It's Pi Day which may, or may not, stir up a nightmarish flashback to those endless math lessons of your youth because it's all about that irrational number 3.14159265358979323846264338327950288419716939 (and on and on). Pi is, lest you forget, the simple ratio of a circle's circumference to its diameter—it's an infinite string of numbers, and very definitely isn't "3.2," no matter what Indiana thinks.

Why today? Because it's March 14th, of course. Or, 3.14, if you will. In two years Pi day will be even more fun (think about it).

Unlike other, more widely recognized holidays (watch your back, Valentine's!), Pi Day is a celebration of an altogether different, more boffin-friendly type. It's a celebration we can all get behind because all of us, even if you don't know it, have a life that's in many ways defined by pi because it's critical for the math that makes everything from your TV to your microwave work.

Pi Day is, in fact, something brands, scientists, cake-bakers, and practically everyone else can celebrate. Even the White House Twitter feed has joined in the fun, earning itself a few geeky PR points as it does so, by wishing us all a "Happy Pi Day" and tweeting a picture of the President with a kid shoveling pie (...yes, we know) down his youthful gullet. General Electric has used a fun trick in Twitter to make its Happy Pi Day wish dominate everyone's tweet feeds. A minute before 2 a.m. this morning (i.e. 3/14 1:59) Caltech students threw a pie party which ended up as a story in the *Los Angeles Times*. A special celebration in France is being hosted by the man who, aged 25, recited 22,514 digits of pi from memory in 2004—a European record. And if you think you can't remember even four or five places, a nice PBS post is here to help with a mention of a book written in pi language, where each word's length represents a digit of pi.

Welcome to Pi Day. Have a splendidly mathematical time.