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Cecilia Payne-Gaposchkin, a Giant of Physics

posted by Jason Kottke   Dec 17, 2019

Prompted by this Facebook post, I have been reading about astrophysicist Cecilia Payne-Gaposchkin, who should be more widely known than she is. From a piece last year in Cosmos:

Cecilia Payne, born on May 10, 1900, in Wendover, England, began her scientific career in 1919 with a scholarship to Cambridge University, where she studied physics. But in 1923 she received a fellowship to move to the United States and study astronomy at Harvard. Her 1925 thesis, Stellar Atmospheres, was described at the time by renowned Russian-American astronomer Otto Struve as “the most brilliant PhD thesis ever written in astronomy”.

In the January, 2015, Richard Williams of the American Physical Society, wrote: “By calculating the abundance of chemical elements from stellar spectra, her work began a revolution in astrophysics.”

Even though she completed her studies at Cambridge, she was not awarded a degree because the university did not give degrees to women. That’s when she decided to move to the US, where Harvard offered greater educational opportunities and a “collection of several hundred thousand glass photographs of the night sky” that Payne-Gaposchkin was uniquely qualified to analyze.

Miss Payne applied the new theories of atomic structure and quantum physics to her analysis of stellar spectra. No one at the Harvard Observatory had yet attempted such an investigation, as no one there possessed the necessary background. She, in contrast, had learned the complex architecture of the “Bohr atom” directly from Niels Bohr, winner of the 1922 Nobel Prize in physics. She had also followed the work of Indian physicist Meg Nad Saha of Calcutta, the first person to link the atom to the stars. Saha maintained that the line patterns in stellar spectra differed according to the temperatures of the stars. The hotter the star, the more readily the electrons of its atoms leaped to higher orbits. With sufficient heat, the outermost electrons broke free, leaving behind positively charged ions with altered spectral signatures.

Building on Saha’s base, with insights gained from a couple of her professors in England, Miss Payne selected specific spectral lines to examine. Then she estimated their intensities in hundreds of stellar spectra. Element by element she gauged, plotted, and calculated her way through the plates to take the temperatures of the stars.

Her groundbreaking work on spectra, laid out in her Ph.D thesis published when she was just 25, puts Payne-Gaposchkin in the same league as some other physics heavy hitters.

Her discovery of the true cosmic abundance of the elements profoundly changed what we know about the universe. The giants — Copernicus, Newton, and Einstein — each in his turn, brought a new view of the universe. Payne’s discovery of the cosmic abundance of the elements did no less.