# Happy Pi Day!

How are you celebrating this once in a century event?

Chances are that unless you teach math, the last time you thought about the number pi was about the same time you stopped crushing on the hot guy in AP English.

But it’s time to renew acquaintance with this elegant number because this Saturday is not only the annual Pi Day (3.14 – get it?) but the best Pi Day of this century, 3.14.15, the date corresponding to the first five digits of pi.

And it’s about to get raucous, or as raucous as a date commemorating a mathematical constant gets. Both the University of Houston and Texas A&M University will have parties. The Children’s Museum of Houston will celebrate its sixth annual Shaving Cream Pi(e) Fight at 1:59 p.m. Saturday, 9 being the next digit in pi.

What’s all the fuss? Isn’t pi about, like, circles or something?

Sit back, grasshopper, and listen to the professors.

Pi, often depicted as the Greek letter π, is the ratio of a circle’s circumference to its diameter. It was discovered independently by many cultures over the centuries, probably starting with the Babylonians about 4,000 years ago, says Bernhard Bodmann, professor of mathematics at the University of Houston. The Babylonians, though, weren’t terribly accurate and put its value at about 3.

The real early hero of pi is the Greek Archimedes in the third century B.C., says Frank Sottile, math professor at Texas A&M. The Greeks knew, as you learned in school, that the circumference of a circle is 2 πr, and that the area of a circle is πr², but they didn’t get that the two pis were the same thing. “Archimedes showed that π=π,” he says.

Another cool thing? The volume of a sphere such as the Earth is 4/3 πr³.

Pi’s true beauty is its simplicity, says Scott Chapman, a math professor at Sam Houston State University and editor of the American Mathematical Monthly.

“It’s the best example of a nonsimple number that a person on the street can understand,” he says. School kids know it. Contrast that to e, or Euler’s number, another constant of note. “To understand e, you’d have to remember what a natural logarithm is,” Chapman says. That’s calculus. Ahem.

True enough, but as the great Leonhard Euler taught us, e^(πI) + 1 = 0. It’s all connected somehow. If you’d like to know more about this magical number, I recommend the book A History of Pi. Originally published in 1970 by Petr Beckmann, it’s a little dated, especially when Beckmann goes off on the occasional historical/political rant (executive summary: he did not like the Germans or the Roman Empire), but it’s a great overview how we learned what we know about pi. It doesn’t skimp on the math, so be prepared to exercise those parts of your brain, but it’s well worth the effort. Happy Pi Day!

UPDATE: Some awesome visual representations of pi.