Pi Day Celebrates a Mysterious Number

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Math lovers honor Pi Day by eating pie, of course. NPR hide caption

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A lot of people are excited about the power of pi. But not everyone knows it has an official celebration — Pi Day, on the fourteenth day of the third month, 3.14. Those are the first three digits of pi, that transcendental number, the icon with the digits after the decimal point that go on forever.

Strictly speaking, pi represents the constant ratio of a circle's diameter to its circumference. There is no pattern to pi. But it's a cool number with real-life applications. Today, as Dan Hellerich of PiDay.org reports, numbers geeks all over the world bake pies, write "pi-kus" and recite pi to as many decimal points as possible. "I know 15," he says. "Some people know 10 times that, but you really only need about 10 to do accurate math in geometry or physics."

Pi has been around a long time. A man named William Jones identified the magical number in the 1700s. But the dedication of day to the love of pi is a more recent development. And — as another pi super-fan says — unless our calendars get a major adjustment, no other date can hope for 3.14's level of distinction.

"You can't find a 'square root of two' day," the super-fan says. The square root of two is roughly 1.44. "That would be January 44. And E? That would be February 71. You can't celebrate that."

On our blog, a challenge: Write your own "pi-ku".

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