Pi Day is an unofficial observance commemorating the mathematical constant π (pi), which is the ratio of a circle’s circumference to its diameter (3.14159…). The date is derived from the first three digits of pi (3.14) using American dating order. (Coincidentally, it is also Albert Einstein’s birthday.)

Many celebrate Pi Day by performing pi-related activities; some serious and some less so — such as creating pi puns, baking, throwing and eating pies, and singing pi songs. 2015 is going to be a big year for pi since we will celebrate 3.14 15 (correct to 4 decimal places).

**The Importance of Pi**

Pi has been crucial to the development of modern life. As far back as the ancient civilizations of Babylon and Egypt, people needed approximations of pi to deal with the flooding of the Tigris, Euphrates and Nile rivers, for astronomy, and for surveying and building ziggurats and pyramids. The ancient Greeks were the first to study pi for its own mathematical sake.

Pi appears most often in formulas involving circles or periodic motion, and it infiltrates some fundamental physical constants. These constants appear all over physics: masses of elementary particles, the number of molecules in a volume of a gas, the forces holding matter together, and so on.

**International Pi Day**

The first time a day was dedicated to pi was on March 14, 1989 at the Exploratorium, a museum of science, art and human perception in San Francisco. The idea was the brainchild of Larry Shaw, a physicist at the center.

Many North American and UK schools use International Pi Day to spark interest in math and science projects (e.g., learning how the Greeks or Arabs did arithmetic; studying famous scientists like Gauss, Newton or Archimedes who worked on pi; or perhaps calculating the volumes of real pies before eating them).

In 2009, the U.S. House of Representatives formally declared March 14 National Pi Day, in House Resolution number 224. The resolution urged schools and educators to teach children about the importance of pi in human history and generally engage students in the study of mathematics.

Find out more at www.piday.org.

Source: Jonathen M. Borwein, “Pi Day in America,” Huffington Post, March 14, 2012, accessed March 8, 2013, http://www.huffingtonpost.com/jonathan-m-borwein/pi-day_b_1341569.html.