The Most Interesting Facts About the Magical Number Pi

Not every mathematical constant gets its own day. But not every constant is π.

Pi Day got started in 1988 in San Francisco, when Larry Shaw, the legendary technical curator of the city's Exploratorium, saw the connection between March 14 (3.14) and pi (3.14159…). Add in the fact that 3/14 is Albert Einstein's birthday and you've got a ready-made celebration.

Pi seems simple: It's the ratio of a circle's circumference to its diameter. Under the surface, though, it's anything but. Mathematicians have spent centuries finding more and more digits of pi and discovering ways in which it intersects with the rest of mathematics.