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31 Gotta-Know Fun Facts About Pi Day

Pi Day is celebrated every year on March 14, since the first three significant digits are 3, 1, and 4. But what is Pi? When do we use it? And why? The mysteries of this mathematical symbol used to represent the ratio of the circumference of a circle to its diameter (3.14159) are infinite. We’ve collected 31 fun facts to get your students thinking—and excited to come up with more facts of their own!

1. Because π repeats infinitely in an unpredictable sequence, we can never truly measure the area (πr2) or circumference (2πr) of a circle.

2. It’s common to use Greek symbols as variables in mathematics. π, pronounced “Piwas” in Greek, is the 16th letter of the Greek alphabet, while P is the 16th letter of the English alphabet.

3. The number π holds true to its Greek roots. It’s the first letter of the Greek words “perimeter” and “periphery”, which are both synonymous with circumference. In English π is the ratio of a circle’s diameter to its circumference.

4. The symbol π wasn’t always used to represent the constant circle ratio. It wasn’t until 1706 that William Jones (1675-1749) started using the symbol, which was later popularized by Leonhard Euler (1707-1783) in 1737.

5. Because π is connected to circles in so many ways, scientists were interested to find that 360, the number of degrees in a circle, is the 359th-361st digits of π.

6. Ludolph van Ceulen (1540-1610) spent decades calculating the first thirty-six digits of π, which are now named the Ludolph number. It is thought that this number is engraved on his now lost tombstone.

7. Ceulen’s discovery was impressive, but a couple centuries later William Shanks (1812-1882) discovered what he thought were the first 707 digits of π. It turns out he was mistaking after the first 527 digits, but it was still a critical discovery in the math community.

8. Around 150 years later in 2002, a Japanese scientist decided to give calculating π a try using the super computer, Hitachi SR 8000. While Ceulen and Shanks were both limited to calculating their digits by hand, using Hitachi, the first 1.24 trillion decimal places of π were able to be calculated.

9. If one were to use π rounded to the 9th decimal place to measure the circumference of the earth, there would only be an error of less than a quarter of an inch every 25,000  miles.

10. The first 39 decimal places of π are sufficient for determining the circumference of the entire universe with a margin of error equal to less than the radius of a hydrogen atom.

11. Now you may be asking yourself why we need 1.24 trillion decimal places if 39 is enough to calculate the circumference of virtually any circle? Well, the truth is that humans don’t, however, calculating π is the perfect test for determining the strength of super computers.

12. Humans have been studying π for almost 4,000 years. In around 2,000 B.C.E. the ancient Babylonians determined that the constant circle ratio (π) was 3.125. This was the first known value for π.

13. One of the first recorded instances of π was from an ancient Egyptian named Ahmes in 1,650 B.C.E. He wrote it on a Rhind Papyrus as 3.143, which is less than 1% off of the current approximation of 3.141592. This was also the first attempt to measure Pi by building a square inside a circle (squaring a circle).

14. The Great Pyramid at Giza (2,500 B.C.E.) is thought to have been constructed based on π. The relationship between the height and perimeter of the pyramid is the same as the relationship between the radius of a circle and its circumference.

15. Even the bible references π in Kings 7:23. It describes the altar in Solomon’s temple as “a molten sea of ten cubits from brim to brim” with a line of 30 cubits “compassing it round about”. This makes the equation for the dimensions of the alter 333/106, which equals 3.141509. Sound familiar?

16. In 800 A.D., Baghdad scientist Al-Khwarizmi calculated π out to four digits (3.1416). This was the first time the Baghdad community had access to this information, and the reason why the word “algorithm” is derived from Al-Khwarizimi’s name.

17. Traditionally, the circle represents the world of the sPiritual, infinite, and unknown, while the square represents the measurable and comprehensive world. Given these long-standing views, it’s interesting that in order to solve the mystery of measuring a circle one has to square it.

18. The Chinese were able to obtain an accurate representation of π long before the west. This is because European mathematicians didn’t use a symbol for zero until the late middle ages, after they adopted it from Indian and Arabic thinkers. Not only that, but the Chinese used decimal notations far before the west, making it possible for them to write out π ‘s many decimal points.

19. Initially some mathematicians calculated π by inscribing polygons with more and more sides. The more sides the polygon had, the closer it would approach to the area of a circle. Archimedes managed to inscribe a 96-sided polygon, and Chinese Mathematician Liu Hui used  a 3,072-sided polygon to calculate π to 3.14159. However, perhaps the most impressive feat using this method is that of another Chinese mathematician, Tsu Ch’ung, and his son, who together managed to inscribe a 24,576-sided polygon, which successfully calculated π with only an 8-millionth of 1% difference from the current accepted value.

20. Understanding π is useful in all sorts of disciplines. From number theory to probability to even chaos theory, π is an essential constant in the math world.

21. It wasn’t only scientists who were fascinated by π. Artists Leonardo da Vinci (1452-1519) and Albrecht Durer (1471-1528) both played around with the idea of squaring the circle to approximate π. This can be clearly seen in da Vinci’s Vitruvian Man drawing.

22. Many mathematicians would argue that circles actually have an infinite number of corners, rather than being perfectly cornerless.

Pi Pie
The circular circumference of Pie clearly illustrate the infinite nature of Pi.

23. You can use the fraction 355/113 to approximate π with an error of less than one-billionth of a percent. Alternatively, if you’re worried about simplicity over accuracy, you can use the fraction 22/7 to approximate π with an error of less than one-tenth of a percent.

24. At decimal place 763 there are six nines in a row, earning this spot the name Feynman’s Point.

25.  People have often mused about if the infinite digits of π  contain some kind of hidden message. For instance, in Carl Sagan’s book “Contact”, the digits of π contain a communication from aliens.

26. If you were to print out 1 billion decimal places of π it would stretch nearly 1,500 miles.

27. Ever wondered what the first 750 digits of π look like when written out?

28. You can find important dates and numbers in terms of π using this Pi-search page.

29. The world record for the most decimal places of π recited by memory is held by Chao Lu of China, who can recite π up to 67,890 places.

30. Albert Einstein, Ansel Elgort (a Fault in Our Stars), and Michael Caine (Alfred in “Batman”) were all born on Pi Day, so get out there and celebrate for these guys!

31. What do you get if you divide the circumference of a jack-lantern by its diameter? Pumpkin Pi!

Pumkin Pi Pie