What fundamental relationship did Henrietta Leavitt discover regarding Cepheid variable stars?

Answer

The pulsation period is directly related to the star's true average luminosity.

Henrietta Leavitt established that the time it takes for a Cepheid variable star to pulse (its period) dictates how intrinsically bright the star truly is; a longer period means greater average luminosity.

What fundamental relationship did Henrietta Leavitt discover regarding Cepheid variable stars?

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