Cecilia Payne was the first female astronomer to be granted a professorship at Harvard and the first female department chair. Her doctoral thesis was a study on stellar spectra. Stellar spectra refers to the spectrum of colors of light reflected from stellar objects. By measuring the stellar spectra and comparing it to the light reflected from known elements, Payne was able to determine the chemical composition of the stars.
Cecilia Helena Payne Gaposchkin (1900-1979),
astrophysicist at Harvard College Observatory,
known for her research on stellar spectra.
Photo from Smithsonian Institution Archives
(Acc. 90-105 – Science Service, Records, 1920s-1970s)
Payne’s research was in direct conflict with the pre-eminent American physicists of her day. Geochemist Frank Wigglesworth Clarke had written a book comparing the strong spectral lines of the sun with his comprehensive sampling of minerals from the earth’s crust. Henry Norris Russell and Henry Rowland believed that the elemental abundances on the earth and in the Sun were nearly identical. Rowland’s opinion was because the spectra of the stars and the Sun were similar, that the relative abundance of elements in the universe was like that in the Earth’s crust.
Payne had a stronger knowledge of atomic spectra than most astronomers at the time and disagreed with Rowland. She applied research by Meghnad Saha that indicated temperature had a large effect on the atomic spectra. Payne used Saha’s equations to show that only one in 200 million of the hydrogen atoms in the Sun existed in the excited stat
e that gives off the signature spectra of hydrogen. As a result, she went on to show, the Sun as well as the stars were primarily formed of hydrogen and helium. The currently accepted values for elemental abundance in the Milky Way Galaxy (74% hydrogen, 24% helium, and 2% everything else) completely support her results.
Payne’s discovery brought a new view of the universe, much like the giants Copernicus, Newton, and Einstein. However, Payne was relatively unknown in the field. Many attribute this to the fact that she was a woman in the field at a time when women were denied many opportunities. Her obituary read in part, “Cecilia Helena Payne-Gaposchkin, a pioneering astrophysicist and probably the most eminent woman astronomer of all time, died in Cambridge, Massachusetts, on December 7, 1979. In the 1920s she derived the cosmic abundance of the elements from stellar spectra and demonstrated for the first time the chemical homogeneity of the universe.”