What is Pi Day and who discovered the magic number?

Enjoy a slice of pi.

Math enthusiasts around the world, from school kids to rocket scientists, are celebrating Pi Day today, March 14 – or 3/14, also 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 – savoury in the UK, but possibly sweet or even a slice of pizza in the US.

Put as simply as possible, pi is a number used to calculate a circle’s circumference. 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.

What is pi?

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, but 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.

Why is it call pi?

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.

What is pi used for?

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 0.6cm for every 25,000 miles.

It’s not just maths!

Every year the San Francisco museum that coined the holiday organises events, including a parade around a circular plaque, called the Pi Shrine, 3.14 times – and then, of course, festivities with lots of pie.

Around the US, many events now take place on college campuses. For example, Nova Southeastern University in Florida will hold a series of activities, including a game called ‘Mental Math Bingo’ and event with free pizza (pies) – and for dessert, the requisite pie.

‘Every year Pi Day provides us with a way to celebrate math, have some fun and recognize how important math is in all our lives,’ said Jason Gershman, chair of NSU’s math department.

Nasa has its annual ‘Pi Day Challenge’ online, offering people plenty of games and puzzles, some of them directly from the space agency’s own playbook such as calculating the orbit of an asteroid or the distance a moon rover would need to travel each day to survey a certain lunar area.

The holiday hasn’t quite taken off to the same extent in the UK, but there are still plenty of events across the country, including Coventry Cathedral’s entire Pi Week and major celebrations at the University of Westminster, including the results of its Great Pi Challenge.

What about Einstein?

Possibly the world’s best-known scientist, Albert Einstein was born on March 14, 1879, in Germany. The infinite number of pi was used in many of his breakthrough theories and now Pi Day gives the world another reason to celebrate his achievements.

In a bit of math symmetry, famed physicist Stephen Hawking died on March 14, 2018, at age 76.

Still, pi is not a perfect number. He once had this to say: ‘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.’