Middle-school students celebrate Pi Day a few years back with defense contractor… (Raytheon )

Happy Pi Day!

March 14 -- a.k.a. 3.14 -- has become a day to appreciate the wonders of pi. This mathematical constant describes the ratio of a circle’s circumference to its diameter. It’s also handy for calculating a circle’s area, along with plenty of other uses in the fields of trigonometry, physics, statistics, cosmology and fluid dynamics, to name just a few.

Humans have been contemplating pi for nearly 4,000 years. The ancient Babylonians figured out that pi’s value was roughly 3 as far back as 1900 BC. The ancient Greek mathematician Archimedes figured out that pi was slightly bigger than 22/7. Today, it is commonly taught in schools as 3.14, though enthusiasts can take the number out to as many decimal places as they’d like. So far, computers have calculated 10 trillion digits.

Larry Shaw, a physicist at the Exploratorium science museum in San Francisco, is credited with creating Pi Day in 1988. This year, the museum will host a Pi Parade and serve pie to visitors (in years past, they’ve had pizzas). Pi partisans who can’t be there in person may participate virtually through Second Life.

In my book, the No. 1 way to mark the day is with a slice of cherry pie a la mode. But there are slightly more cerebral ways to celebrate, including:

* Search for your birthday -- or Social Security number or ZIP Code -- among the first 200 million digits of pi. (My own birth date appeared twice.) A search engine can look for any number up to 120 digits long.

* Calculate pi on your iPhone or iPad. Yes, there’s an app for that -- and it’s free. In 1949, it took the ENIAC, the world’s first electronic computer, an entire 70 hours to calculate pi out to 2,037 digits. Now your can do it on a device that fits in your pocket.

* Send an e-card. There are several to choose from here.

* Watch this three-minute, 14-second video of a very patient soul who built a huge pi out of dominoes.

* Appreciate this sight gag. It’s not quite a palindrome, but if you take the number 3.14 and hold it up to a mirror, you might be surprised by what you’ll see.

* Find out if you got into MIT. The admissions office posts its decisions on freshman applicants on Pi Day. If you think this is cool, this is the school for you. (Pi also makes an appearance in one of MIT’s cheers: “... Cosine, secant, tangent, sine/ 3.14159 ...”)

By the way, March 14 is also Albert Einstein’s birthday -- he would have been 134 years old today.

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