What is it that draws hundreds of visitors to San Francisco's Exploratorium every March to celebrate Pi Day? The allure of the unknowable? The draw of a mathematical mystery? Sure, all of that, said several participants at yesterday's event, but also the free pie.

Pi Day is celebrated on 14 March — written in the United States as 3-14, the first three digits of pi — at locales around the world. But the celebration at the Exploratorium, a hands-on science museum a stone's throw away from the Golden Gate Bridge, was the first. Maybe.

Pi Day started in 1987 or 1988, but even the originators can't quite remember when. "The origins of Pi Day are shrouded in the mystery of the 1980s," says Ron Hipschman, physicist and Exploratorium exhibit designer, who has helped design the Pi Day celebrations from year one... whenever that was.

And was the Exploratorium the first to celebrate Pi Day? Hipschman shrugs. "That's what it said in Wikipedia," he says, "so it must be true, right?"

Larry Shaw, the wild-haired official Exploratorium Pi Day founder, says the adventure began at a staff retreat, when Shaw started chatting to his co-workers about the mysteries of mathematical constants. "There are anomalies that are just curious, and pi and e are two of those," he says (with 'e' roughly equal to 2.7, Nature suggests 2 July for e-day, although there is no obvious snack to partake in).

"Nobody has a universal view of these numbers, and that leaves an opening for the imagination." Kids are good for that, Shaw notes, as he nods his head towards the dazzling brownian motion of children bouncing around the exhibit hall.

## Pie and pi-ku

“Celebrants sang Happy Birthday to Albert Einstein, who, incidentally, turned 128 on this year's pi day.”

The first Pi Day was straightforward — the staff of the Exploratorium ordered pies; the staff of the Exploratorium ate pies. The other embellishments came later. The Pi Shrine, for example — a round disk with digits winding around its edge embedded into the carpet on the second floor — didn't exist until 1989.

This year's Pi Day included: pi poetry readings, pi-kus (haikus about pi) and pi limericks; a pizza-dough tossing lesson; a demonstration of Pi Day in the virtual-reality game, Second Life; and, an unofficial prerequisite for Pi Days nearly everywhere, free pizza (as in 'pizza pie') and pie.

Promptly at 1:59 — that is, 3-14 1:59, the first six digits of pi — Shaw turns on a recording of a sing-songy computerized voice reading the digits of pi, and leads a march of Pi Day celebrants past the steam-engine display, with a left turn past the soap film exhibit, a swing around the corner at the coloured shadows demonstration, and a final ascent up the stairs to the Pi Shrine. There, celebrants sang Happy Birthday to Albert Einstein, who, incidentally, turned 128 on this year's Pi Day.

## Not just for kids

First in line after Shaw is 13-year-old Paul Rapoport, who spent years needling his mother before she finally agreed to let him make the trip from New York to San Francisco just to attend Pi Day. "She didn't want to come," he says. "I had to drag her." Rapoport is in the eighth grade but teaches himself a little calculus on the side, just for kicks. When asked whether Paul is likely to want to return to the Pi Day celebration next year, his mother rolls her eyes and winces. "I think he wants to run it," she says.

After circling the shrine, many of the celebrants return to their position in the line for free pizza. "My favourite part of Pi Day hasn't yet begun," says one, with a longing glance across the hall to where Exploratorium workers are racing to set up the free pie line.

Others stopped by a downstairs theatre to watch students from Bridge College Prep School in nearby Oakland, California, recount as many digits of pi as they could remember. Eighth grader Dakarai Lewis, who can recite 134 digits, rattles off the first few dozen digits, pauses, rattles off another couple of dozen, pauses, and finally completes his run to a round of wild applause and whoops from the audience.

Standing in the audience is 91-year-old James Stichka. Stichka, who graduated with a degree in maths from the University of California, Berkeley, in 1938, heard about Pi Day on Monday and immediately made plans to attend. "I want to meet all these kooks like me," he says with a smile. He's wearing a cardboard sign around his neck entitled "The sequence of pi" that lists a series of pie flavours, beginning with lemon meringue.

## Onwards to July

A little while later, there's a performance of a surprisingly good Einstein rap, performed by an Einstein puppet and two Exploratorium workers in white lab coats. Then the show's over, and the crowd begins to wander away while "When the Moon hits your eye / like a big pizza pie / that's amore" plays over the sound system and film clips of people getting pied continues to loop on the monitors. The Exploratorium settles back down to the normal background buzz of the museum: the pop and whir of the bicycle simulator, the occasional child's yelp or squeal. Pi Day is over.

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"We'll be back again next year," says Dennis Vozaitis of Milano Pizzeria, who ran dough-tossing demonstrations during the afternoon. "Everybody had so much fun."

Before then, of course, there is Pi Approximation Day to look forward to: 22 July (as Pi can be closely approximated by dividing 22 by 7). It may not be serious, but it is a good excuse for a party.

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