Why are star clusters important in studying stellar evolution?
Star clusters are groups of stars fixed by gravitational fields that hold them togheder. As they were all born from a common gas cloud, they all have roughly the same age and composition. Stars properties depend only on mass, being a wonderfull natural laboratory for stellar evolution studies. When a cluster, near enough, is settled in the Hertzprung-Russell diagram, as the luminosity is well known, and the distance can be measured by the parallax method, comparing with far clusters will give us the distance to them. Have in mind that a cluster can be observed a lot more far than a single star, and that using all stars in the cluster will give better results in the H-R than using a single one, being a very good method for accurate distances calculations. Of course, interactions between close stars can be also observed, as well as formation models.
