Celebrating Tau Day
Written by Sue Gee   
Wednesday, 29 June 2022

Today is June 28 or 6.28. Is that a familiar number? Probably not. It's called tau and it is twice a number that is remembered - 3.14, called pi, which we've got used to celebrating on Pi Day - March 14. The good news is that as tau is two times pi it gives us a great excuse to eat a double helping.

Tau Day originated in 2010 when, on June 28, Michael Hartl published the Tau Manifesto which advocates that the "true" circle constant is the ratio of the circumference of the circle to its radius and that this should be called by the Greek letter tau: 


Hartl may have designated the day but the concept of replacing pi with the alternative that is essentially pi times two came from University of Utah Professor of mathematics in an article titled π is wrong! in the Mathematical Intelligencer in 2001Another keen advocate of Tau is Vi Hart who made this video explaining why tau should be preferred for Pi Day 2011: 

The main reason Hartl and other proponents of tau have for preffing it is that it is less confusing than pi, something he demonstrates with this diagram:


So if tau is so superior to pi why don't we all know about it and use it? Good question - or is it? Tau is the equivalent of 2pi and has all the same marvellous properties - it is a fundamental constant of nature found not only in circle relationships but in everything to do with rotation and even the Einstein equation. It is both irrational and transcendental - and to know about this I refer you to one of I Programmer's previous articles, Celebrate Pi Day It Contains All Human Knowledge

Will we ever find Google looking for the quadrillionth digit of tau rather than that of pi? Probably not since the tradition of breaking world records tends to perpetuate the familar. Everything we know about pi carries over to tau, just by multiplying by 2. Now we know that the 100 trillioneth digit of Pi is 0, the corresponding digit of tau must either be 0 or 1 - and if you give me Pi to nine digits I can give you tau to eight digits.

If you are beginning to feel boggled by the idea that any number sequence you can imagine must be included in tau an infinite number of times, just go and seek out a pie and have a double portion. Guaranteed to make you feel better.


More Information

The Tau Manifesto

Fun Holiday – Tau Day

Related Articles

Happy Pi Day!      

Pi Day 2022 - It's Irrational!!! 

Pi Day 2021 - Give Me Pi!

Pi Day 2020 - A Meditation On Numbers

Celebrate Pi Day It Contains All Human Knowledge   

New Record From Google - 100 Trillion Digits Of Pi 

Finding Pi

The Programmer's Guide To The Transfinite 

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Last Updated ( Wednesday, 29 June 2022 )