They say the only constant in life is change. In mathematics, however, there are many constants, and today, we're celebrating perhaps the most famous of them all: pi. This tasty-sounding constant is the ratio of a circle's circumference to its diameter, approximately 3.14159. Every March 14, mathematics fans across the world get baking to mark Pi Day—a celebration of both the mathematical constant π and its delicious homophone, pie. It began in 1988, when physicist Larry Shaw connected the date (3/14) with the first three digits of this constant. Today, mathematicians and enthusiasts celebrate Pi Day with pie eating and pi reciting. Did you know that when your clock strikes 1:59 today, you will be three decimal places closer to the real value of pi? Pi is everywhere, even in nature. Pictured here is a bodhi tree in the shape of the pi symbol at Wat Phra Ngam, a temple in Ayutthaya, Thailand. Whether you're a math geek or just in it for the treats, Pi Day is for everyone to enjoy!