Thursday is Pi Day, a national celebration of the mathematical concept, which is the ratio of a circle's circumference to its diameter and equals 3.14... Four years ago, 3-14-15, was the only day this century that matched pi, commonly approximated as 3.14159.

Schools and museums often plan events to celebrate the concept, which has fascinated humans for centuries. And, some people celebrate by eating a piece of pie or an entire pizza.

In the spirit of the holiday, here are 3.14 things you may not know about pi:

### U.S. & World

**1. No one is certain who discovered pi as we know it today**

But we do have some ideas. It seems that the Egyptians used pi in the construction of the Great Pyramid because when the perimeter is divided by its height, one gets a close approximation to 2π. It’s the same result if one divides the circumference of a circle by its radius.

But the most significant pi research might have come from the astronomer, Archimedes, around 250 B.C.

His mathematical calculation showed that pi was "between three and one seventh and three and 10 seventy firsts,” Steven Strogatz, an applied mathematics professor at Cornell University, told NBC in a 2015 interview. “He approached that putting a six-sided figure into a circle, then made it 12 sided, and went all the way up to a 96-sided polygon.”

He proved that pi was found somewhere between these two numbers, which applied to all circles.

**2. You can find your identity in pi**

One myth is that since pi is a continuation of numbers, people’s identities can be found in the pattern: like social security numbers or birthdays.

This theory, which had circulated around Reddit for years before getting a popularity jolt from a George Takei Facebook post (that post appears to have been taken down), posits that all number combinations can be found within the digits of pi.

A version of this theory posted on Reddit says of pi: "Converted into a bitmap, somewhere in that infinite string of digits is a pixel-perfect representation of the first thing you saw on this earth, the last thing you will see before your life leaves you, and all the moments, momentous and mundane, that will occur between those two points."

But Professor Strogatz stressed that the meme is misleading. Even if it is true (which is not yet known), the digits in pi would tell us nothing about a person's life or identity, because along with correct social security numbers and birthdays, there will also be wrong social security numbers and birthdays.

**3. Proving pi with matches**

You can prove pi exists with matches, toothpicks, a pen, or anything else that is the same length, explained Johnny Ball, the author of “Why Pi? (Big Questions).”

“There’s a wonderful way to find pi for yourself. You find a floor with parallel lines; you find matches, pins, pens, exactly the same length. If you drop a hundred of them at random on the floor, the points touching a line will equal pi,” Ball said.

The matches' length must be equal to the distance of the two parallel lines. After the matches are dropped, you multiply the number of matches thrown down by two and divide it by the total number of matches that touched a line, which will equal pi.

This problem was discovered in the 18th century by French mathematician Georges-Louis Leclerc, Comte de Buffon.

Check out this video on Dr. Tony Padilla's YouTube channel Numberphile where he demonstrates Buffon's Needle Problem:

**3.14...Legislating against pi**

In 1897, Indiana state legislators tried passing a Pi Bill that legally defined pi as 3.2. Edward J. Goodwin, a physician, convinced a well-known mathematical monthly newspaper that he had solved what mathematicians had tried to do for generations: squaring the circle. Simply put, squaring the circle is the impossible task of finding the area of a circle by finding the area of a square around it. Goodwin claimed that pi was 3.2 instead of a continuous number. The bill never became a law thanks to Professor C. A. Waldo who convinced the Indiana Senate that Goodwin’s discovery was not possible.