Pi Day is celebrated annually on March 14 (Credit: Dennis Wilkinson/ CC-BY-SA-2.O/ Flickr)

A holiday celebrating 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. The celebrations usually 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 typically end with a slice or two of delicious pie!

Pi Day was first celebrated at San Francisco's Exploratorium Museum. On March 14, 1988, employees paraded around the museum's "pi shrine" — a metal disk engraved with the first 100 digits of pi — and ate fruit pies. They had such a good time that museum officials turned Pi Day into an annual celebration. Visitors participated in special pi-related activities and enjoyed slices of pie. 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.

The holiday is now celebrated in many creative ways. Every March 14 and 15, female television meteorologists report the weather dressed in purple. The movement, known as "Dress for STEM," began in 2015. It is meant to encourage more girls to consider careers in science, technology, engineering, and math.

Applicants to the Massachusetts Institute of Technology (MIT) eagerly await Pi Day. That's when they discover if they have been accepted to the prestigious university. But instead of sending out the notifications at 3:14 PM EST, MIT waits till 6:28 PM EST. The number, which equals 2π, is called Tau. Some experts believe it is easier to use than pi.

Princeton, NJ, celebrates Albert Einstein's birthday on Pi Day (Credit: Visitprinceton.org)

Pi Day also happens to be Albert Einstein's birthday. Princeton, New Jersey, where Einstein lived from 1935 until he died in 1955, marks the occasion with a multi-day festival. It includes fun activities like pie-eating, pi-recitation, and Einstein look-alike contests.

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

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