Whew. Finally back after two snow days and then a 3 day weekend and a 2 hour delay today! We are on to the HR diagram today and a quick discussion of relative abundance of stars. The above diagram is one of my favorites. Always interesting to talk about how big a million cubic parsecs would be. The question of the week on xkcd is about stars and grains of sand but with a twist worth thinking about! Click on image below.