Most people know that when we have Leap Year, almost every four years, our year will consist of 366 days, versus the common 365. During Leap Years, we add a Leap Day, known as an intercalary or extra day, that is established on February 29th in our modern day Gregorian calendar. What many people don`t know is why.

There are scientific reasons behind why we have Leap Years, they are needed in order to keep our calendar in alignment with the Earth`s orbit around the sun. The Earth takes roughly 365.242199--or 365 days, 5 hours, 48 minutes and 46 seconds to orbit fully around the Sun. However, the modern Gregorian calendar that we use only accommodates 365 day in a year. If we did not add that extra day for Leap Year, we would lose approximately 6 hours off our calendar every year, which after a century would add up to our calendar being off by about 24 days!

Leap Years in the Gregorian calendar even have their own criteria that must be met. The year must be divisible by 4, if the year can be evenly divided by 100 it is not a Leap Year--unless the year is also evenly divisible by 400, then it is a leap year. In other words, 2000 and 2400 are both Leap Years but 1800, 1900, 2200 are not Leap Years.