*[Editor: On Pie Day today, we bring back one of our timeless articles from our archives]*

Now, here's a day to celebrate those delicious circular apple and plum pies. March 14 (3/14) every year is celebrated as Pi Day by both mathematicians and food lovers around the world!

Pi represents an irrational number that begins with 3.141592653 and continues indefinitely. It is used to compute the area, circumference, and volume of circles. In fact, it has been calculated for up to 2 trillion digits, and the beauty is the numbers never repeat!

Pi day is marked in many ways - from competitions on how many digits students can memorize to pie-eating contests. Even companies join in the fun. Raytheon sends out pies to math teachers at schools within 3.14 miles of its company offices!

**The Origin Of Pi**

Circles have always puzzled ancient mathematicians. Even as early as 1900 BC, various civilizations from Babylonia to Greece and India had discovered that the circumference of a circle is always a little more than three times the diameter of the circle. There was no precise value that was available as each civilization computed the ratio within 1% of its actual value.

Archimedes is said to have finally figured it out and named the value 'Pi'. He realized that rather than working with circles he could use polygons. So he began comparing the perimeters of two polygons – one inscribed inside a circle and the other outside. By comparing over 96 such polygons, Archimedes arrived at the value 3.14159. The more sides in a polygon, the better the value of pi. The value that Archimedes computed was still only 99.9% accurate.

Mathematicians have figured that the value of Pi can be arrived at using the ratio (22/7). In honor of this constant, some people celebrate Pi approximation day as July 22!

**Albert Einstein & 'Pi'**

Physics and mathematics go hand in hand. So what better way than to celebrate both on the same day! March 14 also happens to be the birthday of Albert Einstein - the famous theoretical physicist who gave us the "Theory of Relativity". We had written about Einstein here. Princeton University, where Einstein spent 22 years of his life, hosts a day-long celebration, a walking tour of the neighborhood where he lived, and Einstein look-alike contests!

In 1988, San Francisco Exploratorium was the first to hold a Pi Day Celebration. Larry Shaw, a retired physicist is credited with its founding. In 2009, the United States House of Representatives passed a resolution to support naming March 14 (3/14) as Pi Day.

This Pi Day, as you chomp down those round delicacies, spare a thought for the math behind it!