Collinder Catalog
The Collinder catalogue (1931) is a historical, uniform survey of open clusters, ranging from bright showpieces to very faint or uncertain groupings. Per Collinder included every object that showed a measurable stellar concentration on the photographic plates of his time, creating a consistent dataset for comparing cluster size, structure and density. It is therefore not a selection of the “best” clusters, but a systematic snapshot of all recognisable open clusters available with the observational technology of 1931.
