Today is Feb. 29, 2016, a day better known as Leap Day.


The last time our calendars read Feb. 29 was back in 2012. The Gregorian calendar we follow in the U.S. consists of 365 days and it’s common knowledge that one rotation of Earth takes approximately 24 hours. Our seasons change from spring, to summer, to fall, and then to winter as the Earth makes its revolution around the sun. One full revolution equals 365 days, right?


Almost.


It actually takes the Earth a little longer than 365 days to make a full revolution around the sun — 365 days, 5 hours, 48 minutes, and 45 seconds to be exact. That’s approximately 365.25 days. In order to keep our calendar on track, those four quarter-days are added up into one full day every four years. This extra day is added to the shortest month of the year — creating Leap Day, Feb. 29.


2016 Leap Year 2016 Leap Year


While the United States and most other western countries follow the Gregorian calendar, many other countries follow their own. As a result, they make up for the extra quarter of a day in different ways. The Chinese and Hindu calendars add a “Leap Month” once every three years. In Iran, an extra day is added to the last month of a Leap Year. A Jewish Leap Year consists of 13 months, each with 29 or 30 days.


The next Leap Year in the United States occurs on Saturday, Feb. 29, 2020.