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13 Fascinating Facts Behind the Mystery of Pi

Find out why this ancient mathematical constant gets an annual celebration—one that’s growing every year!

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1. People Have Been Using Pi for Thousands of Years

Pi (the Greek letter π, pronounced like the word “pie”) is the ratio of the circumference of any circle to the diameter of that circle, explains math instructor Steven Bogart in Scientific American. It equals roughly 3.14. No matter what size a circle is, the circumference will always be 3.14 times bigger than the diameter.

Over 4,000 years ago, the ancient Egyptians and Babylonians had figured out this constant and were using it to make calculations. In the 18th century, mathematicians gave the number the name “pi.”

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2. We Celebrate Pi on March 14

Back in 1988, Larry Shaw of San Francisco’s Exploratorium science museum started observing March 14—get it? 3/14!—which also happens to be Albert Einstein‘s birthday, as Pi Day. By 2009, the celebration had grown so big that the United States Congress passed a resolution to make the designation official. The resolution states: “The House of Representatives supports the designation of a ‘Pi Day’ and its celebration around the world … and encourages schools and educators to observe the day with appropriate activities that teach students about Pi and engage them about the study of mathematics.” In another stamp of approval, in 2010, Pi Day got its own Google Doodle.

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3. Pi is a Never-Ending Number

Pi is an irrational number. It can’t be expressed as a fraction; it doesn’t end with a repeating pattern (like the decimal expression of 1/3, 0.33333…, in which the threes repeat forever), or terminate after a certain number of decimal places (like 3/4, or .75). It just keeps going, going, and going. So far, pi has been calculated to over 22 trillion digits. It took a computer with 24 hard drives, working nonstop for 105 days, to make that calculation.

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4. More Pi Isn’t Necessarily Better

While we know pi to more than a trillion places, we really don’t need them. Scientists can determine the spherical volume of the entire universe using just 39 places past the decimal, according to piday.org. NASA’s Jet Propulsion Laboratory only uses pi up to 15 decimal places for its robotic space and earth science missions. “For JPL’s highest accuracy calculations, which are for interplanetary navigation, we use 3.141592653589793,” explains engineer Marc Rayman. “There are no physically realistic calculations scientists ever perform” that would require more decimal points than that.

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5. The Digits of Pi After the Decimal Point Are Random

The trillions of digits of pi that have been calculated continue without any discernible pattern. Mathematicians have been looking for those patterns for centuries, but as far back as 1768, a self-taught Swiss-German mathematician and astronomer named Johann Lambert proved that pi is irrational.

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6. American Lawmakers Once Tried to Round Up Pi to 3.2

If we don’t need all those decimal places in pi, wouldn’t it be easier to just call it 3.2? In 1897, an Indiana doctor decided that the world should go ahead and use 3.2 for any calculations requiring pi. Dr. Edwin Goodwin proposed a bill in the state legislature. He even copyrighted this idea and planned to charge royalty fees for anyone who used it—except for those in the state of Indiana. After some debate, the state senate realized that the idea of using a law to change a mathematical constant was a silly one, and the law failed to pass.

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7. Someone Has Memorized 70,000 Decimal Places of Pi

The Guinness Book of World Records recognizes Rajveer Meena as the champion memorizer of digits of pi. On March 21, 2015, at VIT University in Vellore, India, Meena recited pi to 70,000 places past the decimal point. A 21-year-old student at the time, Meena proved his powers of memory by reeling off the numbers while wearing a blindfold. It took him more than nine hours to do it.

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8. You Can Borrow Expert Memorizers’ Techniques

How in the world does someone memorize a string of 70,000 random numbers? Most record holders (or just interested hobbyists) use an association technique. They bunch smaller groups of numbers together and memorize those: 14, then 15, then 92, then 65, and so on. Or they may look at each set of nine digits as a telephone number and memorize them that way. Another strategy is to match each digit or small groups to a word, then make a story out of those words. Yet another method is spatial visualization, in which you picture a familiar place, then assign numbers to different spots in that place. To recall them, you mentally walk through the space and see the numbers as you go.

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9. Pi is a Record Setter in More Ways Than One

Aside from Rajveer Meena’s achievement, other Guinness World Records have been awarded to pi-themed accomplishments. In 2014, 589 people at a grammar school in Germany formed the largest human pi symbol. And in 2017, 520 teachers and students in Todi, Italy, formed the longest human representation of pi digits. The city’s mayor held up a sign bearing the number 3, and then each person after him stood in for a digit of pi after the decimal place.

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10. Pi Has Many Real-World Uses

It’s not all fun and games and feats of memory: Scientists use pi every day to make important calculations, such as determining the volume of a sphere, the area of a circle, and the volume of a cylinder. “Those relationships form the basis for how stiff a structure is, how it will vibrate, and understanding how a design might fail,” says Charles Dandino, an engineer at the Jet Propulsion Lab. “In my career, pi has allowed me to calculate the size of a shield needed to enter the atmosphere of Venus and the size of a parachute that could safely land the Curiosity rover on the surface of Mars,” says another JPL engineer, Anita Sengupta.

Another handy tool that makes use of pi? The GPS system in your car and smart phone use it to calculate specific locations on Earth.

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11. Do a Magic Trick to Calculate Pi

To try this easy activity known as Buffon’s Needles, you need a large sheet of paper, at least 30 toothpicks, a ruler, and a pen. Using a toothpick to determine the distance between them, draw a series of parallel lines on your paper. Then throw the toothpicks onto the paper at random.

Next, take away any toothpicks that are only partially on the paper, or that didn’t land on the paper at all. Count how many are left on the paper. Also, count how many cross a line.

Divide the total number of toothpicks by the line-crossing toothpicks. Now multiply by two, and you should get pi!

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12. Pi Can Go the Distance

You can see what pi to one million decimal places looks like, here, at piday.org (keep scrolling!). Another way to visualize this super-long number? If you printed out pi to a billion decimal values, in 12-point font, you’d need a piece of paper that stretched halfway across the USA, from Kansas to New York City.

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13. Pi Inspires Poetry

You can also observe Pi Day with a poem…or a “piem!” Pilish unites math enthusiasts and word nerds. To compose in it, you must use words in which the number of letters corresponds, in order, to the numbers in pi’s sequence. So since pi = 3.14159, your poem must start with a three-letter word, then a one-letter word, then a four-letter word, another single letter, and so on: “‘Aha,’ I said, ‘a fancy alligator … ‘”

Hate crossing the border? Try being a poet!

Originally Published on Reader's Digest