Happy Leap Day! Was anyone born on Feb. 29? I didn’t miss it by much. I suppose you all know that a leap year is any calendar year divisible by four. Or you think you know. Years that also are divisible by 100 are not leap years—unless they also are divisible by 400, then they are leap years. Got it? All this is, of course, necessary because the earth does not revolve around the sun in exactly 365 days. It takes about five hours more. When the Gregorian Calendar was developed back in the 16th century, this was taken into account, so people would not have to wonder if they should wear a coat to the Christmas party.