# Once A Century World Pi Day

By Maths Doctor Friday, March 13, 2015

Pi day occurs every year on March 14, however this year is a particularly special year. Any thoughts as to why?

This year the date becomes 03.14.15 (incidentally this is also Albert Einstein's Birthday) and therefore coincides with the first five digits of pi (3.1415).

## What is Pi?

Pi is a fundamental component to the fields of mathematics and physics, therefore rightly has its own day where it can be celebrated by maths lovers around the world.

So what is pi exactly? Pi () is defined as the ratio of a circle’s circumference to its diameter where Pi is always a constant number. Pi is an irrational number (a real number that can not be made by dividing two integers) and is known to be recited to more than 1000 decimal points.

Pi is used most commonly in maths to compute the area of circles: Pi is a fundamental component to the fields of mathematics and physics, therefore rightly has its own day where it can be celebrated by maths lovers around the world.

So what is pi exactly? Pi () is defined as the ratio of a circle’s circumference to its diameter where Pi is always a constant number. Pi is an irrational number (a real number that can not be made by dividing two integers) and is known to be recited to more than 1000 decimal points.

Pi is used most commonly in maths to compute the area of circles:

The volume of spheres:

And widely used in physics, notably Einstein’s field equation of general relativity.

## The History of Pi

Pi was first properly calculated by Archimedes 287-212BC (one of the greatest mathematicians) who approximated the area of a circle by using Pythagoras’s Theorem (a^2+b^2 = c^2), by drawing one polygon inside the circle and one polygon outside the circle.

The area of the polygon inside the circle can be defined as the lower bound as the area inside the polygon is equal to or greater than the circle and spaces remain. The area of the polygon outside the circle can be defined as the upper bound as the area of outer polygon is greater than the circle. As the circle lies in between the two polygons, the area must also lie between the polygons. He had found an approximation of pi within those limits and knew that the value lied in between 3 1/7 and 3 10/71.

## Why is Pi so interesting?

Having been around for over 3000 years, Pi is still one of the most researched topics in maths. Other numbers such as e (2.71828) can be calculated to a high degree of accuracy with few decimal points, however pi still seems to elude the best of mathematicians as the degree of accuracy increases ever more with increasing amount of digits.

Being an irrational number, and therefore infinite, some people have gone to lengths in reciting the digits of pi. In November 2005, Chao Lu attempted to recite the number and achieved a total of 67,980 digits. This took a staggering 24 hours and 4 seconds with no breaks as the time limit allowed between the numbers was only 15 seconds. He had planned to recite 91,300 digits although falling at the 67,981st hurdle.

## How to spend Pi day?

Here are some great ways you could spend Pi day:

**1. Memorising the number**

How much of the number can you memorise? Although pi is a never-ending number, knowing the first ten digits is more than sufficient in being able to accurately calculate the circumference of a circle to 1 centimetre. This year pi day will be celebrated on 03/14/15 at 9:26:53. A short phrase to help you memorise the first 10 digits is “Wow, I made a short memorable pi string, could you?” (Clue, count the number of letters in each word).

**2. Have a Pi(e) bake off**

Traditionally Pi day is celebrated by baking a pie with the added decoration of the symbol displayed on top. Why not have a mini competition, invite friends and family to find out who bakes the best pi?

**3. Reading books on Pi**

For those that love a good read. Sir Cumference and the Dragon of Pi, by Cindy Neuschwander and illustrator Wayne Geehan is a good read for children of all ages, solving multiple riddles that will reveal a cure. The magic lies in the discovery of pi and that is the same for all circles.

How will you spend Pi day?