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# Celebrate 25 years of Pi Day

The most famous irrational number, pi, is being factored into a whole smorgasbord of silliness on 3/14.On one level, the date is just an excuse for high geekery, ranging from eating mathematically meaningful pies to marching in a circular pi procession. On a deeper level ... well, who needs an excuse to celebrate one of nature's most mysterious numbers?

The most famous irrational number, pi, is being factored into a whole smorgasbord of silliness on 3/14.

On one level, the date is just an excuse for high geekery, ranging from eating mathematically meaningful pies to marching in a circular pi procession. On a deeper level ... well, who needs an excuse to celebrate one of nature's most mysterious numbers?

In differently curved universes, the ratio of a circle's circumference to its diameter might be something other than 3.14159 and some change. But in our universe, the digits that describe that ratio have never come to an end or shown a repeating pattern, even though pi's value has been computed to a length of 10 trillion digits. The irrationality of pi has popped up as a theme in a goodly number of books and movies through the years, including "Contact" (the book) and "Pi" (the movie). Pi's continuing hold on our imagination is definitely something worth celebrating.

Here are a few ways to mark the day:

• Celebrate the 25th Pi Day with the Exploratorium in San Francisco, where the festivities reach their peak at 3/14, 1:59 p.m. PT. The Exploratorium in San Francisco is where it all began in 1988, when physicist Larry Shaw organized the first public celebration of Pi Day. There'll also be a Pi Day party on Exploratorium Island in the Second Life virtual world, starting at 8 p.m. PT / SLT.
• Send a Pi Day e-card. The Web site for Pi Day offers discussions and videos about pi, books and merchandise to buy, suggested activities and information about the why of pi.
• Look around for local events, such as Pi Day Princeton or the Maryland Science Center's Pi Day party. Chances are that your local science center is doing something to celebrate the day ... and if not, maybe you can convince the ticket-takers to reduce the cost of admission to \$3.14, just this once.
• Celebrate Albert Einstein's birthday, which also falls on March 14. Our "Century of Einstein" special report is just as insightful today as it was when we published it in 2005 to mark the centennial of the great physicist's "miracle year."
• Make your plans for Tau Day, the holiday for people who think pi is passé. Tau is twice the value of pi, and some mathematicians say that makes their equations easier to juggle. If you're a tau touter, June 28 (6/28) is your special day. And if you don't follow the American style of stating dates, you might be more comfortable celebrating pi on July 22 (22/7), a date that evokes a fraction close to the irrational value of pi.

Anything to add? If you have other ways to celebrate Pi Day, let us know in your comment below.

More pi peculiarity:

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.