A holiday associated with a math constant may not seem very exciting. But Pi ("π") Day, observed annually in the US on March 14 (3/14), is an exception. That's because the celebrations may start with math activities centered around pi — the ratio of the circumference of a circle to its diameter, widely recognized as 3.14. But they inevitably end with a slice or two of delicious pie!

The first Pi Day celebration was organized by Larry Shaw, a technical curator at San Francisco's Exploratorium Museum. On March 14, 1988, he asked colleagues to join him in a parade around the museum's "pi shrine" — a metal disk engraved with the first 100 digits of pi — and eat fruit pies. The group had such a good time that museum officials turned Pi Day into an annual celebration. Visitors participated in special pi-related activities and ate free, sample-sized savory pies. As news of the fun event spread, schools, libraries, and universities around the US also began to observe Pi Day. In 2009, the US Congress designated March 14 as National Pi Day.

Today, Pi Day is celebrated in many creative ways. Every March 14 and March 15, female television meteorologists around the country dress in purple. The movement, known as "Dress for STEM," began seven years ago after an image of hundreds of forecasters wearing the same dress, albeit in different colors, went viral. The weather scientists decided to repeat the fun coincidence annually to encourage more girls to consider careers in science, technology, engineering, and math.

March 14, which also happens to be Albert Einstein's birthday, holds a special significance for Princeton, New Jersey. This is where the renowned scientist spent the last two decades of his life. The city celebrates the two special occasions with an "irrational" number of events, which include pie-eating, pi-recitation, and Einstein look-alike contests.

Many retailers also get into the holiday spirit with special deals on pies, pizzas, and other goodies. This year, Blaze Pizza, 7-Eleven, and Round Table Pizza will sell select pizzas for just $3.14 on March 14. Those looking for the sweeter varieties will be able to get a free slice of pie from Coco's Bakery.

Though Pi Day celebrations are relatively new, the numerical constant has been known to humanity for thousands of years. The Babylonians, who used it 4,000 years ago to determine the area of a circle, gave pi a value of 3. The ancient Egyptians came closer to the real number in 1650 BC, when they approximated pi to be 3.165. Archimedes of Syracuse (287-212 BC), the first to calculate the constant mathematically, gave pi a range of between 3 1/7 and 3 10/71. Given that all the numbers were derived without calculators or computers, their proximity to pi's actual value — 3.14 — is truly impressive!

Resources: wikipidea.org, exploratorium.edu, retailmenot.com, visitprinceton,org