Shapley–Sawyer Concentration Class

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
I High concentration toward the center
II Dense central concentration
III Strong inner core of stars
IV Intermediate rich concentrations
V Intermediate concentrations
VI Intermediate mild concentration
VII Intermediate loose concentration
VIII Rather loosely concentrated towards the center
IX Loose towards the center
X Loose
XI Very loose towards the center
XII Almost no concentration towards the center



  1. ^ Hogg, Helen Battles Sawyer (October 1965). "Harlow Shapley and Globular Clusters". Publications of the Astronomical Society of the Pacific. 77 (458): 336–46. Bibcode:1965PASP...77..336S. doi:10.1086/128229. JSTOR 40674226.
  2. ^ Burton, Jeff (July 26, 2011). "Shapley–Sawyer Globular Cluster Concentration Class". Archived from the original on March 22, 2012.