Hey, high school junior in an AP-level Astrophysics class reporting in... I have a short question about the equation in the subject line. This equation was in my textbook, but with almost no explanation whatsoever. Yes, it explained how to apply the equation, but not where it comes from, why it works, how it is derived, etc. So, my teacher wants us for homework to find out those things. I've googled and looked everywhere I have to look, but I can't find a proper explanation. I'm worried I'm going about this the wrong way... Any help would be appreciated, thank you.