A star cluster is a group of stars that are physically close to each other in space, bound together by gravity. There are two main types of star clusters: open clusters and globular clusters. Open clusters, like the Pleiades, contain young stars and are often found in the Milky Way galaxy. Globular clusters, such as M13, are older, densely packed groups of stars that orbit the galaxy's core. Star clusters are important for astronomers because they provide insights into stellar evolution and the formation of galaxies. By studying the stars within a cluster, scientists can learn about their ages, compositions, and the processes that govern their development over time.