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Happy Pi Day! Here's some fun facts about 3.14159265359...

a pie with the pi sign on it
Andrew Martin

Monday is March 14 — aka 3/14 — a k a Pi Day, a day to celebrate math, often with a slice of yummy dessert.

You likely remember pi from middle school or junior high. It's the ratio of a circle's circumference to its diameter, which has been determined over hundreds of years to always be about 3.14.

"There are a lot of places that pi comes up naturally," says Karen Smith, Ph.d., associate professor of Mathematics at UC Blue Ash.

"For example, NASA uses pi regularly to calculate trajectories of space craft. It was used by early astronomers to study the Earth and its rotation and orbit. It's also used nowadays when any kind of building construction is going on — anything that is circular or has circular parts, like arches or circular pillars — where those kinds of calculations have to be done."

Fun facts about pi

The first Pi Day was celebrated in 1988 in California.

"It was organized by a physicist named Larry Shaw out in San Francisco," Smith reports. "They celebrated by eating pie, of course, and marching in circles."

Pi Day was officially designated by the U.S. House of Representatives in 2009.

Math teacher William Jones "invented" pi in 1706 when he was the first to use the Greek letter π (pi) as the symbol for the mathematical ratio.

"Before that time, it was known as 'the quantity which when the diameter is multiplied by it, yields the circumference.' Quite a mouthful," Smith quips.

While Jones gave the concept a name, its roots are much older.

"There were many ancient civilizations that used approximations of pi in calculations, but it was Archimedes who was the first to do a calculation of pi," Smith explains. "He found the areas of two regular polygons, one inscribed inside a circle and one outside, and he was able to then show that pi is between 3-1/7 and 3-10/71. So a pretty precise calculation."

Renowned physicist Albert Einstein was born on Pi Day. His birthday is March 14, 1879.

Bonus pie fact:

The word for the tasty dessert — pie — comes from "magpie," like the bird. That originally came from the Latin, "pica." The story gets pretty long from there. The magazine Bon Appétit explains.

This story was edited to add a missing digit in the headline.

Senior Editor and reporter at WVXU with more than 20 years experience in public radio; formerly news and public affairs producer with WMUB. Would really like to meet your dog.