British-American astrophysicist Cecilia Payne-Gaposchkin (1900–1979) conducted scientific research that led her to the discovery of the composition of stars. In 1956, amid a stellar career, Payne-Gaposchkin was recognized among the pioneering astronomers of her generation and became the first woman appointed a full professor at Harvard University.
In the early part of the 20th century, scientists were increasing humankind's knowledge about both their inner world and the space that surrounded their planet. As discoveries were made in the areas of physics, earth science, and astronomy, the literate general public became aware of the limits of human knowledge and of the many questions still to be asked. Among the most compelling of these unanswered questions concerned the night sky, a subject of perennial fascination: What exactly is a star and what is it composed of? British-born astrophysicist Cecilia Payne-Gaposchkin worked almost obsessively on the star question and answered it. PayneGaposchkin made her groundbreaking discovery when she was only 25 years old.
In 1925, Payne-Gaposchkin's research became her Ph.D. thesis at Harvard University Observatory in Harvard, Massachusetts. Not only did her work provide more knowledge about the universe, it also was important in the development of the study of stellar atmospheres. Looking back on Payne-Gaposchkin's published Ph.D., distinguished U.S. astronomer coauthors Otto Struve and Velta Zebergs would deem it “the most brilliant Ph.D. thesis ever written in astronomy” in their Astronomy of the 20th Century.
Cecilia Helena Payne was born May 10, 1900 in Wendover, England. She was one of three children born in a family known for its intellectual interests, heritage and connections. PayneGaposchkin's father, Edward John Payne, was an historian, a talented musician, and a barrister (lawyer) with offices in London; her mother, Emma Leonora Helena, was of Prussian extraction. Most of Payne-Gaposchkin's upbringing was done by her mother, as her father died when she was four years old. Uncles influencing her intellectual bent included noted historian Georg Heinrich Pertz and famous writer James John Garth Wilkinson. Her family cherished a box of family letters that included signed papers of both Charles Darwin (1809–1882), the naturalist made famous for his work on the theory of evolution, and Charles Lyell (1797–1875), a renowned geologist and the author of the groundbreaking Principles of Geography. Payne-Gaposchkin eventually inherited this box of notable documents and it may have served an inspiration.
Payne-Gaposchkin benefitted from a quality education and in 1919 she won a scholarship to Newham College Cambridge. At Newham, she became interested in science and studied botany, physics, and chemistry. Her interest turned to astronomy upon attending a lecture by astronomer Sir Arthur Eddington (1882–1944). After listening to Eddington's lecture, she returned to her dormitory room and transcribed the lecture from memory. By this time, Payne-Gaposchkin had decided to major in physics at Newham College, but Eddington talk inspired her to shift her focus to astronomy. Unfortunately, this was not possible because, at the time, astronomy was considered a branch of mathematics, not physics.
While studying physics, Payne-Gaposchkin attended other lectures given by Eddington and one point she spoke to him, explaining that she wanted to become an astronomer. Noting that he did not see any obstacle to this goal, Eddington suggested that she read certain books if she was indeed serious about studying astronomy. Much to his surprise, Payne-Gaposchkin told the professor that she had already read all of the texts he suggested. PayneGaposchkin was proving herself a woman of substantial intellectual capacity.
After completing her studies at the University of Cambridge (which would not grant degrees to women until 1948), Payne-Gaposchkin realized that England would be a difficult place for a woman wishing to pursue a career in astronomy; teaching would be her only option. In the United States, female astronomers appeared to be more accepted, and an introduction to the director of the Harvard College Observatory proved timely. In 1923, she moved to the United States, the recipient of a graduate fellowship at the observatory. Located in Cambridge, near Boston, Massachusetts, the observatory provided her with a fine environment for research, as it owned the world's largest archive of stellar spectra, light characteristics captured on photographic plates. Astronomers made these plates by using a telescope attached with a spectroscope (an instrument that measures light properties over a specific part of the electromagnetic spectrum). That technological coupling resulted quantifiable information about the colors and wavelengths of starlight.
During the late 1880s, the study of stellar spectra had led to the development of the science of astrophysics, which married two of Payne-Gaposchkin's major interests: physics and astronomy. The new science was moved forward by Gustav Kirchoff (1824–1887) and Robert Bunsen (1811–1899), both based in Germany, and William Huggins (1824–1910), an Englishman. Together and separately, these men studied laboratory spectra and spectral lines and discovered that the visible universe is made of the same chemical elements found on Earth. Elements such as calcium and iron had some of the most prominent spectral lines and these types of heavy elements proved to be some of the major constituents of stars. Working along the same research lines at Princeton University, Henry Norris Russell (1877–1957) concluded that if Earth's crust were increased to the temperature of the Sun, its color spectrum would look nearly the same.
