Shapley–Sawyer Concentration Class

The Shapley - Sawyer concentration classes form a qualitative classification system, with the Harlow Shapley and his doctoral student Helen Sawyer Hogg arranged on photographic images according to their apparent concentration from 1927 globular clusters. The scale ranges from one to twelve, with Roman numerals are used. The most concentrated clusters are in Class I, such as M75. With decreasing concentration the class number increases and reaches up to class XII, such as in NGC 4372nd The class boundaries were set by Shapley and Sawyer Hogg so that the twelve classes each about contained the same number of known 1927 95 globular clusters. The brightest clusters in the northern sky ( Messier 13) belongs to the class V.

The concentration classes are still used today, for example, by amateur astronomers to describe the expected appearance in mixed observation of globular clusters. For scientific purposes quantitative measures to describe the structure of the clusters are to be preferred, how to get them to the measured surface brightness profiles by fitting parametric models about.

Swell

• Star clusters