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The Science Behind: Leap Years

Posted at 4:41 PM, Feb 29, 2016
and last updated 2016-02-29 17:04:24-05

February 29th doesn't happen often.

In fact, it only happens every 4 years -- it's called a Leap Day.

We have Leap Years and the subsequent Leap Days because we use the Gregorian calendar.

According to the Gregorian calendar 1 year is 365 days. That's how long it takes Earth to orbit completely around the Sun.

However, in actuality, it takes 365.242 days to go around our biggest star (this is known as a solar year).

That's a small difference, but it adds up over time.

So, in order to stay on track, we have to make up for that near .25 difference every 4 years.

If we didn't have Leap Days then our days would be all mixed up...it would mid 2017 right now!

There is one exception to this "every 4 years" rule though.

All century years, i.e. 1500, 1600, 1700, 1800, 1900, 2000, etc. have to be divisible by 400 in order for it to be a Leap Year.

About 4.1 million people have been born on a Leap Day, and these people are often referred to as "Leaplings" or "Leapers."

The odds of being born on Leap Day are 1 in 1,461.

Now the question becomes, "what day do I celebrate my birthday?"

The answer is simple. If you're born before noon on February 29th, celebrate on February 28th. If you're born after noon on February 29th, celebrate on March 1st.

Our next Leap Year will be in 2020.

Be sure not to get Leap Years and Leap SECONDS confused.