If you're a mathematician, physicist, or engineer, you've probably already heard of Pi Day.

If you haven't, you would be surprised by how many people have. Pi Day--a celebration of the number pi, or roughly 3.14159--seems like something only for geeks, but it's also a great example of how an unlikely idea can wheedle its way into the status quo.

Think about it: The founders of Pi Day have taken something only a few people ever think about, and even fewer care about, and turned it into a phenomenon that's celebrated by thousands. Pi Day has also garnered its own resolution in the U.S. House of Representatives (and let's face it, those people can't agree on anything) and has been featured in news outlets from *USA Today* to *NPR*.

Granted, Pi Day was started sort of by accident. Larry Shaw, a scientist at the San Francisco Exploratorium, just put out pie for some of the staff on March 14, 1988. The next year, some museum visitors noticed and asked what was going on. Pi Day got bigger--and weirder--from there.

If you're starting with just the germ of an idea and need to convince huge swaths of people to adopt it, there's a lot you can learn from Pi Day.

**Start with something real. (But it can be absolutely anything.)**

Pi Day celebrates a number. Given that the big holidays are either religious or historical in nature, this is a pretty serious handicap. Pi is special: It occurs repeatedly throughout geometry, but also, says Ron Hipschman, a scientist at the Exploratorium, "anytime you have cycles, frequencies, or anything that’s rotating. It’s in tons of different places." Pi has been calculated to 10 trillion digits, and counting. But still. In the end, it's 3.14, or thereabouts.

**Capitalize on serendipity.**

Pi Day has a few things going for it. For one, it happens to be Albert Einstein's birthday. That's a nice coincidence, although it hasn't really paid off, other than giving a boost to Pi Day celebrations in Princeton, New Jersey, Einstein's longtime home.

More important: Pi sounds like pie. That's awesome. Plus, pie is circular, and pi is all about circles. Americans may not like math much, but pie? Absolutely.

The Exploratorium serves free pie on Pi Day--1,500 slices last year--but they're not the only ones. The American Pie Council has gotten into the act, publishing a Pi Day pamphlet with both math problems and recipes. Some bakeries and pizza shops are offering pies for $3.14, or pies that can be eaten in three-and-a-bit bites.

**Make it family-friendly.**

Obviously, there are rules, both legal and ethical, that restrict marketing to children. That's how it should be. But if there's something about your idea that can appeal to the entire family, not just to adults, go for it. If your idea has any redeeming value whatsoever, and kids are excited about it, the parents will be excited just to see their kids excited.

It's easy to dismiss the Exploratorium's Pi Day celebration as silly. A Pi Procession begins on 3/14 at 1:59. Everyone carries a single digit of pi, parades to music written to pi, and ends up at the museum's Pi Shrine, which they circle--you guessed it--3.14 times. Then they sing happy birthday to Albert Einstein. There is pi-lish (a form of constrained writing designed to help with the memorization of pi) and piku (Haiku written in honor of pi).

Keep laughing. No one at the Exploratorium minds, I guarantee you. Last year, they demonstrated the concept of pi with a big diagram of a pizza and let kids throw their own pi(e) crusts. Most parents had probably never seen their kids have this much fun with math, ever.

And people get way, way into it. Are you looking for evangelists for your company? The super-users? Pi Day's done it. "People show up in their favorite pi T-shirts," says Lori Lambertson, who works in the Exploratorium's teacher institute. "One woman made a skirt with pi symbols all over it. There's a couple that comes almost every year who had a baby named Pi five years ago. They'd bring baby Pi."

Who knows what they'll do next year, when the date will read 3/14/15--the first five digits of pi.

Also: Admission to the Exploratorium is free on Pi Day.

**Embrace the competition.**

All this fuss about pi has, not surprisingly, brought attention to those who think that a different number--tau--should get more of the spotlight. Tau is two times pi, but really, it's more accurate to say pi is half-tau, says Michael Hartl, a former physics instructor with Caltech, creator of the Ruby on Rails Tutorial, author of "The Tau Manifesto," and co-founder of a self-publishing platform called Softcover. "Because it involves dividing by the diameter, pi isn't the most natural choice for the circle constant," Hartl says. "It's just that it's easier to measure the diameter than the radius, but a circle is defined by its radius." Hartl says he celebrates Pi Day "ironically, as Half-Tau Day."

Hipschman is non-plussed, saying the Exploratorium used to celebrate 2Pi Day (June 28) and even 3Pi Day (September 42, or, in other words, October 12). "We invite Michael to come to Pi Day if he wishes," says Hipschman. "We'll even celebrate 2Pi with him. How's that?"

**And don't forget the pie.**

No discussion of Pi Day would be complete without a pie recipe. Barry Schuler, a much more knowledgeable cook than I, and managing director at venture fund DFJ Growth, recommends this version of *tarte tatin*. *Tarte tatin* may not technically be pie, but if you divide its circumference by its diameter you'll still get about 3.14. That's good enough for me.

Thank you, Barry, and happy eating.