classification of stars using their spectral lines, labelling them alphabetically from the bluest, hottest stars to the coolest red stars.

Henrietta Swan Leavitt, who studied at another women's institution, Radcliffe College in Cambridge, began as a volunteer in 1895, gaining a permanent post in 1903. Five years later, she determined the relationship between luminosity and period of fluctuation for a class of pulsing variable stars called Cepheids. That enabled astronomers to calculate a star's distance from Earth, and in 1918 allowed Harlow Shapley, who would become Pickering's successor, to extend the boundaries of the Milky Way. Leavitt's work also laid the foundation for Edwin Hubble's finding, in 1925, that our Galaxy was not a lone 'island Universe' but one of billions. In 1929, Hubble used Leavitt's work and spectral shifts to show that this populous Universe is also expanding.

Annie Jump Cannon arrived in 1896, following studies in mathematics, physics and astronomy at another women's college, Wellesley, in the Massachusetts town of the same name. She refined and simplified the Pickering–Fleming system of stellar classification by proving that most stars were of a similar type. The International Astronomical Union adopted her system in 1922, three years after Pickering's death.

Cecilia Payne, educated at the University of Cambridge, UK, came to the observatory on a fellowship in 1923, under Shapley. As part of her PhD, she determined correctly that stars were predominantly composed of hydrogen and helium. In 1956, she became Harvard's first female professor of astronomy.

Payne provides some of the book's most touching passages. Sobel describes, for instance, Payne's distress at the untimely death of her friend and fellow computer Adelaide Ames in 1932, and her whirlwind romance with the astronomer and Russian émigré Sergei Gaposchkin, whom she married in 1934. Later that year, Payne won the inaugural Annie Jump Cannon Prize for contributions to astronomy, receiving $50 and a gold pin, designed by Cannon, in the form of a spiral nebula.

These personal touches flesh out the women's lives. We are shown Payne, for instance, pawning her violin and jewellery to fund her research, and combining motherhood with astronomy. The low wages were a sticking point with many of them — Fleming often mentions it in her diaries. Yet, as Sobel shows, they clearly liked and admired Pickering and Shapley, who encouraged their work and facilitated their professional progress.

One of the last computers in the twentieth century, Radcliffe alumna Ellen Dorrit Hoffleit, gets a brief mention towards the end. She joined the observatory in 1928. In 2004, I met her at Yale University in New Haven, Connecticut, when I was making a radio documentary for the BBC on the Harvard computers. An energetic 96, Hoffleit was working on a paper about meteors. Like all of this band of remarkable women, she was unforgettable, as is this book.

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