Final answer:
Star clusters are useful for studying stellar evolution because all the stars in a cluster have nearly the same age. This allows astronomers to observe how stars of different masses go through each stage of their lives. Observing a cluster helps validate models of stellar evolution.
Step-by-step explanation:
Star clusters are useful for studying the early stages of stellar evolution because all the stars in a cluster have nearly the same age. When stars in a cluster have the same age, they differ mainly in mass, which determines how quickly they go through each stage of their lives. Observing a cluster allows astronomers to see many stages of stellar evolution among the members of a single cluster, helping to validate our models of stellar evolution.