Every year, March 14th is Pi Day in honor of the irrational number, which cannot be expressed as a fraction. 28 years ago, physicist Larry Shaw began honoring the holiday at San Francisco’s Exploratorium, where he began to celebrate with fellow staffers as well. Although it was used before, the Greek letter pi wasn’t always associated with the number, until the 1700s. Now, the holiday is used as an excuse to eat pie. So to all those math and pie enthusiasts out there, HAPPY PI DAY!