Henrietta Swan Leavitt dating history

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Henrietta Swan Leavitt (; July 4, 1868 – December 12, 1921) was an American astronomer. A graduate of Radcliffe College, she worked at the Harvard College Observatory as a "computer", tasked with examining photographic plates in order to measure and catalog the brightness of stars. This work led her to discover the relation between the luminosity and the period of Cepheid variables. Leavitt's discovery provided astronomers with the first "standard candle" with which to measure the distance to faraway galaxies. After her death, Edwin Hubble used Leavitt's period-luminosity relation, together with the galactic spectral shifts first measured by Vesto Slipher at Lowell Observatory, in order to establish that the universe is expanding (see Hubble's law). Before Leavitt noticed the relation between luminosity and the period which can be used for distances up to 20 million light years, astronomers relied on parallax and triangulation. The parallax and triangulation method works up to hundreds of light years, but not further. Our galaxy, the milky way, is already 100,000 light years big. Even further distances can be measured by using the theoretical maximum mass of white dwarfs calculated by Subrahmanyan Chandrasekhar.