**By Douglas Fehlen**

### Fun with Numbers

Even those who abhor mathematics are familiar with pi, the mathematical constant that describes the ratio of a circle's circumference to its diameter. Pi Day, the annual celebration of this iconic number, takes place on March 14 because that date numerically represented is 3.14, pi's approximate value. People mark the occasion by baking pies, marching in circles and engaging in other idiosyncratic celebrations - like memorization contests to determine who can remember the most digits in pi.

While pi is beloved by many, it is not without its detractors. Bob Palais, a mathematics professor at the University of Utah, has written an article called 'Pi Is Wrong!' The piece, which appeared in an academic journal titled *The Mathematical Intelligencer,* suggests that 'the historical choice of the value of pi obscures the benefit of radian measure.' The fallout from this damning analysis: A better circle constant, Palais argues, would be the ratio of a circle's circumference not to its diameter, but its radius. In numerical terms, that's twice pi, or about 6.28.

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### Tau Day Is Born

While Bob Palais presented his criticisms of pi about a decade ago, the mathematics community has failed to leave the number by the wayside. It is still taught as the fundamental circle constant. Change, however, may be on the way. Last year, physicist and educator Michael Hartl published 'The Tau Manifesto,' an online article that incorporates many of the ideas presented by Palais. Hartl goes further than the professor, however, more forcefully suggesting that pi be abandoned for the circle constant he's called 'tau.'

Every circle constant, of course, deserves its day on the calendar, so Hartl has established 'Tau Day.' Observed on June 28 in honor of tau's approximate numerical value, the occasion is meant to promote greater acceptance of the number in the world of mathematics. Hartl is planning a party for this year's Tau Day, and he's encouraging others to do the same. 'If you think the circular baked goods on Pi Day are tasty,' he's said, 'just wait: Tau Day has twice as much pi.'

### Pi Still Tops as Circle Constant

Michael Hartl's tau has not yet overtaken pi for supremacy in the circle constant sphere, but others have expressed support on his website. One important convert: Bob Palais, the man who inspired Hartl to write 'The Tau Manifesto.' Both Palais and Hartl note the historical importance of pi but suggest that as math education moves forward, there is room to improve how its concepts are understood and taught. Tau, they suggest, is a step in the right direction.

For longtime lovers of pi, tau may never have the magical allure of 3.1459.... That doesn't mean, however, they can't join in the fun for Tau Day. In fact, many of the methods for celebrating Pi Day are applicable - we are still talking circles, after all. So bake a pie (or two!), march around in a circle or invite over fellow Math Olympiad alumni for a contest of who can remember the most digits in tau.

*Does talk of circle constants fill you with dizzying confusion? Brush up on your math skills with these blogs.*