Shapley–Sawyer Concentration Class

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The Shapley–Sawyer Concentration Class is a classification system on a scale of one to twelve using Roman numerals for globular clusters according to their concentration. The most highly concentrated clusters such as M75 are classified as Class I, with successively diminishing concentrations ranging to Class XII, such as Palomar 12. (The class is sometimes given with numbers [Class 1–12] rather than with Roman numerals.)


From 1927–1929, Harlow Shapley and Helen Sawyer Hogg began categorizing clusters according to the degree of concentration the system has toward the core using this scale. This became known as the Shapley–Sawyer Concentration Class.[1]


Class Description Example
01 I

High concentration toward the center
02 II

Dense central concentration
03 III

Strong inner core of stars
04 IV

Intermediate rich concentrations
05 V

Intermediate concentrations
06 VI

Intermediate mild concentration
07 VII

Intermediate loose concentration

Rather loosely concentrated towards the center
09 IX

Loose towards the center
10 X

11 XI

Very loose towards the center
12 XII

Almost no concentration towards the center
Palomar 12



  1. Hogg, Helen Battles Sawyer (October 1965). "Harlow Shapley and Globular Clusters". Publications of the Astronomical Society of the Pacific 77 (458): 336–46. doi:10.1086/128229. Bibcode1965PASP...77..336S. 
  2. Burton, Jeff (July 26, 2011). "Shapley–Sawyer Globular Cluster Concentration Class". Archived from the original on March 22, 2012.