Alter, G., & Ruprecht, J. (1963). The system of Open Star Clusters and our Galaxy: Atlas of Open Star Clusters. Academic Press.

Alter, G., and J. Ruprecht. The System of Open Star Clusters and Our Galaxy: Atlas of Open Star Clusters. New York ; Praha ; London: Academic Press, 1963.

Alter, G., and J. Ruprecht. The System of Open Star Clusters and Our Galaxy: Atlas of Open Star Clusters. Academic Press, 1963.