Pi Day is an annual celebration that takes place on March 14th (3/14) — since 3, 1 and 4 are the three most significant digits of π in the decimal form — around the world. The first official celebration of Pi Day was organized by physicist, Larry Shaw, in 1988with staff and public marching around one of its circular spaces, then consuming fruit pies. In 2009, the United States House of Representatives supported the designation of Pi Day.

**What is Pi?**

Pi (Greek letter “π”) is the symbol used in mathematics to represent a constant — the ratio of the circumference of a circle to its diameter — which is approximately 3.14159. It has been represented by the Greek letter “π” since the mid-18th century, though it is also sometimes written as **pi**. The calculation of π was revolutionized by the development of infinite series techniques in the 16th and 17th centuries. Infinite series allowed mathematicians to compute π with much greater precision than Archimedes and others who used geometrical techniques. Although infinite series were exploited for π most notably by European mathematicians such as James Gregory and Gottfried Wilhelm Leibniz, the approach was first discovered in India sometime between 1400 and 1500 AD. ^{}

**How is Pi Day Celebrated?**

My office celebrated Pi Day today by holding a pie contest. Over 25 employees and contractors each brought in a pie and all staff was called down to the cafeteria to have a slice.

- The Massachusetts Institute of Technology (MIT) has often mailed its application decision letters to prospective students for delivery on Pi Day. Starting in 2012, MIT has announced it will post those decisions (privately) online on Pi Day at exactly 6:28 pm, which they have called “Tau Time”, to honor the rival numbers Pi and Tau equally.
- The town of Princeton, New Jersey (and home to Princeton University,) hosts numerous events in a combined celebration of Pi Day and Albert Einstein’s birthday, which is also March 14. Einstein lived in Princeton for more than twenty years while working at the Institute for Advanced Study. In addition to pie eating and recitation contests, there is an annual Einstein look-alike contest.
- Google had it’s own Pi Day doodle posted on the site in 2010.
- National Public Radio created a Pi Day rap video in 2010.

In case you missed the celebration, mark you calendar now for **Pi Approximation Day** on July 22 (or 22/7 in *day/month* date format), since the fraction ^{22}⁄_{7} is a common approximation of π. Maybe you can share a fraction of a pie with a friend.^{
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— Carole Gunst