Pi Day

Pi Day is an unofficial holiday commemorating the mathematical constant ? (pi). Pi Day is observed on March 14 (or 3/14 in month/day date format), since 3, 1 and 4 are the three most significant digits of ? in the decimal form. In 2009, the United States House of Representatives supported the designation of Pi Day.
Pi Approximation Day is observed on July 22 (or 22/7 in day/month date format), since the fraction 22/7 is a common approximation of ?.

History

The earliest known official or large-scale celebration of Pi Day was organized by Larry Shaw in 1988 at the San Francisco Exploratorium, where Shaw worked as a physicist, with staff and public marching around one of its circular spaces, then consuming fruit pies. The Exploratorium continues to hold Pi Day celebrations.
On March 12, 2009, the U.S. House of Representatives passed a non-binding resolution (HRES 224), recognizing March 14, 2009, as National Pi Day.
For Pi Day 2010, Google presented a Google Doodle celebrating the holiday, with the word Google laid over images of circles and pi symbols.

Pi Day is observed on March 14 because of the date's representation as 3/14 in month/day date format. This representation adheres to the commonly used approximation of 3.14 for ?.
The fractional approximation of ?,22/7, resembles the date July 22 in the day/month format, where it is written 22/7. Pi Approximation Day is therefore observed on July 22.

Observance

There are many ways of observing Pi Day. These include eating pie and discussing the significance of the number ?.
The Massachusetts Institute of Technology 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 6:28pm, which they have called 'Tau Time', to honor the rival numbers Pi and Tau equally.
The town of Princeton, New Jersey 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.