Period-luminosity relation

The period-luminosity relation is a discovery in astronomy that shows a direct link between the brightness of certain variable stars, called Cepheids, and how long they take to pulsate. Specifically, brighter Cepheids have longer pulsation periods. This means by measuring how long a Cepheid takes to brighten and dim, astronomers can determine its true brightness. Comparing this with its observed brightness from Earth allows them to calculate its distance. This relation is a crucial tool for measuring how far away distant galaxies and stars are in the universe.