# Here’s the science behind why Saturday is Leap Day

## An extra day is added to February almost every four years

SAN ANTONIO – Those who have a birthday on February 29th know all too well what Leap Day is all about. But, for the rest of us, you might not realize that Earth’s revolution around the sun takes 365.242189 days or 365 days, 5 hours, 48 minutes, and 45 seconds. In other words, our calendar year is not exactly 365 days.

To make up for that small difference, a day is added to our calendar almost every four years. If it wasn’t, over time, our seasons would eventually get out of sync. Give it a few centuries and we, in the Northern Hemisphere, would be celebrating Christmas in the summer!

But, let’s get back to the whole almost every four years thing. If we added a Leap Day every four years, the math still wouldn’t work out exactly right so there are some exceptions.

The year must be divisible by four. If it can be divisible by 100, it is NOT a leap year UNLESS it is divisible by 400. The year 2000 was one of those weird exceptions. While it was divisible by 100, it was also divisible by 400, making it a leap year. Follow?

If all of this makes you head hurt, you can blame Julius Caesar. He introduced the idea of adding a leap day more than 2000 years ago and the amended calendar was named in his honor: the Julian calendar.

We now use the Gregorian calendar, named for Pope Gregory VIII, which made the corrections to leap year that we use today.