View source for Pi Day

== Alternative dates ==
Pi Day is frequently observed on March 14 (3/14 in the ''month/day'' date format, favoured by the USA), 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 (mathematics)|fraction]] {{frac|22|7}} is a common [[Approximations of π|approximation of {{pi}}]], which is accurate to two decimal places and dates from [[Archimedes]].<ref name="VerizonTodayInHistory">{{Cite web |title=Pi Approximation Day is celebrated today |url=http://www.thinkfinity.org/2010-07-22_pi-approximation-day |archive-url=https://web.archive.org/web/20101201010400/http://www.thinkfinity.org/2010-07-22_pi-approximation-day |archive-date=December 1, 2010 |access-date=January 30, 2011 |website=Today in History |publisher=Verizon Foundation}}</ref>

'''Tau Day''', also known as '''Two-Pi Day''',<ref>{{Cite web |url=https://newsroom.lamresearch.com/Celebrating-Pi-Day-2017-and-More |title=Celebrating Pi Day 2017… and More! |first=Elizabeth |last=Pavel |date=March 13, 2017 |publisher=[[Lam Research]] |access-date=6 November 2024 |archive-url=https://web.archive.org/web/20230330164730/http://newsroom.lamresearch.com/Celebrating-Pi-Day-2017-and-More |archive-date=March 30, 2023 |url-status=live}}</ref> is observed on [[June 28]] (6/28 in the ''month/day'' format).<ref name="lightyears">{{Cite web |title=Tau Day: Why you should eat twice the pie |url=https://lightyears.blogs.cnn.com/2012/06/28/tau-day-why-you-should-eat-twice-the-pie/ |url-status=dead |archive-url=https://web.archive.org/web/20130112211136/http://lightyears.blogs.cnn.com/2012/06/28/tau-day-why-you-should-eat-twice-the-pie/ |archive-date=January 12, 2013}}</ref> The number [[Tau (mathematical constant)|{{tau}}]], denoted by the Greek letter [[tau]], is the ratio of a circle's [[circumference]] to its [[radius]]; it equals 2{{pi}}, a common multiple in mathematical formulae, and approximately equals 6.28. Some have argued that {{tau}} is the clearer and more fundamental constant and that Tau Day should be celebrated alongside or instead of Pi Day.<ref>{{Cite news |date=March 13, 2018 |title=It's Pi Day today. But these people say we should refuse to celebrate it |language=en-GB |work=The Independent |url=https://www.independent.co.uk/news/science/pi-day-march-14-maths-google-doodle-pie-baking-celebrate-30-anniversary-a8254036.html |url-status=live |url-access=subscription |access-date=March 14, 2018 |archive-url=https://ghostarchive.org/archive/20220526/https://www.independent.co.uk/news/science/pi-day-march-14-maths-google-doodle-pie-baking-celebrate-30-anniversary-a8254036.html |archive-date=May 26, 2022}}</ref><ref>{{Cite news |date=March 14, 2013 |title=Pi Day Turns 25: Why We Celebrate an Irrational Number |url=https://news.nationalgeographic.com/news/2013/03/031314-pi-day-exploratorium-mathematics-pie-science/ |archive-url=https://web.archive.org/web/20130314185319/http://news.nationalgeographic.com/news/2013/03/031314-pi-day-exploratorium-mathematics-pie-science/ |url-status=dead |archive-date=March 14, 2013 |access-date=March 14, 2018}}</ref><ref>{{Cite web |last=BMJ |date=June 22, 2018 |title=Jeffrey Aronson: When I use a word ... The Days of Pi |url=https://blogs.bmj.com/bmj/2018/06/22/jeffrey-aronson-when-i-use-a-word-the-days-of-pi/ |access-date=May 2, 2023 |website=The BMJ |language=en-US}}</ref> Celebrants of this date jokingly suggest eating "twice the pie".<ref>{{Cite book |last=Bartholomew |first=Randyn Charles |url=https://www.scientificamerican.com/article/let-s-use-tau-it-s-easier-than-pi/ |title=Why Tau Trumps Pi |language=en}}</ref><ref>{{Cite news |last=Landau |first=Elizabeth |title=In case Pi Day wasn't enough, it's now 'Tau Day' on the Internet |language=en |work=CNN |url=http://www.cnn.com/2011/TECH/innovation/06/28/tau.day.math/index.html}}</ref><ref>{{Cite web |title=Tau Day – Come Eat Twice the (Pi)e |url=https://www.geocaching.com/geocache/GC56WHN_tau-day-come-eat-twice-the-pie?guid=19c50aa3-fe1c-4961-8df8-f03f3798de91 |language=en}}</ref>

Some also celebrate {{pi}} on [[November 10]], since it is the 314th day of the year (in leap years, on [[November 9]]).<ref>{{Cite web |title=Pi Day – Fun Holiday |url=https://www.timeanddate.com/holidays/fun/pi-day |access-date=March 13, 2022 |publisher=Timeanddate.com}}</ref>