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 $\tau$ (tau) is and why it’s important, read The Tau Manifesto, or watch one of the tau videos below.

To get all the latest updates on tau, read the State of the Tau newsletter, and join the official tau email list.

Tau Videos

About the author

Tau Day founder Michael Hartl is an author, educator, and entrepreneur. He is the creator of the Ruby on Rails Tutorial book and screencasts, one of the leading introductions to web development, and is cofounder of Learn Enough to Be Dangerous and the Softcover publishing platform. Previously, he taught theoretical and computational physics at Caltech, where he received the Lifetime Achievement Award for Excellence in Teaching and served as Caltech’s editor for The Feynman Lectures on Physics. He is a graduate of Harvard College, has a Ph.D. in Physics from the California Institute of Technology, and is an alumnus of the Y Combinator entrepreneur program.

Michael is ashamed to admit that he knows π to 50 decimal places—approximately 48 more than Matt Groening. To atone for this, he has memorized 52 decimal places of τ.