Here's the question: The following ﬁgure is the H-R diagram of a star cluster. Use this diagram to determine the age of the cluster. The answers are multiple choice: (A) 600 thousand years (B) 6 million years (C) 60 million years (D) 600 million years (E) 6 billion years Here's my attempt: I know that to determine the age of the cluster, we need to start by determining where in the graph the stars start changing from main sequence. And at that point, we find on the horizontal axis one of the following: OBAFGKM And then the letter has 10 sub-groups, so I believe the classification to be G2 or G1. This is the part I'm stuck on, if it is G1 or G2 (or pretty much any sub-group of G in general), how do I get the age? I read in my textbook that G1 is about the age of the Sun, but all of the multiple choice answers are 6-something and I don't understand how to get that, or at least something close to that. I determined the answer to be 10^10, which is 10 billion, I believe. But it's really off and completely wrong. Thanks in advance.