Henrietta Hill Swope (October 26, 1902 – November 24, 1980) was an American astronomer who studied variable stars. In particular, she measured the period-luminosity relation for Cepheid stars, which are bright variable stars whose periods of variability relate directly to their intrinsic luminosities. Their measured periods can therefore be related to their distances and used to measure the size of the Milky Way and distances to other galaxies. Personal life She was the daughter of Mary Hill and Gerard Swope, and niece of Herbert Bayard Swope. Both of her parents taught at Hull-House in Chicago in the late 1890s, where they met. Her father had attended MIT and was an engineer. He worked for General Electric, eventually rising to be president of the company in 1922 and enabling his daughter to be independently wealthy throughout her life. She learned of talks at Maria Mitchell Observatory while vacationing with her family on Nantucket, and took an evening class there alongside her brother. She also heard Harvard astronomer Harlow Shapley speak; eventually she would go to work with him on variable stars. Education Swope attended Barnard College, and graduated in 1925, with an AB degree in mathematics. She only took an astronomy class, from Harold Jacoby, in her final year. After college, she went back to Chicago and attended the School of Social Service Administration, at the University of Chicago, but only for one year. While working with Harlow Shapley, she obtained her Masters in Astronomy in 1928 from Radcliffe College. Professional history She learned that Dr. Shapley at Harvard was offering fellowships for women to work on finding variable stars. Swope went to work for Shapley in 1926 and began working alongside other "girls" to identify variable stars in the Milky Way. She became friends with Cecilia Payne-Gaposchkin and Adelaide Ames. She supported herself on a salary from Harvard and a stipend from her family. She became an expert on estimating magnitudes of stars from images on photographic plates. Swope left Harvard to work for MIT's staff radiation laboratory in 1942. In her Oral History, she says, "...they said, 'How much were you getting [at Harvard]?' And I said, I think, $2000. That’s what they say they would pay me, what I was getting, but that was too little for them. They couldn't. So I rose fairly quickly." From 1942-1947, she worked on the LORAN navigation tables. From 1947 until 1952,