What is pi? On National Pi Day 2017, millions will wonder about the millennia-spanning history that led to the facts about the irrational number’s value that we know today.

The simple answer, and the one recalled by anyone who got beyond remedial math in high school, is that pi is 3.14 and then some. Or, if you had a teacher that gave you extra credit for memorizing a few extra digits, 3.14159265359 and then some.

For those with a good enough memory to recall the concept beyond the numerical value, one might say it’s the ratio of the circumference of any circle to the diameter of that circle. In layman’s terms, it’s the distance around a circle divided by how wide it is across the middle, from any one point to the opposite side. No matter what circle, no matter what size, pi is essential to the formula that creates a perfect circle. Still confusing? *Scientific American* explains the facts of what pi is with this experiment.

“Using a compass, draw a circle. Take one piece of string and place it on top of the circle, exactly once around. Now straighten out the string; its length is called the circumference of the circle. Measure the circumference with a ruler. Next, measure the diameter of the circle, which is the length from any point on the circle straight through its center to another point on the opposite side. If you divide the circumference of the circle by the diameter, you will get approximately 3.14 — no matter what size circle you drew!”

Pi’s magic also shows up outside of geometry, though its appearance does always indicate that it somehow relates back to a circle or associated shapes like spheres, cylinders, cones, and ellipses. For instance, any time a wave or an oscillation of any kind is being measured, the concept of pi also holds true. Probability graphs, for example, also feature pi.

Those recalling none of these facts might simply think of drawing the symbol π, or rather a pie, or that trippy black-and-white Darren Aronofsky movie — any of which can be a great way to celebrate National Pi Day 2017. After all, according to some mathematicians, using March 3 (3/14) to celebrate pi doesn’t make a lot of sense anyway.

Daniel Ullman, a math professor at George Washington University, published an article in *The Conversation* two years ago arguing that the Gregorian calendar and the decimal system are “modern, human-made inventions, chosen arbitrarily among many equivalent choices” and because of that attaching National Pi Day to them does not respect its transcendental or ephemeral nature.

“In some sense that there isn’t ever going to be a simple way of describing π arithmetically. Nowadays, machines can compute trillions of decimal digits of π, but that in no way helps us understand what π is exactly. It’s easiest just to say that, to be exact, π is equal to … π… Perhaps in a century mankind will know the answer to this question, but it’s not even clear at this time how to attack it effectively.”

But, fear not, math haters. There’s also a lot of interesting history to delve into on National Pi Day for those of us who aren’t seduced by numbers. Use of pi has been around since at least the days of ancient Babylonians around 1900-1680 BCE, and some even argue that it was a foundation used in the construction of the pyramids in Egypt. John Taylor, the first person to present this idea in written form, argued that the pyramids were meant to be a physical representation of the sphere of the earth, folding over the sides of a circle to get a pyramid. Some, however, have argued that this was merely a coincidence, but efforts to understand pi begin to appear in Egyptian texts as far back as 1650 BCE.

Though the ancient Greeks may have known what pi was mathematically, they were actually not the first to associate it with π, the letter of the Greek alphabet that now stands in place for the value. The link between the two didn’t arise until 1706, when the son of a Welsh farmer, William Jones, published his book about the day’s most cutting-edge advances in facts about math *Synopsis palmariorum matheseos.* Over the next few decades, it slowly became the common way to describe pi, which is generally thought to be because it is closely related to the word “periphery.”

The long, arduous process that took thousands of years to reach around 500 digits of pi doubled to more than 1,000 with the invention of desk calculators in the 1940s, but these simplistic calculations were dwarfed by the invention of computing. By the ’70s, the number surpassed one million digits for the first time, and in 1989, it hit one billion for the first time.

Today, one can answer the question “What is pi?” to around 22 trillion, a precision that is attributable to a system designed by Shigeru Kondo and Alexander J. Yee, a Japanese systems engineer and an American computer science student, reported *The Mary Sue*.

National Pi Day 2017 will mark just the ninth year since the holiday was officially approved 391-10 by the U.S. House of Representatives in 2009. Part of an effort to focus attention on STEM studies, it received a high level of support despite an attempt to move away from commemorative bills in Congress. Rep. Brian Baird (D-Wash.) told *Politico* that he was honored to vote the observance into effect.

“I’m kind of geeked up about it… I have been fascinated by pi since I was a kid. It blows my mind. It’s lovely. The fact that it’s sort of this infinite number. I just think it’s this magical thing…. There’s a real beauty to mathematics.”

The tradition of National Pi Day to celebrate the history and significance of the irrational number also takes place in other countries, but they often ask “What is pi?” on the July 22 to coincide with the fraction that pi represents, 22/7, and the fact that many other nations around the world write their date with the day preceding the month.

[Featured Image by phloxii/Shutterstock]