From San Francisco to New York, in museums, universities, classrooms and in the privacy of one's own home, (and of course on Second Life), people are celebrating Pi. It's the 21st anniversary of the celebration of Pi Day, an international holiday born at San Francisco's Exploratorium. The number is Pi, 3.1415926535...ad infinitum. It's today's date and the starting time, the number you get when you divide the circumference of a circle by its diameter, and it cannot be expressed as a fraction. It continues forever. In an era when math and mathematicians have become sexy again, it's worth recounting how Pi Day came to be and why it is that people still go to the Exploratorium and gather around the Pi Shrine to perform pi-related rites and eat ritual food -- be it apple pie or pizza pie -- in honor of this special number. People sing Pi Day songs, bead a pi string (a physical manifestation of the never ending value of pi), and circumnavigate a pi shrine. Pi Day celebrations culminate, appropriately enough, on March 14 at 1:59pm. That's the third month, the fourteenth day, at 1:59pm, corresponding to the first 6-digits of Pi. And as an added bonus, 3/14 is also Einstein's birthday.

The original Pi guy is Larry Shaw, a physicist with streaming white hair, a white beard and a transcendent glow. It was 1987, and a cacophony of cultural references and relationships of the time intersected in San Francisco at the Exploratorium, to this day an internationally acclaimed museum of science, art and human perception. Shaw was thinking a lot about the concept of rotation into another dimension -- the sorts of things he was actually paid to do. To recapture the time and the place, imagine Shaw mulling over the metaphor of the Hitchhiker's Guide to the Galaxy, specifically the infinite improbability drive of the Heart of Gold Space Ship that is a major factor in the book. Turns out that the concept of rotation into another dimension is exactly what Pi describes. Pi represents the relationship between one dimension to another in the sense of the linear dimension and the plane; or the relation of the linear dimension and the sphere. Pi is key to these relationships. So for Shaw, Pi was in the air and definitely on his mind. He and his colleagues were talking about a Pi Shrine or a Pi Day, something to make the concept of rotation noteworthy. And so it all came together. For the first Pi Day, they installed a Pi Shrine (a small brass plate engraved with pi to a hundred digits) at the exact center of a circular Exploratorium classroom, a spot that also corresponds to the center-line of the museum's building. And they walked around the shrine because as Shaw notes, "People go around things to show respect to them in many cultures and religions." And they ate pie.

It wasn't until 1989 at the 3rd Pi Day, that the overlap with Einstein's birthday was uncovered by Shaw's 14-year-old daughter Sara, who is, today, a veterinarian. She was writing a report on Einstein and told her dad that his Pi Day -- 3/14 -- was also Einstein's birthday. Voila. With all that mathematical kismet going for it, Pi Day gradually took on an international life of its own.

On 3/14/08, at 1:59pm at the Exploratorium, Larry Shaw will be on hand as celebrants from the general public come to circumambulate the Pi shrine approximately 3.14 times, since 3.14 is an approximation of Pi. They will add yet more beads representing the numbers 0-9 to a ritual pie string, where each color bead designates a value for Pi to over 1600 digits, and growing. Music based on the number Pi provides the ambience.

Pi Day is included in the price of admission to the Exploratorium. Pi Day also takes place in the Second Life version of the Exploratorium, known as the 'Splo.