why are pulsating variable stars useful for finding distance to globular clusters
He used the inverse square law of light brightness on a particular type of variable star in those old star clusters. Some stars are very useful for finding distances to clusters and to other galaxies because they have a known luminosity that is large, so they can be seen from great distances away.ll of the RR Lyrae stars in a cluster have the same average apparent magnitude. In different clusters, the average apparent magnitude was different. This is because all RR Lyrae have about the same average absolute magnitude (=+0.6, or 49 solar luminosities).