Which scientist established the fundamental relationship used by Hubble to determine the true luminosity of Cepheid variable stars?

Answer

Henrietta Swan Leavitt

Henrietta Swan Leavitt had previously established that the period of a Cepheid star's pulsation is directly related to its true luminosity, which was essential data for Hubble's distance calculations.

Which scientist established the fundamental relationship used by Hubble to determine the true luminosity of Cepheid variable stars?
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