By the time Payne-Gaposchkin began her tenure at Harvard College Observatory, an ongoing, comprehensive study of stellar spectra had already begun. Annie Jump Cannon (1863–1941) had sorted the spectra of several hundred thousand stars into seven classes, basing her classification stratagem on differences in spectral features. A question remained, however. Astronomers assumed that the spectral classes represented a sequence of decreasing surface temperatures of stars, but this assumption had not been quantitatively demonstrated.
Payne-Gaposchkin was now intellectually equipped and ready to start a long project and she decided that she would measure absorption lines in stellar spectra. Through her work, she established a correlation between the patterns of features in the spectrum of any atom and that atom's electron configuration. She also knew that high temperatures take away one or more electrons from atoms. These separated electrons are called ions.
Two years later, in 1925, Payne-Gaposchkin presented her findings as part of her doctoral thesis. In this document she demonstrated that the wide variation in stellar spectra is due mainly to the different ionization states of the atoms and the different surface temperatures of the stars. Her conclusion was achieved by calculating the relative amounts of 18 elements and learning that the compositions of different types of stars were quite similar. A surprising discovery involved hydrogen and helium, two of the lightest elements, which Payne-Gaposchkin found accounted for 99 percent of a star's mass. Heavier elements, such as those found on Earth, made up only two percent of a star's mass. This discovery, that hydrogen was the primary component of the sun, the largest star, went against what scientists had assumed.
In 1925 Payne-Gaposchkin was the first Ph.D. graduate in astronomy at Radcliffe College (the women's college affiliated with all-male Harvard College). More significantly, her research made it possible to read the surfaces temperature of a specific star from the rainbowlike band of colors in its stellar spectrum. It also enabled scientists to calculate stellar temperatures and to accurately interpret the Hertzsprung-Russell diagram, which plotted luminosity against the spectral class of the stars. This diagram now became the most powerful tool for astrophysicists engaged in analysis.
Following completion of her fellowship and publication of her first dissertation, Payne-Gaposchkin was asked to join the staff at Harvard College Observatory, serving Shapley as an assistant and working with other female astronomers. In 1932, she toured Europe and visited other observatories. In Berlin, Germany, to attend a meeting of the Astronomische Gesellschaft, an astronomical society established in 1863, she met the man who would become her husband, Sergei Gaposchkin (1889–1984), a young Russian astronomer who lived in Germany at the time. Now ruled by a government based in the city of Weimar, Germany was the site of political foment due to rising inflation, social unrest, and the competing interests of communists and the socialist Nazi party. Although Gaposchkin had been forbidden to leave by authorities, Payne-Gaposchkin helped him emigrate from Europe and also found him a position at Harvard when he arrived in November 1932. In March 1934, the couple were married and they formed an effective team, conducting work on the physical understanding of variable stars.
Although Payne-Gaposchkin worked as a professor at Harvard throughout the 1930s, her title remained that of technical assistant; a subtitle of Astronomer was added in 1938 when she threatened to leave the college. Under a new director, in 1956, she was named full professor (the first woman at Harvard to earn that title) as well as chairperson of the astronomy department. Inducted into the American Philosophical Society in 1936 and the American Academy of Arts and Sciences in 1943, PayneGaposchkin eventually, in 1976, received the prestigious Henry Russell Prize from the American Astronomical Society, a recognition previously denied her because of her gender. She also published several books, among them Variable Stars (1938), Stars in the Making (1952), Variable Stars and Galactic Structures (1954), The Galactic Novae (1957), and Stars and Clusters (1979).
Payne-Gaposchkin died in Cambridge, Massachusetts on December 7, 1979. Her obituary in the Quarterly Journal of the Royal Astronomical Society described her as “a pioneering astrophysicist and probably the most eminent woman astronomer of all time.” She shared her reflections in Cecilia Payne-Gaposchkin: An Autobiography and Other Recollections, a work edited by her daughter, Katherine Haramundanis, and published in 1984.
Payne-Gaposchkin, Cecilia, Cecilia Payne-Gaposchkin: An Autobiography and Other Recollections, Cambridge University Press, 1984.
Soter, S., and Neil deGrasse Tyson, editors, Cosmic Horizons: Astronomy at the Cutting Edge, New Press, 2000.
Struve, Otto, and Velta Zebergs, Astronomy of the 20th Century, Macmillan, 1962.
Quarterly Journal of the Royal Astronomical Society, Volume 23, 1982.
American Physical Society website website, https://www.aps.org/ (October 20, 2016), Richard Williams, “January 1, 1925: The Day the Universe Changed.”
Contributions of 20th Century Women to Physics website/University of California, Los Angeles, http://cwp.library.ucla.edu/ (October 20, 2016), “Cecilia Helena Payne Gaposchkin.”
Goodsell Observatory website, https://apps.carleton.edu/ (October 20, 2016), “Cecilia Helena Payne-Gaposchkin.”❑