Happy National Pi Day!

Here's to Being Irrational!

National Pi Day

Celebrate #NationalPiDay with 3.14 pieces of your favorite pie (à la mode, according to our recent poll), 3.14 slices of your favorite pizza (pie), 3.14 chapters of The Life of Pi, or by seeing how many decimal digits of Pi (π) you can memorize and say aloud. (FYI, there are over a trillion, so hydrate first.)

The Punny Side of Pi

• 3.14 backwards is PIE
• 3.14% of sailors worldwide are (Pi)rates.
• Pi may be irrational, but it's well-rounded.
• Too much π = a large circumference.

Pi Jokes

• Q: What do you get when you cut a jack-o-lantern by its circumference? A: Pumpkin Pi.
• Q: What do you get when you divide the circumference of the sun by its diameter? A: A p in the sky.
• Q: What is the official mascot of Pi Day? A: The Pi-thon.
• Q: Did you hear about the Pi'd Piper? A: He led the village children in circles.

Pi Reads

The Joy of Pi by David Blatner
Blatner takes an infinite number and makes it infinitely intriguing, humorous, and fun. From the quirky and trivial to the nerdy and weird, his tribute to Pi has the power to convert the most right-brained readers into 3.14 enthusiasts.

How to Bake π by Eugenia Cheng
Cheng takes math into the kitchen, combines it with cooking, gives it a life of its own, and makes it something you want to be friends with. Yes, she's a math professor, but it's her zest for cooking and “mathematics of mathematics" theory that reveals the magic of math.

A History of Pi by Petr Beckmann
Dr. Beckmann puts the development of Pi into a historical context that ties the history of math and the history of man together in mind-bending ways that make both subjects way more fascinating than they ever were in high school.

The Life of Pi by Yann Martel
For the not-so-mathematically-inclined who haven't read Martel's novel about Pi Patel and his 450-pound Bengal tiger frenemy Richard Parker, putting it in your cart and ordering it today is the perfect way to celebrate Pi Day. (And, we do the math for you!)

Contact by Carl Sagan
Math being the universal language and all, Sagan suggests in his follow-up to Cosmos that the creator of the universe buried a message within Pi's digits. Combined with the sum of his incredibly realistic predictions for the future of humanity, it's an interesting and thought-provoking theory.

Pi Fun Facts

Universcience's Palais de la Découverte (Discovery Palace) in Paris has a circular room with a dome-like ceiling known as the “Pi Room" with 707 digits of π inscribed on its walls. The numbers represent the 1853 calculation of English mathematician William Shanks, which actually has an error beginning at the 528th decimal place. (It was corrected in 1949.)

July 22 is "Pi Approximation Day" in countries that note dates in day/month/year format, because 22/7=3.142857.

Several of MIT's (Massachusetts Institute of Technology's) college cheers include "3.14159" in them, because nerd humor.

In 2011, one of Google's oddly specific bids for Nortel's (Northern Telecom) highly valuable portfolio of technology patents was π (billion), because even giant companies can be punny. (They lost to a consortium that included Apple, EMC, Ericsson, Microsoft, BlackBerry Limited, and Sony, who bid $4.5 billion.)

A History of Pi

The Greek letter wasn't used to represent the circumference of a circle to its diameter until the 1700s, but the earliest use of Pi as we know it was by the ancient Babylonians. They initially calculated the area of a circle by multiplying the square of its radius by 3, but by the time a tablet from ca 1900 – 1680 BC was etched, it had evolved to 3.125…closer to being accurate, but undershot by a bit. The ancient Egyptians, on the other hand, overshot slightly, using a value of 3.1605 in ca 1650 BC according to the Rhind Papyrus.

Archimedes of Syracuse lived from 287 to 212 BC and was one of the greatest mathematicians of the ancient world, was the first to actually calculate the ratio's value, at least that archeologists and historians know of. He used the Pythagorean Theorem to find the area of the polygon within a circle and the area of the polygon the circle was within. By finding the inner and outer limits of the circle's bounds, Archimedes was able to devise an algorithm that showed the circumference of a circle to its diameter to be between 3 1/7 and 3 10/71. In fact, another name for Pi is Archimedes' Constant.

Independently, a Chinese mathematician named Zu Chonghzi who lived from 429 to 501 and was unaware of Archimedes and his method, calculated the value of the ratio of the circumference of a circle to its diameter to be approximately 355/113 by using hundreds of square roots carried out to nine decimal places. In India, scholars devised the decimal system still in use today, and made other significant contributions to the world of math, including geometrically calculating Pi to five digits.

In 1706, William Jones became the first mathematician to use the Greek letter π, and Leonard Euler made it popular in 1737. Why π? Because it's the first letter of the Greek word perimetros, which means circumference.

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Read more by Beth Clark