Pi Day

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Pi Day
Significance3, 1, and 4 are the three most significant figures of π in its decimal representation.
Celebrations Pie eating, pi memorization competitions, discussions about π [1]
Date March 14
Next timeMarch 14, 2022 (2022-03-14)
First time1988
Related toPi Approximation Day

Pi Day is an annual celebration of the mathematical constant π (pi). Pi Day is observed on March 14 (3/14 in the month/day format) since 3, 1, and 4 are the first three significant digits of π. [2] [3] It was founded in 1988 by Larry Shaw, an employee of 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. [4] UNESCO's 40th General Conference designated Pi Day as the International Day of Mathematics in November 2019. [5] [6] Alternative dates for the holiday include July 22 (22/7, an approximation of π) and June 28 (6.28, an approximation of 2π or tau).



In 1988, the earliest known official or large-scale celebration of Pi Day was organized by Larry Shaw at the San Francisco Exploratorium, [7] where Shaw worked as a physicist, [8] with staff and public marching around one of its circular spaces, then consuming fruit pies. [9] The Exploratorium continues to hold Pi Day celebrations. [10]

On March 12, 2009, the U.S. House of Representatives passed a non-binding resolution (111 H. Res. 224), [4] recognizing March 14, 2009, as National Pi Day. [11] For Pi Day 2010, Google presented a Google Doodle celebrating the holiday, with the word Google laid over images of circles and pi symbols; [12] and for the 30th anniversary in 2018, it was a Dominique Ansel pie with the circumference divided by its diameter. [13]

The entire month of March 2014 (3/14) was observed by some as "Pi Month". [14] [15] In the year 2015, March 14 was celebrated as "Super Pi Day". [16] 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 10 digits of π, [17] and later that second Pi Instant represented all of π's digits. [18]


Pi Day has been observed in many ways, including eating pie, throwing pies and discussing the significance of the number π, due to a pun based on the words "pi" and "pie" being homophones in English ( /p/ ), and the coincidental circular shape of many pies. [1] [19] Also, some schools hold competitions as to which student can recall pi to the highest number of decimal places. [20] [21]

Massachusetts Institute of Technology has often mailed its application decision letters to prospective students for delivery on Pi Day. [22] 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 pi and tau equally. [23] [24] In 2015, the regular decisions were put online at 9:26 am, following that year's "pi minute", [25] and in 2020, regular decisions were released at 1:59 pm, making the first six digits of pi. [26]

June 28 is "Two Pi Day", also known as "Tau Day". 2π, also known by the Greek letter tau (𝜏) is a common multiple in mathematical formulae. Some have argued that τ is the more fundamental constant, and that Tau Day should be celebrated instead. [27] [28] Celebrations of this date jokingly suggest eating "twice the pie". [29] [30] [31]

Princeton, New Jersey, hosts numerous events in a combined celebration of Pi Day and Albert Einstein's birthday, which is also March 14. [32] 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. [32]

Alternative dates

Pi Day is most frequently observed on March 14, but related celebrations have been held on alternative dates.

Pi Approximation Day is observed on July 22 (22/7 in the day/month format), since the fraction 227 is a common approximation of π, which is accurate to two decimal places and dates from Archimedes. [33]

Two Pi Day, also known as Tau Day for the mathematical constant Tau, which is approximated as 6.28, is observed on June 28 (6/28 in the month/day format). [34]

See also

Related Research Articles

The number π is a mathematical constant. It is defined in Euclidean geometry as the ratio of a circle's circumference to its diameter, and it also has various equivalent definitions. It appears in many formulas in all areas of mathematics and physics. It is approximately equal to 3.14159. The earliest known use of the Greek letter π to represent the ratio of a circle's circumference to its diameter was by Welsh mathematician William Jones in 1706. It is also referred to as Archimedes's constant.

Greek numerals, also known as Ionic, Ionian, Milesian, or Alexandrian numerals, are a system of writing numbers using the letters of the Greek alphabet. In modern Greece, they are still used for ordinal numbers and in contexts similar to those in which Roman numerals are still used elsewhere in the West. For ordinary cardinal numbers, however, Greece uses Arabic numerals.

Error function Sigmoid shape special function

In mathematics, the error function, often denoted by erf, is a complex function of a complex variable defined as:

An approximation is anything that is intentionally similar but not exactly equal to something else.

Proofs of the mathematical result that the rational number 22/7 is greater than π (pi) date back to antiquity. One of these proofs, more recently developed but requiring only elementary techniques from calculus, has attracted attention in modern mathematics due to its mathematical elegance and its connections to the theory of diophantine approximations. Stephen Lucas calls this proof "one of the more beautiful results related to approximating π". Julian Havil ends a discussion of continued fraction approximations of π with the result, describing it as "impossible to resist mentioning" in that context.

