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.
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Buy Ebook and Videos
Buy the downloadable ebook versions of The Tau Manifesto in EPUB, MOBI, and PDF formats, along with downloadable versions of the Tau Talk videos!
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Get your own Tau Tee
Celebrate Tau Day in style with a Tau tee shirt, available only for a limited time from Teespring. Offered in both men’s sizes as well as fitted women’s.
Tau Videos
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Original Tau Talk (short version)
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Original Tau Talk (long version)
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The Tau Manifesto | Talks at Google
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What Tau Sounds Like
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Pi Is (still) Wrong
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Tau replaces Pi (Numberphile)
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.