Yesterday I had a "bad Christian" moment.
As we were looking at the holiday calendar for 2016 a coworker asked why Easter moved each year. I knew it had something to do with the holidays surrounding it but I couldn't give her a straight answer.
So like any American I went straight to Google (actually first I asked someone else THEN I went to Google). The reason Easter moves is because it must follow Passover. Since Passover is a Jewish holiday it follows lunar/solar calendars and so the days shift.
Boom. Now I have an answer next time someone asks.