Leavitt, Henrietta Swan

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Leavitt, Henrietta Swan (1868-1921), American astronomer, whose work made possible the first accurate determination of extragalactic distances. While working at the Harvard College Observatory on a survey of Cepheid variable stars (stars the luminosity, or brightness, of which varies in an extremely regular manner) she discovered (1912) that the Cepheids having the greatest average brightness also had the longest periods of variation. When, in 1913, the Danish astronomer Ejnar Hertzsprung accurately estimated the distances of a few Cepheids, the distances of all Cepheids could be calculated from Leavitt's period-luminosity correlation. This method of distance determination greatly increased the scientific knowledge of the physical universe.

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