Happy Pi Day! How are you celebrating the transcendental, irrational mathematical constant central derived from circles on 3/14/15 at 9:26:53? For me, it's going to be giggling over physicists engaging in an epic chalk battle, and devouring an apple-ginger pie.

Pi Day is the best reason ever to bake a pie for breakfast. Image credit: Mika McKinnon

Pi Day is an annual celebration where mathematical enthusiasts take advantage of the North American custom of writing the date month-day corresponding to the first few digits of pi. (Don't follow this custom with your dates? We can work with that.) This year is particularly exciting as even the year is cooperating for the next few digits, getting us all the way out to 3.141592653. Why celebrate Pi Day? Because it's fun. (Unless you're feeling Grinchy...)

The number pi is a simple geometric ratio: divide the distance around a circle (the circumference) by the distance across it (the diameter). No matter the size of the circle, the ratio will be the same: pi.

The Earth is circular, to first approximation. Image credit: Allen Pope via NASA

The number itself is irrational and transcendental. Consequently, it continues forever without repeating. Although it only takes the first 40 digits to provide enough accuracy for the most demanding scientific tasks, mischievous humans have calculated it to a few trillion digits for the simple reason that they can. And, of course, that means that the few and proud will undertake epic feats of memorization, like Matt Parker and Tibra Ali at the Perimeter Institute:

How can you celebrate?

As for me, my celebrations started a day early with friends and family checking in to share plans of what flavour pies they were baking and swap recipe tips.