The Shapley–Sawyer Concentration Class is a classification system on a scale of one to twelve using

Roman numerals Roman numerals are a numeral system that originated in ancient Rome and remained the usual way of writing numbers throughout Europe well into the Late Middle Ages. Numbers are written with combinations of letters from the Latin alphabet, eac ...

for

globular cluster A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...

s 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 Palomar 12 is a globular cluster in the constellation Capricornus, and is a member of the Palomar Globular Clusters group. First discovered on the National Geographic Society – Palomar Observatory Sky Survey plates by Robert George Harri ...

. (The class is sometimes given with numbers lass 1–12rather than with Roman numerals.)

History

From 1927–1929,

Harlow Shapley Harlow Shapley (November 2, 1885 – October 20, 1972) was an American scientist, head of the Harvard College Observatory (1921–1952), and political activist during the latter New Deal and Fair Deal. Shapley used Cepheid variable stars to estim ...

and

Helen Sawyer Hogg Helen Battles Sawyer Hogg (August 1, 1905 – January 28, 1993) was an American-Canadian astronomer who pioneered research into globular clusters and variable stars. She was the first female president of several astronomical organizations and a ...

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''.

Classes

References

Astronomical classification systems * {{star-cluster-stub