*The State of the Tau 2023 is also available at tauday.com.*

Hey Google, when is Tau Day this year?

Ah, yes—that’s today. Happy Tau Day, everyone!

I’m Michael Hartl, founder of Tau Day and author of *The Tau Manifesto*. Thanks for joining me in the celebration of the true circle constant, tau:

As in previous years, I’ve made minor updates to *The Tau Manifesto*, Tau Day’s (and tau’s) founding document, which is available both online and as a print edition at Amazon. And as always, you can show your support for tau by wearing an Official Tau Shirt. You can even follow along with and share the day’s activities in real time using the #TauDay hashtag on Twitter.

Finally, I’m pleased to announce that I’ve started Michael Hartl’s Substack, a newsletter and blog that includes tau-related announcements (such as this one). As part of this, I’ve moved the main tau mailing list over from my old email software to Substack. As with any Substack, you can unsubscribe at any time using the link at the bottom of each message.

My Substack has both free and paid tiers, and my plan is to include tau-related news among the free posts. My plan for paid posts is to focus (at least initially) on math and math learning, including curated book and YouTube recommendations, as well as details about my current personal project to learn pure mathematics. (Clearly, I must know at least *some* math, but I’m planning to learn more. How much more, and why? Subscribe to find out!)

Without further ado, here are some of the highlights in the world of tau since Tau Day last year:

As the result of a collaboration with math YouTuber sudgylacmoe, there is now an amazing animated version of

*The Tau Manifesto*.Tau has been added to Liberty Eiffel, a free compiler for the influential Eiffel programming language, and (amazingly) has also been added to that 800-lb. gorilla of modern computing, the Java programming language.

I published

*Learn Enough Python to Be Dangerous*, which makes extensive use of`math.tau`

from the Python standard library.JSCAD, an open-source set of libraries to create 3D and 2D designs using JavaScript, comes equipped with a predefined constant TAU.

Aleksandr Alekseevich Adamov (who made the Russian translation of

*The Tau Manifesto*) passed along a link to a formalized proof that τ = 2π.For the second year in a row, SLMath (formerly MSRI) is running a Tau Day puzzle contest, with an Official Tau Shirt as a prize! In the spirit of “twice as much pie”, generous SLMath supporters are also matching any donations made through Tau Day 2023.

Read on for more details about these happenings. Enjoy!

#### The Tau Manifesto, animated version

Sometime early in 2022, I found the great video A Swift Introduction to Geometric Algebra by math YouTuber sudgylacmoe. It was created using manim, an open-source version of the animation software developed for the wildly popular 3Blue1Brown YouTube channel, and introduces the remarkable field of geometric (Clifford) algebra.

I thought sudgy’s video was fantastic, and I also happened to notice a delightful detail: it uses tau!

One of my favorite things about the video is that it doesn’t even bother introducing tau—it just goes ahead uses it, secure in the knowledge that viewers either already know about it or can figure it out from context.

I thought this use of tau was so cool, and enjoyed the video so much, that I actually tried to track down sudgy’s email address so I could reach out to him directly. Unfortunately, I was unsuccessful in this attempt, but fortunately sudgy himself emailed *me* on Tau Day last year!

Among other things, sudgy proposed collaborating on an animated version of *The Tau Manifesto*, which I thought was a great idea. The result, which just launched for Tau Day 2023, is available here:

The script for the video was adapted from the text of *The Tau Manifesto*, with both me and sudgy narrating, and the amazing animation is all sudgy. Thanks to sudgy for the enjoyable collaboration and for all the great work!

#### Java and Liberty Eiffel

Java and Liberty Eiffel have joined languages such as Microsoft .NET, Rust, and Python in supporting tau. Wow!

#### Learn Enough Python to Be Dangerous

À propos of the final language example in the previous item—namely, Python—I made extensive use of the `tau`

constant from Python’s standard math library in my recently published tutorial *Learn Enough Python to Be Dangerous* (book, videos, and online course, including the book’s print edition). In my previous tutorials on JavaScript and Ruby, I had to define `tau`

by hand, so it was deeply satisfying this time to have the support of the language itself. As noted in the book’s free first chapter, Python was the first language I really *loved*, and it’s great to get a little love back in return!

#### SLMath visit, Tau Day puzzle, and matching donations

On a recent trip to the San Francisco Bay Area, it was my great pleasure to visit the Simons Laufer Mathematical Sciences Institute (SLMath, formerly MSRI) on the campus of the University of California, Berkeley. I was there at the invitation of Uta Lorenzen, Assistant Director of Development, who greeted me wearing her own Official Tau Shirt! (As an extra bonus, and as Uta herself pointed out, her first name is an anagram for “tau”.)

As you can see if you look closely at the image above, the friendly folks at SLMath also gave me my own snazzy Tau Day medal, another of which will be awarded to the winner of the Tau Day Puzzle Contest (one day left to solve it!).

Thanks to Uta and to SLMath Director of Advancement and External Relations Annie Averitt for being such enthusiastic and gracious hosts during my visit. As noted above, generous SLMath supporters are matching donations made through Tau Day 2023. I hope you’ll join me and donate to SLMath/MSRI if you’re in a position to do so. Twice as many donations, twice as much pie!

#### Thanks again

Thanks again to everyone who has supported tau over the years. Here’s to many more years to come!

Michael Hartl

Founder, Tau Day

Author, *The Tau Manifesto*