Cecelia Payne
Cecelia Payne-Gaposchkin at Harvard College Observatory Smithsonian Institution / Science Service, restored by Adam Cuerden - Air and Space Museum online gallery / Public Domain
Astronomer Cecilia Payne-Gaposchkin spent nearly a year in “utter bewilderment” after arriving at the Harvard College Observatory in the early 1920s. She often worked into the late evening and felt “in a state of exhaustion and despair,” she later wrote in her autobiography.
The fruits of her labor would earn her an important place in the history of astronomy. A century ago this year, her 1925 doctoral thesis presented a controversial idea: that hydrogen and helium dominate stars.
“She was the one who really broke down for the first time: What are stars made out of?” says Natalie Hinkel, an astrophysicist at Louisiana State University.
But Payne-Gaposchkin faced resistance both to her revelation and in her career as an astronomer more generally. Today, we know that she was right, and that these elements also constitute the vast majority of the ordinary matter in the universe. Her thesis paved the way for the modern study of stars and galaxies, and contributed to the search for habitable planets, and even life, beyond our solar system.
Beginnings
Born in 1900 in Wendover, England, as Cecilia Payne, she studied botany, chemistry and physics at the University of Cambridge. She became drawn to astronomy when she heard Arthur Eddington speak about his victorious 1919 expedition to view a total solar eclipse, and how the results of his experiments confirmed Einstein’s theory of general relativity. Afterward, she didn’t sleep for three nights. “My world had been so shaken that I experienced something very like a nervous breakdown,” she wrote in her autobiography.
Being a woman limited her career prospects in England to teaching. In the United States, she had a better chance of becoming an astronomer—especially if she could get to Harvard. Since the late 19th century, the Harvard College Observatory employed women as “computers” to analyze and catalog glass plates containing astronomical data. Their work led to many important discoveries and innovations, such as Annie Jump Cannon’s classification of stars still in use today.
The observatory’s director Harlow Shapley gave an astronomy lecture in the early 1920s in England where “a tall young woman” attended and “just drank it in,” he recalled in an oral history interview archived at the American Institute of Physics. Payne-Gaposchkin says in her autobiography that after this lecture she told Shapley directly that she wanted to work for him. She earned a fellowship and crossed the ocean to do just that.
“Her personality was very sharp and strong,” says Deborah Shapley, a granddaughter of Shapley and founder of the Harlow Shapley Project, which is dedicated to raising awareness of Shapley’s achievements and legacy. “She had a great passion for her science and was extremely articulate in the manner of a British educated person of that time,” she says.
Harvard Computers
Harvard “computers” at work at the end of the 19th century Harvard College Observatory / Public Domain
Harvard’s immense collection of astronomical plates, containing images and spectra from many telescopes worldwide, seemed so precious that Payne-Gaposchkin hesitated to touch them and asked Shapley what would happen if she broke one. “When a little later I inadvertently sat down on a pile of plates, I rushed out of the observatory and did not dare to return for several days,” she wrote in her autobiography. “Fortunately no damage had been done.”
Connecting the dots
Most astronomers of the early 20th century were essentially “catalogers,” charting where the stars were rather than probing their nature, says David DeVorkin, historian emeritus at the Smithsonian’s National Air and Space Museum. Few had the training and orientation to be able to apply theories about atomic physics to the study of the stars.
Back in England, lectures from Niels Bohr and coursework from Ernest Rutherford had exposed Payne-Gaposchkin to the leading ideas about matter at the tiniest scales. So Payne-Gaposchkin had that rare combination of knowledge plus access to Harvard’s enormous astronomical archive, enabling her to make a groundbreaking discovery.
“She’s taking quantum mechanics, what at the time was this relatively new understanding of the way that atoms work, and she’s applying it to this library of stellar spectra,” says Mia Bovill, an astronomer and research scientist at the University of Maryland.
Spectra are patterns of lines that serve as fingerprints of atoms and molecules. An instrument on a telescope called a spectrograph spreads light out in a way that produces these patterns. By analyzing these lines, scientists can analyze how light is absorbed by the outer gas layer of a star and determine composition, temperature and pressure.
Payne-Gaposchkin measured the intensities of the spectral lines from different stars on the Harvard plates. Then, she made use of relatively new methods to determine the abundances of elements based on a spectrum of a gas. Those equations came from Indian astrophysicist Meghnad Saha, with revisions from scientists Edward Arthur Milne and R.H. Fowler.
By relating the spectral lines to the temperatures and abundances of elements in stars, Payne-Gaposchkin refined and explained temperature estimates for the different classifications of stars, for which her colleague Cannon had laid the foundation.
This work must have been painstaking before the invention of the hand calculator, Bovill notes. Today, Bovill says, “these equations are taught to graduate students, but we now use computers to solve them.”
Toward the end of the thesis, Payne-Gaposchkin included her most groundbreaking results in a chart showing the relative abundances of different elements in stars. There, for the first time, it was demonstrated that hydrogen dominates stars, followed by helium, and then everything else. Hydrogen, it seemed, was a million times more abundant than metals like aluminum and silicon.
“To me, that is one of the most fundamental discoveries in the history of astrophysics,” Bovill says.
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Walking it back
But Payne-Gaposchkin didn’t get to trumpet her revelation about hydrogen and helium in stars. Princeton University astronomer Henry Norris Russell, who had been Shapley’s own mentor during graduate studies, served as an external advisor to the Harvard Observatory. He read Payne-Gaposchkin’s thesis draft and wrote to her that the high abundance of hydrogen compared to heavier elements is “clearly impossible.”
Was Russell’s take colored by the fact of Payne-Gaposchkin being a woman? DeVorkin, the historian, who wrote a biography of Russell, doesn’t think so.
