main-sequence fitting

main-sequence fitting

A technique for measuring the distance modulus and hence distance for a star cluster, especially an open cluster: the main-sequence portion of a graph of color index versus apparent magnitude for the cluster is superimposed on the main sequence of a Hertzsprung–Russell diagram, the color indices of the two curves being made to overlap. The difference between cluster magnitudes and the superimposed absolute magnitudes of the H-R diagram is approximately constant and equal to the distance modulus.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006