Cecilia Payne Finds Out What Stars are Made Of

One or twice a year, the story of English-born astrophysicist Cecilia Payne (1900-1979) appears on my Facebook feed. I am enthralle– and enraged–by the story every time. And then I promptly forget her name. A fact that is both frustrating and somewhat embarrassing since this is the kind of story that I firmly believe needs to be known more widely. I hope that by sharing her story with you I can not only spread her story a little further, but anchor it firmly in my brain.

When Cecilia Payne entered Cambridge University in 1919, she knew she wanted to study a science, but did not yet know which one. That changed when she heard a lecture by astronomer Arthur Eddington. Stars were her future.

She quickly realized that she could not have a professional career in astronomy in England. She couldn’t even get a doctorate. In 1923, she came to the United States where she became a graduate fellow at the Harvard College Observatory, which was involved in a long study of the patterns of light emitted by stars, technically known as stellar spectra.* One of the goals of this study was to understand what elements the stars were made of by comparing their spectral lines with those of known chemical elements. Astronomers had already identified heavy elements such as calcium and iron and assumed they were major components of the stars.

Payne applied principles from the new science of quantum physics, which she had studied at Cambridge, to the study of stellar spectra. In her doctoral thesis, the first awarded for work at the Harvard Observatory, she demonstrated that the sun and other stars were composed almost entirely of hydrogen and helium, the two lightest elements—a discovery that overturned previous assumptions. She added a butt-covering caveat to her thesis stating that the abundance of of hydrogen and helium were “almost certainly not real.” She was, after all, a 25-year-old woman in a field in which most women doing scientific work were described as “computers” not scientists.

Like many newly minted PhDs, Payne revised her thesis and published it as a book. Stellar Atmospheres was well received. It was soon accepted that her results were  in fact quite real, and that they profoundly changed what we know about the universe. In 1960, astronomer Otto Struve, no slouch himself in the study of stellar spectra and a founder of radio astronomy, referred to her work as “the most brilliant PhD thesis ever written in astronomy.”

Payne worked at the Harvard Observatory for many years, doing the work of a faculty member with the lower-paid and less-respected title of “technical assistant” to Harlow Shapley, the Observatory’s director. During this period, she published several important books based on her research. In 1956, she was finally made a full professor—the first woman to hold that title at Harvard—and chair of the Astronomy Department.

In 1976, the American Astronomical Society recognized her work as one of the most creative astronomers of the twentieth century, with the Henry Norris Russel Lectureship, which honors a lifetime of excellence in astronomical research.

 

*It should be pointed out that a group of 80 women did much of the laboratory work related to this project.  Hired as “computers” and often ridiculed as “Pickering’s harem,” they literally mapped the heavens. Among other things, they catalogued which stars could be photographed by attaching a spectroscope to a telescope, which records the range (spectrum) of colors which make up starlight. (This is very simplified and possibly even inaccurate.) Once pictures were taken, they classified the spectra displayed in the photographs. They were paid 25 to 35 cents an hour, less that they would have made at a clerical job, and worked six days a week, seven hours a day.
Dava Sobel’s book about this, The Glass Universe, is now high on my TBR list.

Some of the women of the Harvard Observatory, ca. 1910, with the man who hired them, Edward Pickering.

Annie Jump Cannon, one of the women employed by the observatory, had already created a classification system that sorted the spectra of several hundred thousand stars into seven groups based on differences in the spectral features before Payne arrived.** Her system is still in use today.

 

**In other words, Payne’s work depended on the scientific work of another unheralded woman. Cannon was finally given the title of Curator of Astronomical Photographs.

 

 

 

 

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