A Quick Leap Year History Lesson

Today is February 29, 2016 and is the first leap day since February 29, 2012. Leap days occur every leap year on the 29th of February and are fascinating for quite a number of historical reasons, but first let’s consider briefly how the concept of a leap year even arose in the first place, if only for the reason of a little added, attractive tidbit that will make you seem more interesting in your next conversation.

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Before the current Gregorian calendar which is adopted in almost every part of the world, was the Julian calendar and the Roman calendar. The Roman calendar was a pretty complicated fix that calculated days based on moon phases, it required a group of people to decide when days should be added or removed to keep the calendar in sync with astronomical seasons, marked by equinoxes and solstices.

As you can imagine, that was not an easy feat to accomplish every year and so the task of creating a more standardized calendar was taken up by Julius Caeser who consulted Alexandrian astronomer Sosigenes and together they created a calendar based entirely on the Earth’s revolution around the sun, also called a tropical year.


It was ascertained as most already know that the Earth on the average took approximately 365 days, 5 hours, 48 minutes and 45 seconds long (365.242189 days) to complete a full orbit round the sun. If however the calendar has only 365 days in a year, we would lose approximately six hours every year! In the Julian calendar therefore, a leap year occurred every four years with a leap day added to the month of February. At the time the leap day was actually February 24, February being as it was, the last month of the year. Due to an unfortunate calculation error, the leap years were not counted until 12 AD as the error made every third year a leap year.


The need for the Gregorian calendar arose when the Julian calendar became 24 days out of sync with fixed dates for astronomical events like equinoxes and solstices because the Julian calendar’s formula of calculating leap years every four years gave a leap year ever too often. The Gregorian calendar was therefore introduced in 1582 in nearly all countries and three criteria must now be taken into account to identify leap years;

  • The year is evenly divisible by 4
  • If the year is evenly divisible by 100, it is not a leap year
  • If the year is likewise evenly divisible by 400, it is a leap year

So there you have it, the history lesson that will help with awkward silences and uncomfortable conversations every leap year, you’re welcome.

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