It's around this time every year that math nerds unite to celebrate National Pi Day, a day honoring the mathematical constant pi, or 3.14. March 14 (or 3/14) is officially Pi Day because the date represents the first three digits of the number used to represent the ratio of the circumference of a circle to its diameter. But this year, Pi Day is taking it up a notch. On 3.14 at 9:26:53 a.m., the date and time will correspond to the first 10 digits of pi: 3.141592653

That's something that happens only once per century.

Pi Day was first celebrated officially in 1988 at San Francisco's Exploratorium, an interactive science museum. It has been celebrated there every year since. In 2009, the U.S. House of Representatives declared March 14 to be National Pi Day, passing a resolution to celebrate the importance of math and science in daily life.

What's so special about pi? It's kind of hard to wrap your head around the complexity and simplicity of a number, but the thing about pi is that it's both infinite and universal. It has been calculated to more than 1 trillion digits beyond its decimal point. And yet it still keeps on going. Pi represents the ratio of a circle to its diameter. Every circle. Every time. Measure the circumference of your tea cup and then measure its diameter. The difference? Pi. The same goes for the tires on your car or your salad plate or your kids' trampoline.

Want to test it out? Take a toilet paper tube and measure the distance across. Then cut it down the edge and roll it out so that it's flat. Measure that. It will be pi (or 3.14) times the first measurement you took (which was the diameter.) Mind. Blown.

National Pi Day is celebrated as a day to spark an interest in math among those who might not normally see mathematical concepts as fun. Around the world, people celebrate the day by eating pies, throwing pies, and even reciting pi from memory in competitions. Some musicians have even interpreted the digits of pi into a musical composition.

Check out this site for more fun ways to celebrate National Pi Day.

And one more cool thing about Pi Day: It also happens to be the birthday of Albert Einstein. Coincidence? I think not.

Math fans celebrate once-in-a-century Pi Day
This year, for the first time in 100 years, National Pi Day will go beyond 3.14 to celebrate the first 10 digits of pi.