Today, March 14, 2018, is Pi Day - that's pi, not pie. Pi, denoted by the Greek letter “π”, has been part of human knowledge for millennia, but it wasn’t until 1988 that physicist Larry Shaw organized what is now recognized as the first “Pi Day” celebration at the San Francisco Exploratorium science museum. Shaw chose March 14, or 3.14 — the first three digits of pi — as Pi Day. As we celebrate again this year, here are some Pi facts for you!