Pi Day - March 14, the math celebration

Pi Day on March 14 (3/14) celebrates the mathematical constant pi (\u03c0 \u2248 3.14159). Observed informally worldwide with math-themed events, pie-eating contests, and educational programming. Not a public holiday.

The one-line summary

Informal observance on March 14, founded in 1988 by the Exploratorium. Cultural category, minor tier.

Origin

Pi Day was founded in 1988 by Larry Shaw, a physicist at the Exploratorium science museum in San Francisco. Shaw organised the first Pi Day celebration on March 14, 1988, and led annual celebrations at the museum until his death in 2017.

The choice of March 14 (3/14) is anchored on the first three digits of pi. The day is observed informally with math-themed events, pie-eating contests, and educational programming. The US House of Representatives passed a non-binding resolution recognising Pi Day in 2009.

When it falls

March 14, every year. Pi Day is a fixed Gregorian date and does not move. Pi Approximation Day on July 22 is the alternative date using the fraction 22/7.

How it is observed

Math and science museums host pi-themed events. Schools run pi-recitation contests, pie-eating contests, and pi-themed lesson plans. Universities host pi-day lectures. The Exploratorium in San Francisco hosts an annual pi parade; the Massachusetts Institute of Technology releases its admissions decisions on Pi Day.

Regional variations

Pi Day is observed informally worldwide. The largest organised events are in the United States (Exploratorium and MIT), with growing observance in the United Kingdom, Canada, and Australia. European observance is less prominent; the day is celebrated informally by math teachers and enthusiasts.

Legal status

Pi Day is not a public holiday in any country. The US House of Representatives resolution in 2009 was symbolic. Schools, museums, and universities use the day for educational programming.

Pi Day by the numbers

Sources

• Exploratorium (San Francisco), Pi Day history and annual events.
• US House of Representatives Resolution 224, March 2009 (Pi Day).
• Massachusetts Institute of Technology, Pi Day admissions tradition.

What is pi

Pi (π) is the ratio of a circle's circumference to its diameter. The value is approximately 3.1415926535 8979323846 2643383279 5028841971 6939937510 5820974944 5923078164 0628620899 8628034825 3421170679 ... Pi is irrational (its decimal expansion never terminates or repeats) and transcendental (no polynomial with rational coefficients has it as a root). The first proof of irrationality is by Johann Lambert (1761); the transcendence proof is by Ferdinand von Lindemann (1882). Pi's irrationality is the reason March 14 (3/14) was chosen as Pi Day - 3.14 truncated.

Pi has been calculated to more than 100 trillion decimal digits (2022, Emma Haruka Iwao at Google Cloud). Practical applications rarely require more than 40 digits. NASA uses 15 digits for interplanetary navigation; CERN uses 32 digits for accelerator design.

History of the symbol π

The Greek letter π was first used for the constant in 1706 by Welsh mathematician William Jones, in his Synopsis Palmariorum Matheseos. Earlier writers used the English word "periphery' or the alternative notation "quantitas, in quam cum multiflicetur diameter, provenit circumferentia'. The symbol became standard after Leonhard Euler used it in 1737, and Euler's later works cemented it as the global convention.

Before the symbol, Archimedes (c. 250 BC) proved the bounds 3 10/71 < π < 3 1/7 using inscribed and circumscribed polygons. Zu Chongzhi of China (c. 480 AD) calculated π to seven decimal places (3.1415926 to 3.1415927), which held as the most accurate known value for nearly 1,000 years until the 1420s.

Pi Day traditions

Pi Day has been celebrated by the Exploratorium in San Francisco since 1988, founded by physicist Larry Shaw. The 2009 US House Resolution 224 designated March 14 as National Pi Day (though it is not a federal holiday). MIT announces admissions decisions at 6:28 PM (pi minutes) on Pi Day each year. The practice of "pie eating' - a pun on the homophone - is documented as early as the 1988 Exploratorium events.

Outside the US, Pi Day is observed informally in the UK, France, Germany, Japan, Australia, and many other countries with strong science-communication communities. The United Nations UNESCO International Day of Mathematics is on March 14 (Pi Day), adopted in 2019 at the 40th General Conference. The UN day and the US Pi Day are typically observed together on March 14 each year.

Pi approximation records

Pi approximation contests are a perennial Pi Day feature. The most-cited early record is Akria Haraguchi of Japan, who recited 100,000 digits from memory in 2006 (the previous Guinness-certified record). Suresh Kumar Sharma of India recited 70,030 digits in 2015. Rajveer Meena of India recited 70,000 digits in 2015 (University of Technology, Vellore), a Guinness-certified record. The longest verified recitation is held by Chao Lu of China, who recited 67,890 digits in 24 hours and 4 minutes in 2005.

Pi in popular culture

The 1998 film "Pi' by Darren Aronofsky dramatised a mathematician's descent into numerical obsession. The 2012 film "Life of Pi' (Ang Lee) is a different reference. The musical composition "Pi' by Michael Blake (1992) sets the first 31 digits of pi to music. "Pi Day Pie" - a circular pie baked to honour Pi Day - is the most-photographed food observance of any science day.

History of Pi Day

Pi Day is celebrated on March 14 (3/14), reflecting the first three digits of the mathematical constant pi (π = 3.14159...). Pi Day was founded in 1988 by Larry Shaw, a physicist at the Exploratorium science museum in San Francisco. Pi Day has since gained international recognition, with the US House of Representatives passing a resolution in 2009 recognising March 14 as National Pi Day.

How Pi Day is celebrated

Pi Day is celebrated with math competitions, pie-eating contests (a pun on the homophone of pi and pie), educational events, and social media campaigns. Schools often host Pi Day events in math classes. Some celebrations extend to Pi Minute (3:14 PM) or Pi Second (3:14:15 PM).

Pi Day has also been promoted as an opportunity to discuss the role of mathematics in everyday life and to encourage students to pursue STEM education. The Exploratorium's annual Pi Day celebration remains one of the largest, with participants marching in circles (referencing the geometry of circles) and eating pie.

Pi facts

A few facts about the mathematical constant pi (π):

• Pi is irrational, meaning it cannot be expressed as a ratio of two integers.
• Pi is also transcendental, meaning it is not the root of any polynomial equation with rational coefficients.
• Pi has been calculated to more than 100 trillion digits.
• The Greek letter π was first used to denote the constant by Welsh mathematician William Jones in 1706.
• The earliest known approximations of pi date to ancient Babylon and Egypt.