Leap Year

Did you know that 2016 is a leap year? Well if you didn’t know that earlier, now you do! Many of you may be wondering a few things right now…. What exactly is a leap year? What is the purpose of a leap year? Are there any interesting leap year statistics? Read on to find out!

A leap year usually occurs every four years, except for certain century years. On a leap year, we add an extra day, called a leap day, to the shortest month of the year, February. This extra day, or leap day, occurs on February 29th. There are 365 days each year on regular non-leap years, but on leap years there are 366 due to the extra day that’s been added.

But why? Why do we add this extra day? It’s all about Earth’s revolutions around the sun. It takes the Earth 365.242216 days to revolve once around the sun, which is approximately 365.25 days. Some of you are probably thinking about how 365.242216 is not the same as 365.25, and we’ll get to that later. So, coming back to the 365.25 day approximation, in order to keep our calendar in alignment with the Earth’s revolutions around the sun, we have to add an extra day every four years to make up for the quarter of a day extra that the Earth takes (that we don’t account for on regular years) to complete a revolution around the sun. One fourth times four is equal to one, so that’s why we add an extra day to our calendar every four years. But was it always like this? No, but the concept has sort of been there for a while. Leap years were introduced by the Roman general Julius Caesar to the Roman Empire almost 2,000 years ago. The calendar the Romans followed was called the Julian calendar, and was named named after Julius Caesar, the person who created it. The Julian calendar only had one rule, and it was that any year divisible by four would be a leap year. However, by inserting one extra day every four years, that made a solar year equal 365.25 days, when a solar year was actually a little less that that- 365.242216 days. This made the Julian year about 11 minutes and 4 seconds too long. Although this doesn’t seem like much, over time the 11 minute 4 second surplus each year added up and was beginning to throw things off. In the 16th century, the spring equinox was falling around March 11th instead of March 21st. This was fixed in 1582 by Pope Gregory III, who created an exception to the rule of leap years that the Julian calendar had (every year divisible by four is a leap year). He created the Gregorian calendar, which we still use today, and the rule of leap years was that a leap year occurs every year divisible by four EXCEPT century years, which have to be divisible by 400 to be a leap year. So, for example, the year 2100 will NOT be a leap year.  This was done to fix the surplus error that the Julian calendar had.

What about birthdays? Do people who have a birthday on a leap day only age and celebrate their birthday every four years!? To start, there are about 187,000 people in the US and 4 million people in the world born on a leap day. Your chances of being born on a leap day are about 1 in 1,500. People born on a leap day do age like everyone else :). Most celebrate their birthday on March 1st. For things like when you can get your driver’s license, states have their own rules, but most of them consider March 1st the official day for those born on a leap day.

I hope you enjoyed your leap day this year on Monday, February 29th! Remember, leap years only occur every four years (usually), so make the best of an extra day!


–Shruthi Sathish

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