Today marks the second annual celebration of pi’s nemesis, tau, which is two times the size of pi: 6.28 — which handily enough is today, June 28. Tau is identical to pi in every way, it’s just twice as large, which apparently makes it a far more coherent companion for circlesque calculations. Tau Day is designed to raise tau’s recognition, and is directly pitched against Pi Day, March 14.

The creator of Tau Day, Michael Hartl, says he was initially sparked into action by Robert Palais’ controversial 2001 article “Pi is wrong!“. Palais argues that pi is fundamentally confusing and unnatural for the sake of circle-related maths. Pi is derived from the diameter of a circle — but that’s counterintuitive, as a circle is actually defined by a set of points that are a fixed distance from the center, i.e. the radius. This results in the massive prevalence of 2π throughout mathematics. Tau (the Greek letter τ), then, in an effort to make maths more natural, is the ratio between the circumference and the radius, which comes out to 6.283185307179586… or exactly twice pi. Tau Day proposes that instead of using 2π, we just use 1τ.

Instantly, upon embracing tau, many types of pi-related trigonometric algebra become a lot easier. From Gaussian distributions to Fourier transforms, and even to the teaching of basic maths in school, tau makes the underlying maths simpler and easier to grok. Tau completely overhauls the counterintuitive relationship between pi and radians, and also circle functions like sine and Euler’s identity.

If you need more convincing, Hartl has created The Tau Manifesto, a very large document that details all of the reasons that tau is superior to pi. He reckons that it would be almost trivial to usher in a new age of tau-based mathematics — “if you are smart enough to understand radian angle measure, you are smart enough to understand τ” — and the document also details (with a few puns) why we use tau τ and not another Greek letter.

Finally, if you want to hear what tau sounds like, to 128 decimal places, Michael Blake has created the following video to celebrate Tau Day.