A slice of pi for March 14, 2015

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.

Pi is irrational, the professors say, which says nothing about its state of mind. "Irrational" means it can't be shown as a fraction using whole numbers. Though 22/7 is sometimes used, says Chapman, "that's just something pop culture tries to pass off."

Pi is also transcendental, which means it's geometric but it's not the solution to any algebraic equation. Contrast it to the square root of 2, which is irrational but actually can be the solution to an algebraic equation, Bodmann says.

And, as almost everybody knows, pi goes on forever. A&M is starting its Saturday festivities, which Sottile has organized with grad student Kaitlyn Phillipson, at 9:26:53, the "pi second," taking pi out to 3.141592653, he says.

Pi has, however, been calculated (using computers) to the millionth nonrepeating digit - "an infinite nonrepeating decimal," Chapman says - and contests testing who can recite the most digits are a common feature of Pi Day festivities. Bodmann says there's a common memory trick for the moderately hardcore that uses a variation on Edgar Allan Poe's poem "The Raven" that matches the number of letters in each word to the digits in pi. He's tried it, and it seems to work.

A&M students will be inscribing thousands of pi digits outside the math building Saturday.

The professors say pi is stunning in its ability to show up in not just geometry but number theory, physics, harmonics, making digital music, chemistry, particle studies, even nature. Sottile cites a test called "Buffon's needle," which says that if you lay out sticks parallel and equidistant to each other, the probability that a stick dropped on them will cross another can be expressed with pi.

Chapman is surprised that Pi Day festivities have taken off in the past 10 or 15 years. "I like having an excuse to get more people into math than are already," he says. "It's the one day it's better to be at work. Celebrating pi is an excuse to celebrate math in general."

So if pi is this wonderful, mysterious, incredibly useful concept, why don't we all find this out in school?

"Come to my school, and you'll learn that," Sottile says.