It’s Leap Day today, and that means people born on February 29th finally get to have a birthday. But why do we have Leap Years? What’s the purpose? Well, it ensures that our seasons don’t drift.

You see, it takes the Earth 365.256363004 days to orbit the sun (this is known as the sidereal year). The calendar year is 365 days. But every 4 years, we have an extra day. So, we add a day to the years that can be divided by 4. This year is 2016, and is divisible by 4.

Sounds simple, doesn’t it? But it gets a bit complicated.  This accounts for 365.25 days. But what about the extra 0.006363004 days? This accumulates, and after 400 years, it equals about 3 days extra. So, we have 3 too many Leap Days every 400 years. So what do we do? We just drop the Leap Days that…