Star clusters are elegant and pretty things to see in a telescope, but that's not the whole story. We know that stars must change as they run out of hydrogen to burn in their cores, and those deep changes in the core of stars have observable consequences. So, we use HR Diagrams to map the changes and enormous computer simulations to test the physics. This is part of my complete intro Astronomy class that I taught at Willam Paterson University and CUNY Hunter. Hertzsprung-Russell diagram Hyades Star Cluster Open Clusters Globular Clusters NOAO image gallery The STScI Digitized Sky Survey M67 on APOD M80 Hubble Space Telescope My lab on the Hubble Legacy Archive Educational Materials Stellar Evolution Main Sequence Lifetime Main Sequence Turn-off The Hertzsprung-Russell Diagrams of Star Clusters 0:00 Introduction 0:44 The Hyades Star Cluster 3:55 The Two Types of Clusters 4:59 Open Clusters 5:40 Messier 11 in context... 6:46 The Wild Duck Cluster: Messier 11 7:57 The Pleiades; M45: The Seven Sisters 8:25 The Perseus Double Cluster 9:05 Messier 67 11:19 Messier 41 14:35 Globular Cluster Messier 55 15:24 NGC 2808 16:08 Messier 92 16:34 Globular Cluster Messier 13 17:39 Messier 80 19:13 NGC 5139: Omega Centauri 20:38 Stars in space versus stars in the HR diagram 21:09 M55 Color-Magnitude Diagram 22:27 The Main Sequence, Revisited 23:21 Stars Live their Lives out... 24:20 Progressive Evolution 25:14 HR Diagram of the Pleiades 26:04 M67 HR Diagram 27:38 HR diagram for the globular cluster 47 Tucanae NGC 104 is about 28:21 H-R Diagrams of a Model Star Cluster 31:25 HR Diagram for Globular Clusters 31:35 Main Sequence Turn-off 32:24 Conclusions 33:31 Observing Stellar Evolution in Star Clusters 33:51 REVIEW QUESTIONS.