# No, really, pi is wrong… The Tau Manifesto

### by Michael Hartl

Tau Day is an annual celebration of the circle constant $\tau = 6.283185\ldots$, which takes place every June 28 (6/28 in the American calendar system). To learn more about what $\tau$ is and why it is important, read The Tau Manifesto, or watch one of the tau videos below.