On March 14 of every year, those of us who follow the North American custom of abbreviating dates as MM-DD (or MM/DD or MM.DD) celebrate Pi Day, in that 3.14 is an approximation of π. We do this, of course, by eating pie, which is an approximation of “pi.” Well, today is Tau Day, for the simple reason that tau (τ)—the ratio of a circle’s circumference to its radius—equals 2π, ergo 6.28 (and change): June 28. Now, I could tell you a whole story about how τ is a much better constant to celebrate than π, but you can’t eat a tau. What you can eat today is two pie(s).
Image credit: <a href="https://www.flickr.com/photos/andrewmalone/">Andrew Malone</a> [<a href="https://creativecommons.org/licenses/by/2.0/">CC BY 2.0</a>], via <a href="https://www.flickr.com/photos/andrewmalone/1276641014">Flickr</a>