Today is the birthday of astronomer Cecilia Payne-Gaposchkin, born in Wendover, England, in 1900. Payne went to the University of Cambridge to study botany but was captivated by a public lecture by Arthur Eddington, the astronomer who observed the 1919 solar eclipse that confirmed Einstein's general theory of relativity. She switched her focus to physics and then astronomy. Realizing the limited opportunities for female scientists in England, Payne accepted a graduate fellowship at Harvard College Observatory. There she studied stellar spectra, analyzing the light from stars to deduce their chemical composition and other properties. At the time researchers had classified stars into several categories based on their spectra. Many astronomers suspected that stars had largely the same composition as Earth but differed in their surface temperature, which led to the varying spectra. In her PhD thesis, Payne quantified the different surface temperatures of the stellar classes. But the spectra also led her to a startling conclusion: Stars are made almost entirely of hydrogen and helium. It took several years for astronomers to embrace that aspect of her thesis, which a pair of prominent astronomers later called "undoubtedly the most brilliant PhD thesis every written in astronomy." Payne's insight has become a central tenet of astronomy and astrophysics: The universe is awash in hydrogen, with stars and explosions such as supernovas responsible for creating heavier elements. Later in her career Payne turned her attention to variable stars that ebb and flow in brightness. In 1956, after decades as one of the world's leading astronomers, Harvard finally made her a full professor, the first woman to attain that title at the school. To learn more about this pioneering scientist, check out this interview conducted in 1968 and archived by the Center for History of Physics/Niels Bohr Library & Archives: https://goo.gl/3LY9OG. There's also an audio clip.
