The purpose behind Leap Day is actually very much driven by math, science, and necessity. For example, Feb. 29 occurs every four years if that year is evenly divisible by 100 or if it is evenly divisible by 400. This is because earth does not rotate around the earth every 365 days. Earth actually takes 365 days, 5 hours, 49 minutes and a few odd seconds, so every calendar year has to compensate for a quarter of a day. Happy Leap Day!