Cecilia Payne-Gaposchkin (born Cecilia Helena Payne; (1900-05-10)May 10, 1900 – (1979-12-07)December 7, 1979) was a British-born American astronomer and astrophysicist. Her work on the cosmic makeup of the universe and the nature of variable stars was foundational to modern astrophysics.
She determined that stars were composed primarily of hydrogen and helium in her 1925 doctoral thesis. Her groundbreaking conclusion was initially rejected by leading astrophysicists, including Henry Norris Russell, because it contradicted the science of the time, which held that no significant elemental differences distinguished the Sun and Earth. Independent observations eventually proved that she was correct.
Despite completing her studies, because she was a woman Payne was not eligible to receive a degree from the University of Cambridge. Similarly in America, she was not eligible to receive a doctoral degree (PhD) for her studies at Harvard University, as the university did not grant doctoral degrees to women at the time. Instead, she received her doctoral degree from Radcliffe College – a liberal arts college for women that began as a study program for women within Harvard. She would go on to overcome barriers for women that she encountered in science and her success opened the door for countless women astronomers, including her Harvard colleague, Helen Sawyer Hogg.
While she was a student at Cambridge, Payne was elected to the Royal Astronomical Society. Later, she became the first recipient of the American Astronomical Society’s prestigious Annie Jump Cannon Award in Astronomy. In 1956, she was the first woman appointed as a professor and as a department chair at Harvard.
Her work resulted in several published books, including The Stars of High Luminosity (1930), Variable Stars (1938), and Variable Stars and Galactic Structure (1954).
Cecilia Helena Payne, born in Wendover in Buckinghamshire, England, was one of three children born to Emma Leonora Helena (née Pertz), from an erudite Prussian family, and Edward John Payne, a London barrister. Her father was a historian and musician who had been an Oxford fellow. Payne had two distinguished uncles, historian Georg Heinrich Pertz and the Swedenborgian writer James John Garth Wilkinson. When Cecilia was four, her father died, leaving her mother to raise the family on her own.
Payne began her formal education in Wendover at a private school run by Elizabeth Edwards. When Payne was twelve, her family moved to London to facilitate the education of her brother, Humfry; he later became an archaeologist. Payne initially attended St. Mary's College, Paddington, where study of mathematics or science was not available to her. In 1918, she transferred to St. Paul's Girls' School, where her music teacher, Gustav Holst, encouraged her to pursue a career in music. However, Payne decided to focus on science. The following year she won a scholarship covering her expenses at Newnham College, Cambridge University, where she studied physics and chemistry.
Her interest in astronomy began after she attended a lecture by Arthur Eddington, detailing his 1919 expedition to the island of Príncipe in the Gulf of Guinea off the west coast of Africa to observe and photograph the stars near a solar eclipse as a test of Albert Einstein's general theory of relativity. She said of the lecture: "The result was a complete transformation of my world picture. [...] My world had been so shaken that I experienced something very like a nervous breakdown." Although she completed her studies, she did not receive an official degree because Cambridge did not grant degrees to women until 1948.
Payne realized that her only career option in the U.K. was to become a teacher, so she looked for grants that would enable her to move to the United States. Leslie Comrie, then a PhD student at Cambridge University, introduced her to Harlow Shapley, the director of the Harvard College Observatory, after a lecture in London at the British Astronomical Association. A fellowship established to encourage women to study at the Harvard Observatory enabled Payne to move to the United States to study at Harvard College in 1923. Adelaide Ames had been the first recipient of this fellowship in 1922, with Payne following as the second.
Lawrence H. Aller later described Payne as one of the "most capable go-getters" in Shapley's observatory. She then studied related courses at Harvard via the program for women and Shapley persuaded Payne to write a doctoral dissertation on a topic in astronomy.
In 1925, Payne became the first person to earn a doctoral degree (PhD) in astronomy from Radcliffe College of Harvard University. Her thesis was Stellar Atmospheres; A Contribution to the Observational Study of High Temperature in the Reversing Layers of Stars.
While analyzing glass plates at the Harvard College Observatory, Payne made a groundbreaking discovery by accurately relating the spectral classes of stars to their measured temperatures using Indian physicist Meghnad Saha's ionization theory. She demonstrated that the great variation in stellar absorption lines was due to differing amounts of ionization at different temperatures, not to varying amounts of elements. Payne found that silicon, carbon, and several common metals seen in the Sun's spectrum were present in about the same relative amounts as on Earth, which aligned with the prevailing belief that stars had a similar elemental composition as on Earth, however, she found that helium, and particularly hydrogen, were vastly more abundant in stars, with hydrogen being about a million times more prevalent. This discovery was the basis of her conclusion that hydrogen was the overwhelming constituent of stars, making it the most abundant element in the Universe.
During the review process of Payne's dissertation, Henry Norris Russell, a pre-eminent astronomer of the day who adhered to the theories of American physicist Henry Rowland, urged her not to assert that the composition of the Sun was predominantly hydrogen, however, because it contradicted the scientific consensus of the time that the elemental composition of the Sun and the Earth were similar. Russell, in a 1914 article, had argued that:
The agreement of the solar and terrestrial lists is such as to confirm very strongly Rowland's opinion that, if the Earth's crust should be raised to the temperature of the Sun's atmosphere, it would give a very similar absorption spectrum. The spectra of the Sun and other stars were similar, so it appeared that the relative abundance of elements in the universe was like that in Earth's crust.
Consequently, Russell described her scientific conclusion as "spurious". Although she included all calculations and results, Payne accommodated the criticism of her reviewer by including a statement in her thesis that her results were "almost certainly not real".
Four years later, however, Russell realized that Payne had been correct when he derived the same results by different means, effectively demonstrating that hydrogen and helium were the most abundant elements in the Milky Way, just as Payne had concluded in her thesis. Sharing his results professionally in 1929, Russell briefly acknowledged Payne's earlier work and discovery, including the mention that "[t]he most important previous determination of the abundance of the elements by astrophysical means is that by Miss Payne [...]", yet Russell was generally credited for the conclusions Payne had reached four years prior.
Nearly 40 years after Payne's thesis was published, professional recognition of her discovery was given to her by astronomer Otto Struve when he described her work as "the most brilliant PhD thesis ever written in astronomy". Today's accepted ratios for hydrogen and helium in the Milky Way Galaxy are ~74% hydrogen and ~24% helium, confirming the results of Payne-Gaposchkin's calculations from 1925.
Her work also resulted in several published books, including The Stars of High Luminosity (1930), Variable Stars (1938), and Variable Stars and Galactic Structure (1954).