Pi Day

Template:Short description Template:Distinguish Template:Use American English Template:Use mdy dates Template:Infobox holiday Template:Pi box Pi Day is an annual celebration of the mathematical constant [[pi|Template:Pi (pi)]]. Pi Day is observed on March 14 (the 3rd month) since 3, 1, and 4 are the first three significant figures of Template:Pi, and was first celebrated in the United States.<ref>Template:Cite web</ref><ref>Template:Cite web</ref> It was founded in 1988 by Larry Shaw, an employee of a science museum in San Francisco, the Exploratorium. Celebrations often involve eating pie or holding pi recitation competitions. In 2009, the United States House of Representatives supported the designation of Pi Day.<ref name="HORRes">United States. Cong. House. Supporting the designation of Pi Day, and for other purposes. 111th Cong. Library of Congress Template:Webarchive</ref> UNESCO's 40th General Conference designated Pi Day as the International Day of Mathematics in November 2019.<ref>Template:Cite web</ref><ref>Template:Cite journal</ref>

Other dates when people celebrate pi include Pi Approximation Day on July 22 (22/7 in the day/month format), another [[Approximations of π|approximation of Template:Pi]]; and June 28 (6.28), an approximation of 2Template:Pi or [[Tau (mathematical constant)|Template:Tau]] (tau).

History

In 1988, the earliest known official or large-scale celebration of Pi Day was organized by Larry Shaw at the San Francisco Exploratorium,<ref>Template:Cite web</ref> where Shaw worked as a physicist,<ref name="ABC – Science – 10 Mar 2011 – infinite appeal of pi">Template:Cite web</ref> with staff and public marching around one of its circular spaces, then consuming fruit pies.<ref name="fresnobee">Template:Cite news</ref> The Exploratorium continues to hold Pi Day celebrations.<ref name="exploratorium">Template:Cite web</ref>

On March 12, 2009, the U.S. House of Representatives passed a non-binding resolution (111 H. Res. 224),<ref name="HORRes" /> recognizing March 14, 2009, as National Pi Day.<ref>Template:Cite news</ref> For Pi Day 2010, Google presented a Google Doodle celebrating the holiday, with the word Google laid over images of circles and pi symbols;<ref name="GoogleDoodle">Template:Cite web</ref> and for the 30th anniversary in 2018, it was a Dominique Ansel pie with the circumference divided by its diameter.<ref>Template:Cite web</ref>

Some observed the entire month of March 2014 (3/14) as "Pi Month".<ref>Template:Cite magazine</ref><ref>Template:Cite web</ref> In the year 2015, March 14 was celebrated as "Super Pi Day".<ref>Template:Cite web</ref> It had special significance, as the date is written as 3/14/15 in month/day/year format. At 9:26:53, the date and time together represented the first ten digits of Template:Pi,<ref>Template:Cite web</ref> and later that second, "Pi Instant" represented all of Template:Pi's digits.<ref>Template:Cite journal</ref>

Observance

File:Happy Pi Day sign for sales on pies at Delicious Orchards.jpg

Pi Day related offering at Delicious Orchards, a country food market in Colts Neck, New Jersey

Pi Day has been observed in many ways, including eating pie, throwing pies and discussing the significance of the number Template:Pi.<ref>Template:Cite news</ref> The first two are due to a pun based on the words "pi" and "pie" being homophones in English (Template:IPAc-en), and the coincidental circular shape of many pies.<ref name="landau" /><ref>Template:Cite web</ref> Many pizza and pie restaurants offer discounts, deals, and free products on Pi Day.<ref name="nbcdfw">Template:Cite news</ref> Also, some schools hold competitions as to which student can recall pi to the highest number of decimal places.<ref>Template:Cite web</ref><ref>Template:Cite web</ref>

The Massachusetts Institute of Technology has often mailed its application decision letters to prospective students for delivery on Pi Day.<ref>Template:Cite news</ref> 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 Template:Pi and Template:Tau equally.<ref>Template:Cite web</ref><ref>Template:Cite web</ref> In 2015, the regular decisions were put online at 9:26 am, following that year's "pi minute",<ref>Template:Cite web</ref> and in 2020, regular decisions were released at 1:59 pm, making the first six digits of pi.<ref>Template:Cite web</ref>

Princeton, New Jersey, hosts numerous events in a combined celebration of Pi Day and Albert Einstein's birthday, which is also March 14.<ref name="princeton">Template:Cite web</ref> 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.<ref name="princeton" />

In 2024, the recreational mathematician Matt Parker and a team of hundreds of volunteers at City of London School spent six days calculating 139 correct digits of pi by hand, in what Parker claimed was "the biggest hand calculation in a century".<ref name="Piday2024">Template:Cite AV media</ref><ref>Template:Citation</ref> On 15 August 2024, the main-belt asteroid 314159 Mattparker Template:Efn was named in his honor. The citation highlights Parker's biennial "Pi Day challenges", stating that they have helped to popularize mathematics.<ref name="asteroid">Template:Cite journal</ref><ref name="Piday2011">Template:Cite news</ref>

Alternative dates

File:22 Divided by 7 Circle.png

Pi Approximation Day is often observed on July 22 (22/7), though this circle is not perfect at illustrating pi.

Pi Day is frequently observed on March 14 (3/14 in the month/day date format), but related celebrations have been held on alternative dates.

Pi Approximation Day is observed on July 22 (22/7 in the day/month date format), since the fraction Template:Frac is a common [[Approximations of π|approximation of Template:Pi]], which is accurate to two decimal places and dates from Archimedes.<ref name="VerizonTodayInHistory">Template:Cite web</ref> In Indonesia, a country that uses the DD/MM/YYYY date format, some people celebrate Pi Day every July 22.<ref>Template:Cite book</ref>

Tau Day, also known as Two-Pi Day,<ref>Template:Cite web</ref> is observed on June 28 (6/28 in the month/day format).<ref name="lightyears">Template:Cite web</ref> The number [[Turn (angle)#Tau proposals|Template:Tau]], denoted by the Greek letter tau, is the ratio of a circle's circumference to its radius; it equals 2Template:Pi, a common multiple in mathematical formulae, and approximately equals 6.28. Some have argued that Template:Tau is the clearer and more fundamental constant and that Tau Day should be celebrated alongside or instead of Pi Day.<ref>Template:Cite news</ref><ref>Template:Cite news</ref><ref>Template:Cite web</ref> Celebrants of this date jokingly suggest eating "twice the pie".<ref>Template:Cite book</ref><ref>Template:Cite news</ref><ref>Template:Cite web</ref>