American astronomer Henrietta Hill Swope was born #OTD in 1902.
Working with H. Shapley, she helped establish the famous period-luminosity relation for Cepheid variable stars, thereby permitting determination of the Sun's position in our galaxy and of distances to other galaxies. In 1962, using plates taken with the 200" Hale reflector by W. Baade, she determined the distance to the Andromeda galaxy to be 2.2 million light years.
en.wikipedia.org/wiki/Henriett…
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