The brightest star, arbitrarily defined as the mean of the three or four brightest individual, non-variable stars in a nebula, is calibrated as a criterion of distance (M8 = 6.35, Os =0.41). The luminosity function of resolved nebulae is then derived from the frequency distribution of m8 -inn, which measures the luminosity of a nebula in terms of its bright- est star as the unit. The luminosity function approximates a normal error-curve with Mon=I4.2±,~n=o.85,andMn=-I5.I8. Incomplete data for brightest stars in members of the Virgo cluster suggest a modu- lus, m-M, of 26.6 or slightly larger. Cluster members are roughly comparable with resolved field nebulae, and, within the cluster, different types of nebulae are comparable among themselves
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Edwin Hubble (1936) studied this question.