The period-luminosity relationship for Cepheid variable stars, relating variability to absolute overall brightness, was discovered by
A) Harlow Shapley.
B) Henrietta Leavitt.
C) Edwin Hubble.
D) Sir Isaac Newton.

Question

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Henrietta Leavitt discovered the period-luminosity relationship for Cepheid variable stars, which is a fundamental method for measuring cosmic distances. This relationship shows that the intrinsic brightness of these stars is directly related to their variability period, allowing astronomers to use them as "standard candles" for measuring distances in the universe.

The Period-Luminosity Relationship for Cepheid Variable Stars, Relating Variability to Absolute