What fundamental law established by Henrietta Swan Leavitt links Cepheid period to brightness?
Answer
Period-Luminosity Relationship
The Period-Luminosity Relationship is the fundamental law discovered by Henrietta Swan Leavitt that governs Cepheid variables. This relationship states there is a direct correlation between how long a Cepheid takes to complete one cycle of brightening and dimming (its period) and its true, intrinsic brightness (its absolute magnitude). Specifically, the longer the period, the more luminous the star inherently is. This mathematically reliable link transformed the Cepheid from a mere curiosity into the primary tool for measuring cosmic distances, enabling its function as a standard candle.
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