The Cecilia Helena Payne

Is said to be the “most eminent woman astrophysicist of all time”. She was one of the only women in a field greatly dominated by men. However, she did not let this stop her from pursuing her dreams in becoming an astrophysicist. She faced a few challenges because she was a woman, but she made some of the most important discoveries in astronomy. Her breakthroughs are still used to this day, one hundred years later. Payne grew up in a family that was well educated. Her father was a lawyer, musician and a scholar but died when she was four. In 1919, she attended Cambridge where she studied botany, physics and chemistry. Eventually the botany aspect dropped out, but the taxonomy aspect from biology stayed with her and created a passion inside of her.

She became a “relentless classifier of variable stars”. Payne’s passions turned greatly towards physics and that was when she attended a lecture by Arthur Eddington, which turned her interests to astronomy. She was encouraged to go to Harvard for a fellowship to study astronomy. As a woman, she realized that she would not have as many opportunities in England as she would in America. She arrived at Harvard in the fall of 1923 and by 1924 she had taken a preliminary general examination for her PhD. From her background at Cambridge, it only makes sense that she went on to work in the astrophysics field. In the early 1920’s, one of the main questions posed for astrophysicists was relating to the photographic stellar spectra collections.

Payne came to a solution for tables correlating spectral type with surface temperature.  At that time, Harvard had one of the biggest collections of stellar spectra on photographic plates. Before Payne’s organizational scheme, astronomers figured the different spectral classes were related to a decrease in surface temperature, but no one had a way to show it. Payne knew that the spectrum of atoms is due to the configuration of its electrons and that at higher temperatures electrons can be taken away from atoms and then they are called ions. She used the ionization theory from Meghnad Saha to relate the spectral classes of stars to their temperatures.

Saha had found that temperature and the pressure of the atmosphere around a star can show the degree of how atoms are ionized. Payne was able to show that the vast difference between absorption lines was actually because of the different amounts of ionization at different temperatures and not because of the different amounts of each element. She used Saha’s equilibrium equation to “relate ratios of excited states to ground states, and the fraction of ionized states to the temperature, electron concentration, ionization potential and other properties of the stellar atmosphere”. At the time, it was believed that the atmospheres of the Sun and stars was the same as that of the Earth’s.

Originally, it was believed that you could figure out what stars are made out of by comparing the spectral lines to elements previously found. Previous astronomers had discovered iron and calcium to be more abundant on Earth and assumed that these elements also made up the stars. At the time, the density of the Earth could be explained by a heavy iron core. This along with meteorites from outer space, led astronomers to believe iron was extremely abundant in atmospheres of stars. However, she discovered that hydrogen and helium were the most abundant instead of other heavier elements. She found that hydrogen was the most abundant with helium in second place, with iron to be a very small amount of the composition.

She was seen as the Copernicus of her time, with her findings of hydrogen and helium being the prominent elements instead of what made up the Earth’s atmosphere being as controversial as the Sun being the center of the solar system. Her findings were not well received by other astrophysicists. Historian David DeVorkin stated, “The possibility that hydrogen was the primary constituent of the universe was not a welcoming thought at all. Even though hydrogen was the most persistent line feature in the spectra of the stars, and sometimes the most prominent, astronomers felt strongly that it could not be a major constituent of the stars,”. After being told this discovery must be incorrect, she did not publish it boldly. She kept trying to find the error in her work, so she kept re-checking her results.

But, through the following decade, there were other findings that proved the Earth’s makeup is very different than other objects in the solar system, thus confirming what Payne had previously found. After she married Gaposchkin, who was a Russian astronomer, they studied variable stars, the structure of the Milky Way and other galaxies that are nearby, such as the Magellanic Clouds. During the 1930’s -1940’s, Payne, her husband, and twenty-nine assistants made more than 1,250,000 measurements of stars on the Harvard photographic plates. They measured the variable stars of the Magellanic Clouds by looking at their visual magnitudes. Payne procured periods for over 3000 of them.

In 1974, she stated that the Cepheid variable stars with the longest periods are the youngest stars and are concentrated at the northern side of the Magellanic Cloud. Their method for categorizing stars, Variable Stars, became the standard reference. Payne ended up making her thesis into a book called Stellar Atmospheres. She had also written six papers by the time she finished her PhD. From 1923 to 1942, Payne was an author or coauthor on an astounding seventy-eight papers that were related to analyzing stellar spectra. In 1926, she was the youngest person to ever been in American Men of Science. She was appointed to the Commission on Spectral Classification and was a member in the International Astronomical Union. In 1976, she was awarded the Henry Norris Russel Prize by the American Astronomical Society. In her entire lifetime, she wrote over 150 papers, multiple monographs, and four books on stars and stellar evolution.

One of the problems she faced as a woman in the field of astronomy, was that when the time came to find teachers for the Harvard graduate department, she was overlooked. She was kept in a research position where she continued to work on stellar photometry. She did have lectures at the observatory but were kept off the catalog until 1945. That is when she became the first woman to become a professor to receive a tenure at Harvard and become the department chairman, which was also a first. When she was publishing her dissertation, Stellar Atmospheres, she was encouraged to make her statement more ambiguous and so she altered them and never received credit. She was told this by Henry Norris Russell, who was an astronomer at Princeton. However, a few years later he came to the same conclusions and Payne and published his work. He is the one who received credit for this discovery.

Cecilia Payne made a revolutionary discovery. She was able to find the true composition of the Sun and the stars as well as come up with the way to classify them. She took a previous belief of the Sun and stars being made up of heavy elements like the Earth, are mainly made up of two of the lightest elements. She was able to answer one of the oldest questions people had, she was able to determine what stars were made of, and how to categorize them. She paved the way for many more bright, young female astrophysicists. She was able to challenge beliefs that had been held by her colleagues and show she was right. “There is no joy more intense than that of coming upon a fact that cannot be understood in terms of currently accepted ideas.”