Cecilia Helena Payne-Gaposchkin (May 10, 1900 – December 7, 1979) was a British-American astronomer and astrophysicist who, in 1925, proposed in her Ph.D. thesis an explanation for the composition of stars in terms of the relative abundances of hydrogen and helium.
Shapley persuaded Payne to write a doctoral dissertation, and so in 1925 she became the first person to earn a Ph.D. in astronomy from Radcliffe College (now part of Harvard). Her thesis was “Stellar Atmospheres, A Contribution to the Observational Study of High Temperature in the Reversing Layers of Stars”. Astronomer Otto Struve called it “undoubtedly the most brilliant Ph.D. thesis ever written in astronomy”.
Payne was able to accurately relate the spectral classes of stars to their actual temperatures by applying the ionization theory developed by Indian physicist Meghnad Saha. She showed that the great variation in stellar absorption lines was due to differing amounts of ionization at different temperatures, not to different amounts of elements. She correctly suggested that silicon, carbon, and other common metals seen in the Sun’s spectrum were found in about the same relative amounts as on Earth, but that helium and particularly hydrogen were vastly more abundant (for hydrogen, by a factor of about one million). Her thesis established that hydrogen was the overwhelming constituent of the stars (see Metallicity), and thus the most abundant element in the Universe.
When Payne’s dissertation was reviewed, astronomer Henry Norris Russell dissuaded her from concluding that the composition of the Sun is different from that of the Earth, contradicting the accepted wisdom at the time. However, he changed his mind four years later after deriving the same result by different means. After Payne was proven correct, Russell was often given the credit, although he himself acknowledged her work in his paper.
Cecilia Helena Payne was one of three children born in Wendover, England to Emma Leonora Helena (née Pertz) and Edward John Payne, a London barrister, historian and accomplished musician. Her mother came from a Prussian family and had two distinguished uncles, historian Georg Heinrich Pertz and the Swedenborgian writer James John Garth Wilkinson. Cecilia Payne’s father died when she was four years old, forcing her mother to raise the family on her own.
She attended St Paul’s Girls’ School. Her mother did not choose to spend money on her college education, but only on her brother’s. In 1919, she won a scholarship to Newnham College, Cambridge University, where she read botany, physics, and chemistry. Here, she attended a lecture by Arthur Eddington on his 1919 expedition to the island of Principe 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 Einstein‘s general theory of relativity. This sparked her interest in astronomy. She completed her studies, but was not awarded a degree because of her sex; Cambridge did not grant degrees to women until 1948.
Cecilia 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. After meeting Harlow Shapley, the Director of the Harvard College Observatory, who had just begun a graduate program in astronomy, she left England in 1923. This was made possible by a fellowship to encourage women to study at the Observatory. The first student on the fellowship was Adelaide Ames (1922) and the second was Payne.
After her doctorate, Payne studied stars of high luminosity in order to understand the structure of the Milky Way. Later she surveyed all the stars brighter than the tenth magnitude. She then studied variable stars, making over 1,250,000 observations with her assistants. This work later was extended to the Magellanic Clouds, adding a further 2,000,000 observations of variable stars. These data were used to determine the paths of stellar evolution. Her observations and analysis, with her husband, of variable stars laid the basis for all subsequent work on them.
Payne-Gaposchkin remained scientifically active throughout her life, spending her entire academic career at Harvard. At first, she had no official position, merely serving as a technical assistant to Shapley from 1927 to 1938. At one point she considered leaving Harvard because of her low status and poor salary. However, Shapley made efforts to improve her position, and in 1938 she was given the title of “Astronomer”. She later asked to have this title changed to Phillips Astronomer. None of the courses she taught at Harvard were recorded in the catalogue until 1945.
When Donald Menzel became Director of the Harvard College Observatory in 1954, he tried to improve her appointment, and in 1956 she became the first woman to be promoted to full professor from within the faculty at Harvard’s Faculty of Arts and Sciences. Later, with her appointment to the Chair of the Department of Astronomy, she also became the first woman to head a department at Harvard.
Her students included Helen Sawyer Hogg, Joseph Ashbrook, Frank Drake and Paul W. Hodge, who all made important contributions to astronomy. She also supervised Frank Kameny, who became a prominent advocate of gay rights.
Payne-Gaposchkin retired from active teaching in 1966 and was subsequently appointed Emeritus Professor of Harvard. She continued her research as a member of staff at the Smithsonian Astrophysical Observatory.