The Trumpler classification system is a method used by astronomers to categorize star clusters based on their brightness and the presence of individual stars. Developed by astronomer Robert Trumpler in the early 20th century, this system helps in understanding the structure and composition of star clusters. It classifies clusters into three main types: open clusters, globular clusters, and associations. In this system, clusters are further classified by their apparent brightness and the number of stars they contain. The classification includes a letter designation for the cluster type and a numerical scale that indicates the cluster's richness and concentration. This helps astronomers study the evolution and dynamics of star clusters in the universe.