At that time, many astronomers thought that stars would have the same chemical elements as the Earth, in roughly the same proportions. What’s more, Payne-Gaposchkin’s methods hinged on ideas from Saha that weren’t universally accepted. Payne-Gaposchkin’s demonstration that hydrogen and helium dominate stars was “such a radical conclusion” that Russell felt it needed more evidence, DeVorkin says.
Payne-Gaposchkin, being politically savvy, took Russell’s guidance and critiques seriously. In the version of her paper published as a thesis, she writes that her abundances for hydrogen and helium are “improbably high” and “almost certainly not real.” Despite this downplaying, DeVorkin notes in a 2010 article in theJournal of Astronomical History and Heritage, Payne-Gaposchkin kept the core conclusion in the thesis, “in a manner that was designed to record for posterity that she was the first to make this observation, right or wrong.”
Pushing it forward
Payne-Gaposchkin’s thesis, which she published as a book, represented the first doctoral thesis in astronomy at Harvard. Just a few years later, in 1929, Russell, who had told her to soften her characterizations of her findings, published a journal article arriving at the same conclusion as Payne-Gaposchkin: that hydrogen and helium constitute most of the sun, using different methods.
While Russell did cite Payne-Gaposchkin, writing that he found “very gratifying agreement” with her results and his own, he had far more fame already in the field. Russell’s unofficial title, “Dean of American Astronomers,” is tied to his ability to “convince astronomers that a radical conclusion was in fact real,” DeVorkin says. Both Payne-Gaposchkin’s and Russell’s papers received citations in the ensuing years, but according to Google Scholar, his had amassed more than three times as many as hers by 1965. (By the same metric, around 100 works have referenced Payne-Gaposchkin’s thesis since 2005, representing a huge uptick).
We may never know Payne-Gaposchkin’s feelings upon Russell’s publication, but she writes in her autobiography that he was not good about giving credit to his colleagues who played a huge part in his work, including the astrophysicist Charlotte Moore Sitterly. “It did not, I think, ever occur to him that he might be exploiting those who worked under him,” Payne-Gaposchkin wrote.
Regardless, Payne-Gaposchkin’s discovery reverberated into something even bigger years later. In 1948, scientists began thinking about how hydrogen and helium could have formed in the Big Bang, which turned out to be the reason why these elements are so prominent in the universe. Astronomers Otto Struve and Velta Zebergs, in the 1962 book Astronomy of the 20th Century, called Payne-Gaposchkin’s doctoral work “undoubtedly the most brilliant Ph.D. thesis ever written in astronomy.”
Payne-Gaposchkin remained at Harvard for decades and received several prestigious accolades during the course of her career, but she continued to suffer the prejudices against women in astronomy at the time. For example, women faced obstacles in observing at telescopes. “Those in charge often thought it was too dangerous to have women observe alone and improper for them to spend the night in the company of men,” Peggy Kidwell, now a retired curator of mathematics at the Smithsonian’s National Museum of American History, wrote in the introduction to Payne-Gaposchkin’s autobiography, which was published posthumously in 1984.
What’s more, staff appointments at universities were scarce. Harvard paid Payne-Gaposchkin as Shapley’s “technical assistant” even though she taught graduate students, and the college did not list her courses in its catalog until 1945, Kidwell wrote.
Nonetheless, Payne-Gaposchkin—who eventually married fellow scientist Sergei Gaposchkin—made inroads at Harvard. In 1956 she became both Harvard’s first female professor and department chair, and she remained active in astronomy for the rest of her life. Three years before her death in 1979, she received a prestigious award named for the advisor who told her that her conclusions were impossible: Henry Norris Russell.
The stories of Payne-Gaposchkin and the Harvard women “computers” are especially meaningful to Bovill as a practicing astrophysicist today. “To have the names of these women who, 100 years earlier, had done phenomenal and foundational work in the field, gives you a sense that you belong,” she says.
Night Sky With Milky Way
Night Sky With Milky Way
Legacy
Scientists still reference Payne-Gaposchkin’s thesis as they tackle some of the most pressing questions in astrophysics, such as: Are we alone in the universe?
Hinkel, who studies the relationships between stars and the planets orbiting them, cites Payne-Gaposchkin’s thesis in a 2024 study about how what stars are made of influences the composition of their planets. One goal of this line of research is to figure out which stars could host planets with the right conditions for life.
“It was really Cecilia Payne who started this field,” Hinkel says.
Since the 1990s, we have known that other stars besides our sun host planets, called exoplanets, and, more recently, that most stars in the Milky Way host at least one planet. But stars are much bigger and brighter than their planets, making stars easier to study. And while observatories in space and on the ground can give some clues about exoplanets, stars themselves are crucial to understanding these distant worlds.
While Payne-Gaposchkin broke the wisdom of her time that the sun should have the same chemistry as Earth, today astronomers know that elements present in stars do have some relationship to their planets. For example, the ratio of iron to magnesium in the sun resembles that of Earth and Mars, leading scientists to believe that some elemental ratios in stars reflect that of their planets.
Continuing Payne-Gaposchkin’s legacy of providing scientists with information about stars, Hinkel runs the Hypatia Catalog, a searchable repository of the known chemical compositions of more than 13,000 stars. She named it for the earliest known female astronomer, Hypatia of ancient Greece. Scientists can use this database as they explore which stars could host planets with ingredients and environments suitable for life.
Hinkel faced her own resistance in starting this catalog. Some fellow astronomers did not believe there needed to be a consistent database for stellar abundances. To this day, she takes inspiration from the perseverance of Payne-Gaposchkin and the other pioneering women of the Harvard College Observatory.
“When I’m struggling, I think back to, OK, you know, they dealt with it, they handled it,” she says. “I can deal with this, too, and I will figure out a way to get through it.”