Trumpler's classification

Trumpler's classification

(trump -lerz) A method of classifying open clusters according to their appearance, using the three criteria of stellar concentration toward the center, range in brightness of the member stars, and the total number of stars in the cluster. The method was devised by the Swiss-American astronomer Robert Trumpler, who also found a correlation between this appearance classification and the cluster diameter.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006