Henrietta Leavitt discovers Cepheid variable stars, which serve as standard candles that can be used as cosmic distance benchmarks.
A photograph of Henrietta Leavitt at work.
Possibly Margaret Harwood via Harvard College Observatory
“150 Years Later, Her Star Is Still Rising: Henrietta Swan Leavitt’s Research at Harvard College Observatory Led to Two of the Most Important Discoveries in Astrophysics,” Harvard Gazette, 5 July 2018
Colleen Walsh, “Light Years Ahead: Star Analysts of Harvard College Observatory Struck Dava Sobel as Book-worthy History,” Harvard Gazette, 11 April 2017
Henrietta Leavitt, “1777 Variables in the Magellanic Clouds,” Annals of Harvard College Observatory, pages 87-108, 1908
Henrietta Leavitt, “Periods of 25 Variable Stars in the Small Magellanic Cloud,” Harvard College Observatory Circular, issue 173, 1912
Dava Sobel, The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars, 2016