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Leavitt's yardstick
Leavitt was one of the Harvard Computers, a group of women employed to measure and catalogue plates at far lower pay than men, and without access to the telescope. The period–luminosity relation she found in Cepheid variables underlies the entire cosmic distance ladder: Hubble used it in 1924 to show that Andromeda lies outside the Milky Way, and in 1929 to show that the universe is expanding. She died of cancer in 1921. A Swedish mathematician tried to nominate her for the Nobel Prize in 1925 and was told she was dead — the prize is not awarded posthumously.
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