Passage II

Cecilia Payne-Gaposchkin and Star Composition

In 1923, when Cecilia Payne-Gaposchkin arrived in the United States to study astronomy, however, a widely held belief in her chosen field was that the stars, including the Sun, varied widely in its composition. Her PhD thesis, published in 1925, asserting that, unlike the planets, all stars are largely composed of hydrogen and helium. The idea instantly met with vehement opposition from her colleagues.

[1] Within a few years, however, studies by other astronomers, Otto Struve in particular went on to prove that Payne-Gapuschkin's assertion was correct. [2] Payne-Gaposchkin eventually published more than 150 papers and monographs and rose to be the first woman to chair a department at Harvard University. [3] Struve, in fact, said that her work was "the most brilliant thesis ever written in astronomy." (22)

To accomplish the groundbreaking work of her thesis, published in 1925, Payne-Gaposchkin had applied astrophysicist Meghnad Saha's newly developed theory of ionization to the study of stellar atmospheres. [A] She labored by what was at the time the world's largest collection of stellar spectra on photographic plates in the world. To the untrained eye, stellar spectra look like random smears on a sheet of paper. The images that were created with a spectroscope, an instrument that, when attached to a telescope, captures the various wavelengths of starlight on a color spectrum. [B] Payne Gaposchkin turned most of her attention to the"absorption lines," the dark gaps where light at certain wavelengths was missing. [C] She concluded, ultimately that the variations among stellar spectra were not, as previously thought, an indication of different stellar composition. [D] Instead, she took the position that the gaps could be attributed to the different temperatures of stars but that the stars' elemental makeup was largely uniform. The discovery is, to this day, considered one of the greatest in the field of astronomy. (30)