People celebrate Pi Day every year on March 14 because the date matches the first three numbers of pi, 3.14. Pi is a number that shows the relationship between the distance around a circle and the width across its center. It is about 3.14159, and its numbers continue forever. Many students use pi at school to calculate the area of a circle or the volume of a cylinder.

Pi Day began in 1988 at the Exploratorium, a science museum in San Francisco, by a physicist named Larry Shaw. The event grew from a small staff party with pi into a popular public celebration.

Pi is also used in many areas of modern science. Artur Davoyan, a professor at the University of California, Los Angeles (UCLA), said that pi is used in almost every formula in mechanical and aerospace engineering. He also added that it helps scientists study the movement of spacecraft, different materials, and radio waves. Pi is also important when NASA sends signals to Voyager 1 and Voyager 2 and receives the signals that come back.

Dino Di Carlo, also at UCLA, said that pi is used in research on very small drops of liquid. His work may help scientists study cells and find antibodies that could block signals from cancer cells.