Shapley-Sawyer concentration class
The Shapley Sawyer concentration classes form a quality classification system , with the Harlow Shapley and his doctoral Helen Sawyer Hogg 1927 globular clusters on photographic recordings according to their apparent concentration arranged.
The scale ranges from one to twelve, using Roman numerals :
- The most concentrated clusters are assigned to class I, e.g. B. M75 .
- With decreasing concentration, the class number increases and extends up to class XII, e.g. B. at NGC 4372 .
- The class boundaries were set by Shapley and Sawyer Hogg so that the twelve classes each contained approximately the same number of the 95 globular clusters known in 1927.
The brightest cluster in the northern sky , Messier 13 , belongs to class V.
List of classes, each with an illustration: Shapley – Sawyer Concentration Class
The concentration classes are still used today by amateur astronomers, for example, to describe the optical impression to be expected when observing globular clusters. For scientific purposes, quantitative measures for describing the structure of the clusters are preferred, such as those obtained by adapting parametric models to the measured surface brightness profiles.
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- ↑ Harlow Shapley, Helen B. Sawyer: A Classification of Globular Clusters . In: Harvard College Observatory Bulletin . tape 849 , 1927, pp. 11-14 , bibcode : 1927BHarO.849 ... 11S .
- ↑ James Binney, Michael Merrifield: Galactic Astronomy . Princeton University Press, 1998, ISBN 0-691-02565-7 .