The day has arrived. That one day on your calendar that you look forward to year after year. Yes, it’s Pi Approximation Day! …okay, even I can hear the crickets chirp. You don’t have to tell me that a day dedicated to the celebration of pi sounds a bit ridiculous. But that doesn’t mean that we shouldn’t be thankful for our knowledge of pi.

**A brief history of pi**

Pi is a mathematical constant equal to about 3.14 (but with a gajillion digits after). It’s a fixed ratio of the circumference and diameter of any circle. Pi is an irrational number, which means it can’t be expressed as a fraction of two whole numbers. There are a few decent approximations such as 22 divided by 7, hence why 22^{nd} of July is Pi Approximation Day.

We’ve know about pi since about 2000BC. There is evidence to suggest that both the ancient Egyptians and Babylonians had a pretty good approximation of pi, within 1% of the true value. However, it wasn’t until 250BC that the first calculation of pi was achieved.

The Greek mathematician Archimedes used polygons to approximate the area of a circle and hence calculate pi. Today though, we have computers to do calculations for us! Thanks to some clever algorithms and countless robot lives, we now know pi to over a trillion digits.

**More than a number**

But knowing pi to that many decimal places is pretty useless. Applying pi knowledge is far more important. As pi has been around for 4000 years, it is one of the oldest researched topics of all time, embedded in almost every facet of our society.

Pi has been so integral to our civilization, that it’s even thought that the ancient Egyptians used pi to help construct their pyramids. Today, applications are just as significant. Pi is used in engineering to construct components and control moving parts. It’s used in astronomy and astrophysics to calculate orbits and sizes of heavenly bodies. It’s even used in TV and radio to optimize signals that are sent to your home.

Beyond the physical world, pi can also be seen as a pillar for the power of human cognition. There are some people, sometimes referred to as ‘pi poets’, who have set bench marks for human memory capabilities by memorizing pi to many thousands of digits. The current Guinness World record holder is Lu Chao from China, who can memorise pi to over 67,000 decimal places!

**Easy as Pi**

Lu Chao and others like him use mnemonic techniques to remember digits. One of the most common mnemonic techniques used is to create a story or poem, with the letter length of the word corresponding to a number. For example ‘Pie, I want a whole allotment of pretty tasty pie’. The first word has three letters, the second word has one letter and so on. The sentence corresponds to the first 10 digits of pi: 3.141592653 (although one must remember we’re talking pie, not pi)

The fact that we can apply mnemonic techniques to memorise pi to such lengths is a testament to human achievement (albeit Lu Chao probably had too much time on his hands…). Even more impressive is our ability to translate these mnemonic techniques to other academic spheres. Author Mike Keith wrote an entire book using the first 10,000 digits of pi. Whether that’s genius or madness is up to you. Either way, it’s pretty impressive.

**Celebrate, have some pie**

So what will you be doing this Pi Approximation Day? Reflecting on pi while eating some pie? Why not try creating your own mnemonic story using pi. Perhaps you could create a haiku to enter into the annual RiAus Sci-Ku Competition?

Whatever it is you do, let us know in the comments. Happy Pi Approximation Day! And as Rebecca Black would say ‘Its Pi Day, Pi Day, gotta get down on Pi Day’.