magnitude of the tenth brightest member

The magnitude of the tenth brightest member is a way of gauging the approximate distance to a cluster of galaxies that involves measuring the apparent magnitude of the cluster's tenth brightest member. The method is based on statistical studies, which show that clusters of galaxies tend to contain similar distributions of brighter and dimmer members. By assuming that the tenth brightest member of every cluster has the same brightness, and taking a standard value for the intrinsic brightness of this galaxy, the distance can be found.