Even now, a select group of mathematicians and mathophiles are counting down to what should (in my opinion) be one of the principal holidays on the mathematician’s calendar. You’ve all heard of Pi Day, some of you even celebrate it in one way or another (the number of my facebook friends signed up for “The Only Pi Day of Our Lives” surprised me), and it grieves me to say so, but it’s overrated. At best it should be a minor math holiday. If you celebrate only one circle-constant-related holiday in a year, it should be Tau Day. And if you use only one Greek letter as shorthand for a particular constant which is related to circles and mathematically ubiquitous, better that it be , the circumference of a circle with unit radius (approximately 6.28318531, which is twice that other number).

**Tau Day is 6/28 (by analogy with Pi Day Half Tau Day, 3/14), so our countdown stands at 6 days ( days, if you will).**

I won’t get into the details here, but the key contention is that τ, not π, is the circle constant we *should* focus on. Instead of (or ), it would be *better* to write . For a quick and cute introduction, check out the Pi is Still Wrong video from everybody’s favorite mathemusician, Vi Hart. For the whole manifesto, check out Michael Hartl’s wonderful site (updated a few months ago for ~~Pi Day~~ Half Tau Day).

Especially for the non-mathematicians here, “should” and “better” might seem strange word choices. Today I want to focus on what exactly they might mean in this context.

(Remark: If you’re more science-minded, this is a little like the oft-heard-in-some-circles assertion that the convention for positive and negative charges is “backwards”, the opposite of what it “ought to be”. Apropos xkcd comic!)