What's Pi Day all about? Math, science, pies and more

Math enthusiasts around the world, from college kids to rocket scientists, celebrate Pi Day on Thursday, which is March 14 or 3/14 — the first three digits of an infinite number with many practical uses.

Around the world many people will mark the day with a slice of pie — sweet, savoury or even pizza.

Simply put, Pi is a mathematical constant that expresses the ratio of a circle's circumference to its diameter. It is part of many formulas used in physics, astronomy, engineering and other fields, dating back thousands of years to ancient Egypt, Babylon and China.

Pi Day itself dates to 1988, when physicist Larry Shaw began celebrations at the Exploratorium science museum in San Francisco. The holiday didn’t really gain national recognition though until two decades later. In 2009, Congress designated every March 14 to be the big day — to hopefully spur more interest in math and science. Fittingly enough, the day is also Albert Einstein's birthday.

Here's a little more about the holiday's origin and how it's celebrated today:

Pi can calculate the circumference of a circle by measuring the diameter — the distance straight across the circle's middle — and multiplying that by the 3.14-plus number.

It is considered a constant number and it is also infinite, meaning it is mathematically irrational. Long before computers, historic scientists such as Isaac Newton spent many hours calculating decimal places by hand. Today, using sophisticated computers, researchers have come up with trillions of digits for pi, but there is no end.

It wasn't given its name until 1706, when Welsh mathematician William Jones began using the Greek symbol for the number.

Why that letter? It's the first Greek letter in the words “periphery” and “perimeter,” and pi is the ratio of a circle's periphery — or circumference — to its diameter.

The number is key to accurately pointing an antenna toward a satellite. It helps figure out everything from the size of a massive cylinder needed in refinery equipment to the size of paper rolls used in printers.

Pi is also useful in determining the necessary scale of a tank that serves heating and air conditioning systems in buildings of various sizes.

NASA uses pi on a daily basis. It's key to calculating orbits, the positions of planets and other celestial bodies, elements of rocket propulsion, spacecraft communication and even the correct deployment of parachutes when a vehicle splashes down on Earth or lands on Mars.

Using just nine digits of pi, scientists say it can calculate the Earth's circumference so accurately it only errs by about a quarter of an inch (0.6 centimeters) for every 25,000 miles (about 40,000 kilometers).

“One of the basic rules of the universe is that nothing is perfect. Perfection simply doesn’t exist. Without imperfection, neither you nor I would exist.”