... part of a much larger cluster of clusters – the Local Supercluster. The existence of galactic clusters presented a riddle to scientists for many years – the “missing mass” problem. Clusters ... largest galaxy in the group; the Milky Way, the second-largest galaxy; and the Trianglum Spiral, the third largest. There are also four medium-sized spiral galaxies, includ- 10 ing the Large Cloud ... formations should not be confused with stellar clusters, globular clusters of stars that exist within a galaxy. The size of galactic clusters varies enormously, with some clusters containing only...