The concept that allowed Hubble to determine a star's actual energy output (absolute magnitude) using its pulsation cycle is known by what term?

Answer

Period-Luminosity graph

Hubble used the Period-Luminosity graph, derived from nearby Cepheids whose distances were known via parallax, to convert V1's measured period into its actual energy output (absolute magnitude).

The concept that allowed Hubble to determine a star's actual energy output (absolute magnitude) using its pulsation cycle is known by what term?
measurementgalaxyAstronomerDistancecalculation