A leap year, where an extra day is added to the end of February every four years, is due to the solar system’s disparity with the Gregorian calendar.

A complete orbit of the earth around the sun takes exactly 365.2422 days to complete, but the Gregorian calendar uses 365 days. So leap seconds – and leap years – are added as means of keeping our clocks (and calendars) in sync with the Earth and its seasons.

Why Are There Leap Years?

Leap years are needed to keep our modern day Gregorian calendar in alignment with the Earth’s revolutions around the sun.

It takes the Earth approximately 365.242189 days – or 365 days, 5 hours, 48 minutes, and 45 seconds – to circle once around the Sun. This is called a tropical year, and is measured from the March equinox.

However, the Gregorian calendar has only 365 days in a year, so if we didn’t add a leap day on February 29 nearly every four years, we would lose almost six hours off our calendar every year. After only 100 years, our calendar would be off by around 24 days!

Who Invented Leap Years?

Roman general Julius Caesar introduced the first leap years over 2000 years ago. But the Julian calendar had only one rule: any year evenly divisible by four would be a leap year.

This formula produced way too many leap years, but was not corrected until the introduction of the Gregorian calendar more than 1500 years later.

In 1582, Pope Gregory XIII revised the Julian calendar by creating the Gregorian calendar with the assistance of Christopher Clavius, a German mathematician and astronomer. The Gregorian calendar further stated that leap days should not be added in years ending in “00” unless that year is also divisible by 400. This additional correction was added to stabilize the calendar over a period of thousands of years and was necessary because solar years are actually slightly less than 365.25 days. In fact, a solar year occurs over a period of 365.2422 days.

Fun facts about leap years –

• The Summer Olympic Games are always held in a leap year. This year, they take place in Rio de Janeiro, Brazil.
• US presidential elections are held every four years, in a leap year.
• In Greece couples often avoid getting married in a leap year, believing it to be bad luck
• Food for thought: If you work on a fixed annual wage, today is just one more day’s work than you would usually have to do for your salary.
• As touched on above, a year that is divisible by 100, but not by 400, is not technically a leap year. Therefore 2000 was a leap year under the Gregorian calendar, as was 1600. But 1700, 1800 and 1900 were not. “There’s a good reason behind it,” Ian Stewart, emeritus professor of mathematics, told the BBC. “The year is 365 days and a quarter long – but not exactly. If it was exactly, then you could say it was every four years.” Pope Gregory and his astronomers’ solution will have to be rethought in around 10,000 years, Prof Stewart points out.

If you know any more Fun Facts about Leap Years, please share!

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