Larry Shaw was a technical curator at the San Francisco Exploratorium. During a staff retreat in 1988, he came up with the idea of linking March 14 (3/14) with the digits of the most famous mathematical constant, pi (π = 3.14159…).

Seeing it as an opportunity to bring the staff together, the Exploratorium celebrated the first Pi Day on March 14 at 1.59 pm with a table full of fruit pies, a tea urn, and a parade. The idea gradually spread out and now has become a celebratory day for mathematics enthusiasts all over the world.

In 2019, UNESCO proclaimed the day to be the International Day of Mathematics. March 14 also marks the birth anniversary of Albert Einstein and the death anniversary of Stephen Hawking. Coincidence much?

**Introduction to Pi**

You must have encountered pi for the first time in middle school, probably when you were learning to find the area of a circle. But, what is pi? Ask a linguist, they would say it is a Greek letter. An engineer would say, it is a constant and values 22/7 (or worse, 3). A physicist would probably say it is 3.14. A mathematician, who has a better way with definitions and theorems, would first offer an experiment.

Find two to five circular-shaped objects in your house - coins, bottle caps, CDs, or even car wheels. Use a thread to measure their circumference. Approximately measure their diameter too. Put these data into a table and write the ratio of circumference to diameter for each of these objects.

Depending on the accuracy of your measurements, you will probably get a value just above 3 for all of them, irrespective of the size of the object. That is what pi is - the ratio of a circle's perimeter to its diameter.

It is irrational (cannot be written in a fractional form), transcendental (not the root of a non-zero polynomial of finite degree with rational coefficients), and an infinite decimal (after the decimal point, the digits go on forever and ever).

**Historically speaking**

The history of pi goes back to 4,000 years and it is a story that weaves across various civilisations. The constant was known by both the Egyptians and Babylonians. But, the first recorded calculation of pi was done by Archimedes of Syracuse in the 3rd century BCE.

But, it wasn't until the 18th century that the constant started being denoted by the Greek letter π, thanks to the Welsh mathematician William Jones. As of 2021, computer algorithms have helped us approximate pi to around 62 trillion decimal places.

Apart from the familiar use of pi in mathematics, it also plays an important role in astronomical calculations, planetary studies, getting spacecraft into orbit, industrial engineering, and signal processing.

Pi is also a good random number generator and finds its application in cryptography. All these may sound advanced. But, you can have a fun application of pi in your daily life too.

Ever calculated how many litres of coffee you drink every day? Pi can help you find it. Pick up your coffee mug (assuming it is the usual cylindrical-shaped mug), measure its diameter and height (h), both in centimetres.

Divide the diameter by 2, you get its radius (r). Now, use the formula “pi*r*r*h”, and multiply that value with the number of cups you drink every day. Divide that by 1,000 and voila, you get your coffee volume measured in litres! You can use similar formulae to find the volume of your container, bottle, cereal bowl, and even water tanks.

Larry, the man behind Pi Day, believed that the basic tenet of the celebration is to make maths seemingly accessible to people who have had a not-so-good experience with it in their school days.

Schools have a way of instilling the fear of maths in kids. I am glad that my middle school math teacher introduced pi to me as the ratio of circumference to diameter of a circle and not as a random constant with no personality.

I still vividly remember doing the circumference/diameter exercise that I mentioned earlier, sitting by candlelight (not because candles were my homework aesthetic, but because it was a power cut night).

But, mathematics, in reality, is more than computations and memorisation of formulas. It works with the basic principle of the human mind - seeking patterns, pushing its limits with existing knowledge, and arriving at new conclusions, and more often leans towards philosophy than science. Hope this Pi Day helps your inner child to reconnect with mathematics.

*(The author is a postgraduate in maths with a penchant for history and the written word)*