Tau Day 2025 – Significance, Memes, Quiz

Tau Day is widely recognized on June 28. On June 28, 2010, “The Tau Manifesto” launched at the equal time due to the fact the primary Tau Day. “The Tau Manifesto” was a book written by Michael Hart that was dedicated to the lesser-known number. In it, pi is referred to as unnatural and confusing.

Michael Hartl was an educator, entrepreneur, and author when he created this holiday and he had previously taught computation and theoretical physics at Caltech (California Institute of Technology). Pi compares a circle’s circumference with its diameter, and many mathematicians are disinterested in this quantity whereas tau is the number that connects a circumference to that quantity. The day is used to celebrate all of mathematics, but tau specifically still has an uphill battle in receiving recognition.

Tau or τ, is equivalent to 2π, or 6.28318530… That makes today, June 28th, the perfect day to sing its praises. Michael Hartle, author of “The Tau Manifesto,” believes tau is more important than pi because circles are more naturally defined by their radius than their diameter. In addition to being found naturally in equations used in a wide variety of engineering and mathematics applications, tau is a more perfect constant to represent the perfect circle. In this article, we will discuss Tau Day 2025 History, Quiz, and more.

Tau Day 2025 Date –  June 28

In this article readers can get a glimpse on

• History and Significance of Tau Day
• Tau Day Facts and Memes
• Tau Day Quiz

What is Tau?

The constant is numerically equal to 2*pi (2 times pi), and with value approximately 6.28. The ratio equates to 2*C/D. Where C is circumference and D is diameter of circle.

Applications of Tau 

• There are many expressions that actually require “2*pi” calculation, having tau being equal to that simplifies them to great extent, for e.g. Circumference of circle = 2*pi*r = tau*r.
• Concept of tau can be useful in angular measurements like angles in radians, representing a complete “one-turn” and cosine functions in trigonometry have periods of tau.
• These concepts can be useful for teaching geometry as would reduce the confusion of using “pi” and “2*pi” at many applications and would help get rid of factor of 2.
• Tau simplifies Euler’s identity by eradicating the factor of 2.
• It is useful at many places where “2*pi” are used such as Fourier transforms, Cauchy integral formulas etc.

Replacing Pi

• The concept of replacing pi by tau as a better way to describe the relationship between a circle’s circumference and its radius was first brought up by mathematics professor, Bob Palais in the Mathematical Intelligencer in an article called π is wrong!.
• The Tau Manifesto by physicist Michael Hartl. Both of these articles called for the replacement of pi by tau. Tau, the ratio of a circle’s circumference to its radius, is equal to 2 π or 6.283.

Interesting Facts on This Day

Tau of old – In ancient times, tau was used as a symbol for life or resurrection.

Double dates – Tau comes to the number (6.28) is twice as much as pi (3.14) which is why Tau Day is 6/28.

Ad Infinitum – Both tau and pi have an infinite amount of numbers.

Enough is enough – 39 digits are enough to calculate the circumference of a circle.

History of Tau Day

The first known use of tau was approximated by Archimedes in the third century. He was born in the Greek city-state of Syracuse on the island of Sicily. Archimedes was known as one of the greatest scientists of the classical age, who, among many other things, calculated pi to the most precise value known. Pi is defined as the ratio of a circle’s circumference to its diameter as is tau, but some believe that Archimedes’ work would have been all the better if he had relied more on tau than pi.

During the eighteenth century, Leonhard Euler used the Greek letter π to represent the ratio of pi itself and for many years it has remained as the quintessential constant circle. This helped people understand circles, triangles, and other principles of geometry. It was a useful device that served its purpose well, but a new voice would define it as inelegant a couple of centuries later.

The tau movement was founded by the former University of Utah math professor Robert Palais who believed that tau simplified the math. Palais noticed that something was off with pi when calculating the sine of π/2 and the image he saw didn’t add up to the calculations. From this, he knew that pi wasn’t the way. Palais published his findings in a 2001 article titled “π is Wrong” in the “Mathematical Intelligencer.” He noted that Euler went back and forth between tau and pi, but pi became the accepted constant. Palais then proposed tau was superior and he used the pi symbol with an extra leg to represent it, and it eventually became an uppercase T.

The Tau Manifesto is dedicated to the proposition that the proper response to “π is wrong” is “No, really.” And the true circle constant deserves a proper name. As you may have guessed by now, The Tau Manifesto proposes that this name should be the Greek letter τ (tau):

Tau Day Significance

• Tau (uppercase/lowercase Τ τ), is the letter of the Greek alphabet, used to represent the “t” sound in Ancient and Modern Greek.
• The value of tau is twice the value of pi, proponents of tau day call for “twice as much of pie”
• people want to use Tau in place of Pi, the special number that comes from circles. Tau would be equal to two times pi, or about 6.283.
• These people want to use Tau because they think it would be easier for everyone to understand. There are many reasons in math why Tau could be useful or helpful. One of the simplest is that it would make learning about radians easier.
• A radian is a way of measuring the angle of a circle. It says that the number of radians in an angle is equal to the length of the outside of the circle, or the ‘arc length’, that is covered by an angle, divided by the radius, or distance from the point in the center of a circle to anywhere on the outside (see the picture on the bottom right of the page).
• If the distance covered around the outside of a circle is equal to the radius, than one radian is being covered. Around the whole outside of a circle, there are about 6.283 radians – or, Tau radians (Tau is just a number, like 0, or 7, or 100).
• The advantage of this is that one quarter of a circle would simply become Tau / 4 radians, and one half of a circle Tau / 2 radians, which is more in line with our intuition on circles (see also the drawing below).

Tau Day – Memes

• To eat circular shaped food. So, instead of one slice of pie, eat two or four.
• Tau is approximately equal to 6.28, so that makes today (6/28) tau day! Aside from eating twice as much pie as we would on 3/14.
• one of our awesome summer interns, all of our exercises that can be answered in terms of pi can now be answered in terms of tau too!
• Three points, one fork – Happy Tau Day
• Three cheers for Double pi.
• Tau sterilize humans! Human makes fewer kids cause fewer die!
• Tau try to negotiate!
• Tau player be like – They had us in the first half, Iam gonna lie.
• Stop trying to make Tau Day Happen – its not going to happen.
• Circle should be measured in Tau radians – Change my mind!

Tau Day Quiz 2025

1. What is the approximate value of Tau (τ)?

A) 3.14
B) 1.41
C) 6.28

Tau is not yet widely accepted within the scientific community, though there is a large community of scientists and technologists who have called for the replacement of pi by this symbol.

Since it contradicts with the symbols of torque, shear stress and time, this symbol has received a lot of criticism. We already had a ratio of “C/D” equal to pi, having another circle ratio with factor of two will create confusion in choice. There exist formulas which look more elegant as expression of “pi” rather than tau, for example, area of circle = pi*r*r = (tau*r*r)/2, introducing an extra factor of “1/2”.

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