Happy Pi Day, everyone! March 14 (3.14) at 1:59 (you get the idea) is the peak of Pi Day, a celebration of the Greek letter which represents the irrational number by which the diameter of a circle is multiple in order to obtain the circumference ... but you guys knew that, right?

The sixteenth letter of the Greek alphabet, p, was first used for the familiar value 3.1415"¦ in the publication, "Synopsis Palmariorium Mathesios," authored by William Jones in 1706, though the fact that "the ratio of the circumference to the diameter of a circle is the same for all circles, and that it is slightly more than 3, was known to ancient Egyptian, Babylonian, Indian and Greek geometers." 2006 was the 300th Anniversary of the introduction of the mathematical symbol pi. (Here's more on the history of Pi.)

Be prepared for 3.14.2009 by ordering a mental_floss "Simple as 3.141592..." shirt (men's or women's). Keep reading for more pi facts.

When I was in high school, my math teacher, Ms. Coffield, encouraged us to celebrate Pi Day for extra credit, but it always turned out to be much more. Some students made necklaces, I wrote a poem, and others competed to see who could memorize the most digits. In this video, savant Daniel Tammet discusses with David Letterman how he recited 22,514 digits of pi from memory on Pi Day 2004.

From our Amazing Fact Generator: "In 1897, Indiana tried to pass a bill stating that pi is equal to 3.2 as opposed to its truly infinite value, but it never became law due to an intervention by a Purdue University professor."

Unfortunately, even in 2008, some people are confused about pi. Check out this picture below taken by a student at Georgia Southern (sent to me via my high school math teacher), where someone thought Pi Day was March 13, and that the digits were 3.13 ...

When I was asking for Weekend Links awhile back, Brian from San Francisco sent in this gem regarding pi that I saved until now:

"A work I am continually impressed by is "Poe, E.: Near a Raven," a constrained writing experiment that encodes 740 digits of Pi in a poem evoking Poe's 'The Raven.'" It's pretty cool, and helps illustrate that the concept of pi is all around us!

So today, try and have more fun with pi! Find out if your birthday is in the first 1254543 digits. And if you think you know all there is to know about 3.14, try your hand at this quiz. For those who are huge fans of pi, you can now smell irrational, too.

How many digits of pi do you know? This song may help. Does anyone else celebrate Pi Day? What are some of your activities or memories from it?