Today, March 14, is a special day for those who are into mathematics or science. It’s “Pi Day” or “Π Day”, the annual worldwide celebration of the ancient mathematical constant. It’s also the birthday of Albert Einstein who was born on March 14, 1879.

Pi Day has been commemorated in one way or another since physicist Larry Shaw organized the first celebration back on March 14, 1988, while working at a San Francisco museum called the Exploratorium.

Pi, a letter in the Greek alphabet, stands for the ratio of a circle’s circumference to its diameter. Rounded out, it is equal to approximately 3.14.

Historians have tracked the use of a constant ratio in making mathematical calculations as far back as the ancient Babylonians and Egyptians about 4,000 years ago.

In calculating the area of a circle, the ancient Babylonians used a formula that took three times the square of its radius. Some of these calculations set pi to equal 3 and while others have it as 3.125.

According to an ancient Egyptian papyrus, the builders of the Great Pyramids calculated the area of a circle with a formula that set the estimated value of pi as 3.1605.

It wasn’t until the ancient Greek mathematician Archimedes approximated the area of a circle by using the Pythagorean Theorem that pi was first calculated. He determined pi was equal to a number between 3 1/7 (3.14285714) and 3 10/71 (3.14084507).

Historians have also pointed to calculations made by Zu Chongzhi, a brilliant Chinese mathematician and astronomer who lived about 200 to 300 years before Archimedes. Not much is known about Zu Chongzhi, books of his works have been lost, but he was said to have calculated the value of the ratio of the circumference of a circle to a diameter as 355/113 or approximately 3.14159292.

The use of the Greek letter π to signify the ratio of the circumference of a circle to its diameter was introduced in 1706, by Welsh mathematician William Jones, a close friend of Sir Isaac Newton.

Part of pi’s charm and mystique comes from the fact that it’s a number that can never be fully calculated to an exact value, because it goes on and on indefinitely without repeating or establishing any kind of regular pattern.

Over the centuries, mathematicians, scientists and others have enjoyed the challenge of trying to calculate π to as far of a decimal point as possible.

The current world’s record for calculating pi was set on December 28, 2013, by math enthusiasts and computer scientists Alexander J. Yee of the US and Shigeru Kondo of Japan. The two, using a computer they built, calculated pi to 12.1 trillion digits past the decimal point.

March 14 is an extra-special day in Princeton, New Jersey. Not only is it Pi Day, but they also celebrate the birth of a famous former resident, physicist and creator of the theories of relativity, Albert Einstein who lived and worked there for over 21 years.

In 1933, as Adolf Hitler and the Nazis were rising to power in Germany, Einstein, who was Jewish, fled his homeland and settled in Princeton to work at the Institute for Advanced Study.

This year, Pi Day/Albert Einstein’s Birthday in Princeton is a 3-day celebration featuring a Pizza Pi “Top Chef” competition, an Albert Einstein lookalike contest and a Rubik’s Cube demonstration.

So whether it’s a gathering of friends enjoying a Pi Pie, participating in pie-throwing contests, or taking part in competitions to calculate pi to the largest decimal place, have fun! After all, Pi Day only comes once a year.