Happy Pi Day, everyone!

No…not THAT kind of pie! We’re talking about pi, or **π.**

**Pi is a number**: 3.14 to be exact. Well, 3.1415926535897932384626433832795028841971693993751058209749

445923078164062862089986280348253421170679821480865132823066

470938446095505822317253594081284811174502841027019385 to be MORE exact. We could try to be even MORE precise, but…pi literally goes on forever!

National Pi Day was established in 2009 to promote mathematics and all sorts of delicious edible pies as well

**So, what is π?**

Pi represents the ratio of a circle’s circumference to its diameter. You can refer to this ratio as pi or the Greek letter π. The circumference is the distance around the circle and the diameter is distance measured by a straight line passing from one end to the other through the center of the circle. To calculate the circumference of a circle, multiply its diameter times pi. Therefore, by definition, if the diameter of a given circle is 1, then its circumference will be pi.

Why is **π so special?**

Pi is special because it is an **irrational number.** That means that it can’t be expressed as a simple fraction (one number divided by another). 22/7 comes close to pi, but it’s not accurate. Another reason pi is special is because it is a **transcendental number.**

Other famously irrational numbers include Euler’s number and φ (the Greek letter “phi”, known as “the Golden Ratio”). Euler’s number is also transcendental, but φ is not.

Pi continues to fascinate people because even after hundreds of years of studying it, we cannot determine whether there’s a pattern to its digits, or if they are truly random. They are likely random, and if that is the case, the digits of pi contain every pattern in existence and will never repeat. There’s something beautiful in the idea that circles are perfectly round and enclosed, but what’s needed to define them (pi) is infinite and random.

If you haven’t had your fill of pi, Danica Keller explains more in an episode of “Math Bites” below.