Henrietta Leavitt (1868-1921). American astronomer who, working as a "computer" at the Harvard College Observatory cataloging photographic plates of the night sky for thirty cents an hour, discovered the period-luminosity relation in Cepheid variable stars — the discovery that made measuring distances to other galaxies possible, and consequently made modern cosmology possible. Hubble used Leavitt's relation to determine that the Andromeda galaxy was outside the Milky Way, fundamentally changing our picture of the universe's scale. Leavitt's cognitive signature is the discovery specialty operating inside a credentialing apparatus designed to use her output without recognizing her contribution: monotropic visual pattern-extraction sustained over years of looking at photographic plates, identification of a periodic regularity nobody else had noticed, and complete indifference to whether the discovery would carry her name. She was deaf for most of her career. She was never admitted to the meetings of the (male) astronomers who used her work. She died at fifty-three before the full implications of her discovery were widely understood. Mittag-Leffler nominated her for the Nobel Prize three years after her death, not knowing she had already died.