Some people may be aware of Pi Day, the March 14th holiday whose shorthand, 3/14, matches the first three digits of the famous number, 3.14. But some mathematicians are saying that Tau, which is twice Pi, is the truer circle constant and worthy of celebration.

Thus, June 28, or 6/28, has been dubbed Tau day.

So how will you celebrate? During Pi day, high school math departments around the world gorge on pies in faculty lounges, so maybe Tau day should require twice as many pies. Or, you could just go to YouTube and play the Tau Day song, What Tau Sounds Like.


Tau supporters are almost militantly against Pi, the old most important number. The idea of Tau most famously comes from a 2001 essay called Pie is Wrong! by Bob Palais.Tauists claim that the Pi measurement is incorrect because it uses the length of the diameter of a circle, rather than the radius.

For all these years, we have been looking at the wrong number when we have been looking at pi. Pi simply isn't the most natural number that we should associate with a circle. The proper number is 2pi, or tau,  University of Leeds professor told Kevin Houston The Economic Times.

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Tau is also four letters after Pi in the Greek alphabet.