Open Clusters in the log Age vs. M_V plane

We introduce the log Age vs. integrated absolute magnitude (M_V) plane as a diagnostic plane to compare different classes of star clusters and/or star cluster populations of different galaxies. In this plane, the open clusters of the Milky Way form a well-defined band parallel to theoretical sequences decribing the passive evolution of Simple Stellar Populations and display a pretty sharp upper threshold in mass (M ~ 2X 10^4 M_{sun}) over a 4 dex range of ages.