Thursday is Pi Day, the day of the year that matches the number pi in its shortest version: 3.14.
Mathematicians know 3.14 are the first three numbers in pi - the ratio of the circumference of a circle.
This is the 24th year Pi Day is being celebrated. It began at the San Francisco Exploratorium in 1989. Staff and visitors at the science museum walked around one of the circular spaces. They then concluded the celebration by eating slices of fruit pies.
Since then, the Pi Day celebration has gone worldwide. In 2009, the U.S. House of Representatives passed a resolution officially declaring March 14 as National Pi Day.