Piphilology comprises the creation and use of mnemonic techniques to remember many digits of the mathematical constant π. The word is a play on the word "pi" itself and of the linguistic field of philology.

A mathematical coincidence is said to occur when two expressions with no direct relationship show a near-equality which has no apparent theoretical explanation.

Turn (angle) Unit of angle equal to 2𝜋 radians

A turn is a unit of plane angle measurement equal to 2π radians, 360 degrees or 400 gradians. A turn is also referred to as a cycle, revolution, complete rotation or full circle.

Pi or π is a mathematical constant equal to a circle's circumference divided by its diameter.

A Google Doodle is a special, temporary alteration of the logo on Google's homepages intended to commemorate holidays, events, achievements, and notable historical figures of particular countries. The first Google Doodle honored the 1998 edition of the long-running annual Burning Man event in Black Rock City, Nevada, and was designed by co-founders Larry Page and Sergey Brin to notify users of their absence in case the servers crashed. Subsequent Google Doodles were designed by an outside contractor until 2001, when Page and Brin asked public relations officer Dennis Hwang to design a logo for Bastille Day. Since then, a team of employees called "Doodlers" have organized and published the Doodles.

In probability and statistics, a circular distribution or polar distribution is a probability distribution of a random variable whose values are angles, usually taken to be in the range [0, 2π). A circular distribution is often a continuous probability distribution, and hence has a probability density, but such distributions can also be discrete, in which case they are called circular lattice distributions. Circular distributions can be used even when the variables concerned are not explicitly angles: the main consideration is that there is not usually any real distinction between events occurring at the lower or upper end of the range, and the division of the range could notionally be made at any point.

Viètes formula Infinite product converging to the inverse of π

In mathematics, Viète's formula is the following infinite product of nested radicals representing the mathematical constant π:

Chronology of computation of <span class="texhtml mvar" style="font-style:italic;">π</span>

The table below is a brief chronology of computed numerical values of, or bounds on, the mathematical constant pi. For more detailed explanations for some of these calculations, see Approximations of π.

Approximations of <span class="texhtml mvar" style="font-style:italic;">π</span> history of calculating π to degrees of precision

Approximations for the mathematical constant pi in the history of mathematics reached an accuracy within 0.04% of the true value before the beginning of the Common Era. In Chinese mathematics, this was improved to approximations correct to what corresponds to about seven decimal digits by the 5th century.


Milü, also known as Zulü, is the name given to an approximation to π (pi) found by Chinese mathematician and astronomer Zu Chongzhi in the 5th century. Using Liu Hui's algorithm, Zu famously computed π to be between 3.1415926 and 3.1415927 and gave two rational approximations of π, 22/7 and 355/113, naming them respectively Yuelü and Milü.

The Chudnovsky algorithm is a fast method for calculating the digits of π, based on Ramanujan’s π formulae. It was published by the Chudnovsky brothers in 1988 and was used in the world record calculations of 2.7 trillion digits of π in December 2009, 10 trillion digits in October 2011, 22.4 trillion digits in November 2016, 31.4 trillion digits in September 2018–January 2019, and 50 trillion digits on January 29, 2020.

Larry Shaw (Pi) American physicist and curator, Pi Day founder

Lawrence N. Shaw was an American physicist, curator, artist and founder of Pi Day. Shaw worked at the San Francisco science museum The Exploratorium for 33 years, performing just about every function for the museum. He was a key member of the arts and technology community in the San Francisco Bay Area.

In mathematics, Bhaskara I's sine approximation formula is a rational expression in one variable for the computation of the approximate values of the trigonometric sines discovered by Bhaskara I, a seventh-century Indian mathematician. This formula is given in his treatise titled Mahabhaskariya. It is not known how Bhaskara I arrived at his approximation formula. However, several historians of mathematics have put forward different hypotheses as to the method Bhaskara might have used to arrive at his formula. The formula is elegant, simple and enables one to compute reasonably accurate values of trigonometric sines without using any geometry whatsoever.

Emma Haruka Iwao Japanese computer scientist

Emma Haruka Iwao is a Japanese computer scientist and cloud developer advocate at Google. In 2019 Haruka Iwao calculated the world record most accurate value of pi (π); which included 31.4 trillion digits, exceeding the previous record of 22 trillion. This record was surpassed in 2020 by Timothy Mullican who calculated 50 trillion digits. She identifies as queer.


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