Pi is at the very center of the human experience. It’s the number intrinsic to cycles. The rising and setting of the sun? Pi. The cycle of the moon? Pi. The seasons? Pi. The tides? Pi. The motions of the stars and the planets? Pi. Eclipses? Pi.

On a 2d axis, a point on the circle is represented by the horizontal distance (x) and the vertical distance ( y ). And there is an angle represented by how far you’ve traveled around the circle. There is a connection to this angle and the coordinates. If the angle is t, then your location on the circle is (cosine t, sine t). When you travel half way around the circle, you’ve traveled pi radians, and a full circle is 2pi radians. Then, the cycle repeats again as you travel around again.

I think we’re all familiar with the sine wave. It’s the vertical component of your location as you move around a circle. If you graph just that motion, you see a beautiful periodic wave that cycles forever, every distance of 2pi.

You can transform the sine wave to fit different kinds of periodic data. The stock market? Pi. Infection rates? Pi. Roller coaster paths? Pi. The length of a river? Pi. Biological mechanisms defining stripes on a zebra? Pi. A swing set? Pi. Your car’s transmission? Pi. The shocks on your car? Pi. Your steering wheel? Pi. The famous Euler probabilistic curve? Pi. Sound waves? Pi. Square waves used in synthesizers? Pi. Anything and everything cyclical involves Pi. Happy Pi Day!