what makes cepheid variable stars useful in determining star distances
Cepheid variable A strong direct relationship between a Cepheid variable's luminosity and pulsation period[1][2] established Cepheids as important indicators of cosmic benchmarks for scaling galactic and extragalactic distances.[3][4][5][6] This robust characteristic of classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt after studying thousands of variable stars in the Magellanic Clouds.[7] This discovery allows one to know the true luminosity of a Cepheid by simply observing its pulsation period. This in turn allows one to determine the distance to the star, by comparing its known luminosity to its observed brightness.