Something useful I actually learned in math class

In math we have recently began studying circular trig. This would be of no particular interest to me except that my teacher has decided that we should include a little bit of math history in the unit. Well, in the process of talking about how the Babylonians decided there should be 360 degrees in a circle we got slightly off topic and somehow got onto the topic of leap years. Now I thought I understood leap years: they are used to compensate for the fact that each year is a little more than 365 days. I was mistaken, though, in thinking we just added a day every four years. There is actually a complicated system of making sure that our calendar stays on track. I found this whole thing about math history and calendars quite fascinating, even the part on radians (if you don't know, don't ask.) If you like me, are enough of a geek to learn more you can click here.