Have you ever stopped to wonder why it is that every four years, February has an extra day? A leap year, or intercalary year, is where the calendar contains one extra day to keep them in line with the seasons. Over time, rigid calendars cause each year to drift and fall out of alignment with the seasons. To counter this, inserting (or intercalating) an extra day into the year stops the drift from happening. This is how we get leap years.


1. Who invented leap years?

Nearly 5000 years ago, the Sumerians split the year into 12 equal portions of 30 days each and created a 360 day year. However, this meant that their year was almost a week shorter than the time it takes for a complete journey around the sun. Soon their calendars fell entirely out of alignment.

Recognizing the drift in this, the Ancient Egyptians were the originators of a calendar that spanned 365 days. Rather than a leap year, they simply added five days of festivals and celebrations at the end of the year.

the first leap year cinoby / Getty Images


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