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MonJul 22

Pi Approximation Day – July 22, 2024

Pi or pie, whether you’re a baker or a math whiz, today is your day — Pi Approximation Day on July 22 honors the concept of pi, which is denoted by the Greek letter pi and approximates to 3.14, in the most mathematically-pleasing way. To further make punny jokes out of pi day, many bake pies on the holiday. It’s a great day to appreciate the math concept used so regularly in many calculations, and eat some delicious pie!

History of Pi Approximation Day

Pi has been known for nearly 4000 years in some form or another. Ancient Babylonians used it — approximated to 3.125, to calculate the dimensions of circles. It was around 250 B.C. that pi was first calculated by one of the greatest ancient mathematicians, Archimedes of Syracuse. He found that pi fell somewhere between 3 1/7 and 3 10/71. Pi is occasionally referred to as the ‘Archimedes’ Constant.’

Later, in the mid-400s, another brilliant mathematician, Zu Chongzhi, computed pi again with lengthy calculations. Since Archimedes’ books were lost, and not in China at that time, Zu calculated pi himself in a novel way. Between Zu and Archimedes, these two scientists were the first to know pi in any true sense.

Later, mathematicians attempted to better approximate pi using circumscribed and inscribed polygons. This was how Archimedes first solved for pi, and it remained the dominant algorithm for pi computation for 1,000 years. The most correct approximation achieved using this method came in 1630, with Austrian astronomer Christoph Grienberger, who arrived at 38 correct digits of pi.

With the development of the infinite series (the sum of the terms of an infinite sequence) in the 16th- and 17th centuries, the way pi was calculated was revolutionized. In India, they discovered it early, between 1400 and 1500 A.D., yet it’s European mathematicians like Leibniz and Gregory who popularized it a century later. Though pi was a well-known concept for centuries, it wasn’t until 1706 that the Greek symbol pi came to represent it. This was suggested by William Jones, a Welsh mathematician, but not popularized until it was used by Leonhard Euler in 1737.

In modern times, endless amounts of computing power have been dedicated to approximating the infinite, irrational number to the fullest extent possible. The first time pi was computed by a machine was in 1957, when George Reitwiesner and John von Neumann used an ENIAC computer to compute 2,037 digits of pi. Many intrepid mathematicians followed. By 1973, a million digits were reached with this method.

The calculation of pi became a useful stress test for a computer’s abilities — almost like a test for the heart. Mathematicians also hoped to have more accurate calculations for pi for cosmology, though, for most pursuits, few digits are needed. Emma Haruka Iwao, a Google employee who calculated more digits of pi than anyone else to this point — 31 trillion, has earned a place in the Guinness Book of World Records.

Pi Approximation Day timeline

250 B.C.
First Pi Calculation

Performed by Archimedes of Syracuse, the first pi calculation showed that the number fell somewhere between 3 1/7 and 3 10/71.

First Pi Calculation

Performed by Archimedes of Syracuse, the first pi calculation showed that the number fell somewhere between 3 1/7 and 3 10/71.

Euler Popularized Pi

While pi, the Greek letter representing 22/7, had been introduced to mathematics in 1706 and subsequently accepted, it was not popularized until 1737, when Leonhard Euler adopted it.

Computing Pi

For the first time, pi was computed with a computer, using an ENIAC computer to calculate 2,037 digits of pi.

September, 2010
A Thousand Computers of Pi

With the help of Yahoo!’s Hadoop application, one employee used 1,000 computers to get to the two-quadrillionth bit of pi.

Pi Approximation Day FAQs

Where is Pi Approximation Day celebrated?

The United States.

Why is Pi Approximation Day celebrated?

Pi Approximation Day is on July 22 and is dedicated to the infinite constant pi(π). The holiday is also known as Casual Pi Day. 

Who found pi?

The first calculation of pi was carried out by one of the greatest mathematicians of the time, Archimedes of Syracuse (287-212 B.C.).

Pi Approximation Day Activities

  1. Bake some pi(e)

    Many bakers find Pi Approximation Day the perfect, punny excuse to whip up a pie. Many of the Pi Approximation Day pies even feature pi, the Greek letter, as a decoration on top!

  2. Memorize pi

    One of the most notable features of pi is that it is infinite. It continues indefinitely without any pattern or repetition, making it both a transcendental and irrational number. Schoolchildren and mathematicians alike find it a fun challenge to memorize as many digits of the number as they can! Challenge a friend or family member to beat your knowledge of pi today.

  3. Celebrate mathematics

    At its core, Pi Approximation Day is a celebration of all the math that pi has allowed us to do. It is essential for the basic calculation of the circumference of a circle, but even NASA also uses pi in a variety of ways, like calculating spacecraft trajectories! Pi is an essential constant for some of the most important math we know.

5 Fun Facts About Pi

  1. We’ll never know the true area of a circle

    Though you’ve been calculating the area and circumference of a circle with pi since elementary school, you’ll actually never know the exact measurements since we’ll never know pi!

  2. 70,000 digits have been memorized

    Achieved by a student, Rajveer Meena of VIT University, the record for most digits of pi memorized and recited is 70,000 — the recitation took 10 hours!

  3. The pyramids were built with pi

    Believe it or not, pi was a part of Ancient Egyptian mythology — the people built their wondrous pyramids using the principles of pi.

  4. We know more than 30 trillion digits

    Though pi can never be fully calculated, mathematicians have set computers to work to calculate as many decimals of pi as possible — these days, we’re up to over 31 trillion digits.

  5. Pi has been pi for 250 years

    First used by Welsh mathematician William Jones in 1706, the greek symbol for pi (π) took the place of the old, clunky identifier: “the quantity which when the diameter is multiplied by it, yields the circumference.”

Why We Love Pi Approximation Day

  1. Pi is infinitely cool

    Pi (π) is the ratio of a circle’s circumference to its diameter — and, amazingly, for all circles of any size, pi will always be the same. Pi is an ‘irrational number,’ meaning its exact value is completely unknown. Scientists have calculated billions of digits starting with 3.14159265358979323…, but no recognizable pattern ever emerges. We could continue on and on until infinity and we'd still have no idea what digit might emerge next.

  2. Pi sounds like pie

    If you are a nerd that likes pies, this holiday is pretty much the best combination of some of the best things in life: pie and mathematics. And, of course, that means that in order to celebrate abstract mathematical items that are somewhat irrational, the obvious solution is to incorporate pie into the holiday.

  3. Pi links mathematics to the real world

    Maybe when you were in math class, you stared off into space wondering why on earth ‘logs’ or ‘proofs’ mattered so much — pi is the answer. Well, at least it’s one of the things that links math back to real-world uses. Because pi is linked to circles it is also linked to cycles, things like calculating waves, ebb and flow, the ocean tides, electromagnetic waves, and much more. In addition, many natural world phenomena can also be calculated with pi — like the shape of rivers, the disc of the sun, the spiral of DNA, and even the pupil of an eye.

Pi Approximation Day dates

2024July 22Monday
2025July 22Tuesday
2026July 22Wednesday
2027July 22Thursday
2028July 22Saturday

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