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In General

• Why are most stars we see in binary systems, grups or clusters?

Open Clusters

• What are the Pleiades?
• What is an open cluster?
• How many stars do open clusters usually have?

Globular Clusters

• What is Omega Centauri?
• What is a globular cluster?
• How many stars do globular clusters usually have?
• Are there globular clusters in our galaxy?
• How do the sizes (number of stars) of open and globular clusters compare?

Ages of Clusters

• Why would we want to plot all stars of one particular cluster in an HR diagram?
• How can you find out the age of a star cluster?
• In a star cluster, why do massive stars leave the main sequence before low-mass stars?
• How old are the globular clusters, in our galaxy?
• Which star clusters are usually older, in our galaxy?
• How do the ages of open and globular clusters compare?