Today, we're told (though we've done no independent research to verify either of these claims) is both Einstein's birthday, and Pi Day. The first of those needs no explanation, I imagine: you all know who Einstein was (think shaggy hair and relativity if you're drawing a blank). Pi Day, on the other hand, might not ring any bells, but I assure you it's quite simple. Pi is some sort of Greek letter, and math types use it to represent a number: in fact, the number you get when you divide some part of a circle by some other part. Something along those lines.
In any case, the number pi (and if I could get some unicode action up in the house here I'd show you something like π) is an irrational number, which means it can't be represented in decimal form: only approximated. And they approximate it as 3.141592... &c &c; so you see why it's celebrated today, which is 3/14 in the American style. (Observant readers will note that neither Pi Day nor its close relative Mole Day can be celebrated in England or, indeed, anywhere else in Europe (I don't think). Just another thing we've got on those dirty Yooropeans.)
Now, as to the question of why pi is so celebrated, we come to a trickier matter. After all, I understand that there are other irrational numbers out there--hordes of them, even--as well as things called 'imaginary numbers,' which sound even more fun! (for numbers, that is: you gotta cut em some slack). And yet pi seems to be folk's favorite. In that movie Contact (warning: hideously irritating Flash intro) it was even said to contain a secret message from the aliens, or at least from some aliens anyways. Maybe that's it. Or maybe math teachers just need something to get excited about.
In any case, I'm aware that I've imparted you this information too late for you to be able to do much with it in the way of celebrating or trying to get off work/school (unless you're in Hawaii or the Aluetian Islands or something), but in case you're curious for next year, I've aquired some tips about how Pi Day is meant to be observed. Ready? Eat pie, and act irrationally. Ha ha, get it? Although I must say I'm quite in favor of both of those suggestions on general principles, so I can't really object. It might be kind of like Lent to a vegetarian though: how will we be able to tell my Pi Day from any other day of the year?!
Oh yeah, and besides Einstein Day and Pi Day today is also Theresa's birthday, so a big shout-out to her: Happy Birthday! She's a math and physics type, so I guess she picked a good date to be born.