Pi Day is an annual celebration commemorating the mathematical constant π (pi). Pi Day is observed on March 14 (or 3/14 in the month/day date format), since 3, 1, and 4 are the first three significant digits of πin decimal form. In 2009, the United States House of Representatives supported the designation of Pi Day.
The earliest known official or large-scale celebration of Pi Day was organized by Larry Shaw in 1988 at theSan 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.
In the year 2015, Pi Day will have special significance on 3/14/15 at 9:26:53 a.m. and p.m., with the date and time representing the first 10 digits of π. That same second will also contain a precise instant corresponding to all of the digits of π.
Observance of Pi Day has been observed in many ways, including eating pie, throwing pies and discussing the significance of the number π.