Pi Day

Larry Shaw, the founder of Pi Day, at the Exploratorium

Template:Π (mathematical constant) Pi Day and Pi Approximation Day are two unofficial holidays held to celebrate the mathematical constant $\pi$ (pi) (in the month/day format: 3/14); since 3, 1 and 4 are the first three decimal digits of π. March 14 is also the birthday of Albert Einstein and the two events are sometimes celebrated together.

Observation

Pi Approximation Day is observed on March 14, because of the Ancient Greek mathematician Archimedes' first rough approximation of π as being 3.14. (A few years later, Archimedes was able to calculate a much better approximation of π.) However, this date may be considered misleading, because 22/7 is actually a closer approximation of π than 3.14 is. Thus, a "correct" Pi Day could be found in the European calendar, 22/7, or July 22.

Sometimes the so-called Pi Minute is also commemorated. This one occurs twice on March 14 at 1:59 a.m., and 1:59 p.m. If π is truncated to seven decimal places, it becomes 3.1415926, making the Pi Second occur on March 14 at 1:59:26 p.m. (or March 14, in the year 1592 at 6:53:58 a.m.). If a 24-hour clock is used, the Pi Minute occurs just once yearly, on March 14 (3/14) at 1:59:26 in the morning.

On March 14, 2016, the date will reflect five digits of pi (3/14/16)(π≈3.1416) rather than three. The Pi Minute will be at 9:26 on that day, and the Pi Second will be at 9:26:53.

Celebration

There is a large variety of ways of celebrating Pi Day and most of them include eating pie and discussing the relevance of π. The first Pi Day celebration was held at the San Francisco Exploratorium in 1988, with staff and public marching around one of its circular spaces, then consuming fruit pies. The museum has since added pizza to its Pi Day menu. The founder of Pi Day was Larry Shaw, a now-retired physicist at the Exploratorium who still helps out with the celebrations.

The Massachusetts Institute of Technology often mails its acceptance (and rejection) letters to be delivered to prospective students on Pi Day.

Some also celebrate alternative Pi Days and/or Pi Approximation Days in addition to the two listed above; these can fall on any of several dates:

• March 4: When 14% of the 3rd month has elapsed.
• April 26: The Earth has traveled two radians of its orbit on this day (April 25 in leap years), reckoning from the start of the calendar year on January 1. The distance travelled through the entire orbit around the sun, divided by the average distance to the sun, equals 2π; two radians equals 1⁄π of our orbit. This is celebrated exactly on the 41st second of the 23rd minute of the 4th hour on April 26 or the 116th day. (In leap years, it is celebrated exactly on the 3rd second of the 2nd minute of the 12th hour on April 25 or the 116th day.) This celebration is not a Pi Approximation Day.
• July 22: written in the European date format as 22/7, an approximate value of pi.
• November 10: The 314th day of the year (November 9 in leap years).
• December 21, 1:13 p.m.: The 355th day of the year (December 20 in leap years), celebrated at 1:13 for the Chinese approximation 355/113.

History

On Pi Day 2004, Daniel Tammet recited 22,514 decimal digits of π.

On 12 March 2009, the U.S. House of Representatives passed a non-binding resolution (HRES 224), recognizing March 14, 2009 as National Pi Day.

On March 14, 2010, Google made a Google Doodle celebrating Pi Day, with the word Google laid over images of circles and pi symbols.

Pi pies

Pi Day is often celebrated with pies, given that pi and pie are homonyms.

Gallery

• 
  Pies for a celebration at the Massachusetts Institute of Technology
• 
  Pi Pie at Delft University
• An Apple PI at Ss. Cyril and Methodius University
  An Apple PI at Ss. Cyril and Methodius University
• 
  Free pies being prepared at the University of Waterloo

External links

• Exploratorium's Pi Day Web Site
• NPR provides a "Pi Rap" audiovideo