In order to celebrate Pi Day, we TED-Ed nerds are bringing you 3 fun facts about our favorite irrational number!

1. Pi is infinite! To write it out, you’d begin with 3.14159 and continue on….forever! That’s why, instead of trying to write out an infinite number of digits every time, we just refer to it using the Greek letter, Pi.

2. Pi is an irrational number, or a number that can never be expressed as a ratio of 2 whole numbers.

3. Scientists have used Pi to calculate the density of our entire universe, which has infinitely less stuff in it than the total number of digits in Pi.