Pi is an irrational number, meaning it has an infinite number of nonrepeating decimal places. But it turns out, NASA scientists need only a small slice of pi — the first 15 decimal places — to solve most of their math problems. And even when working out problems on the most mind-bending cosmic scales, they never need more than a few dozen extra digits.
You may remember pi from school. It's the ratio between a circle's diameter (the distance between opposite points) and circumference (the distance around the edge). Simply put, pi is equal to the circumference of a circle divided by its diameter, which means you can figure out the circumference of any circle if you know its diameter or radius (half the diameter) and pi, which is most commonly abbreviated as 3.14 — which is why Pi Day is celebrated on March 14.
