Tau Greek Letter: Investigating This Symbol

Tau Greek Letter
In ancient times, the tau Greek letter symbolized life and resurrection. In the Phoenician alphabet, tau is the letter T. Today, it's commonly seen on college campuses among Greek organizations.

Tau Background

There are 24 Greek letters or alphabets that are 2,500 years old. They are commonly used in mathematics, science, and engineering. One common Greek letter is tau, the 19th letter of the Greek alphabet.  

Tau is written this way in Greek: ταυ

The letter takes root from the taw letter, the last in the Phoenician alphabet. Taw came from the Egyptian hieroglyph, which means mark. Tau represents 300 in the Greek numeral system. 

tau greek letter
The Greek letter ‘tau’ shares a similar resemblance and pronunciation to the letter ‘T’. It also commonly functions as a symbol in math.

What is the Symbolic Meaning Of Tau?

In ancient times, tau was the symbol of life or resurrection. Along with chi, tau is also a symbol of the cross in Christianity. It is the equivalent of the very last letter in the Old Hebrew alphabet and Phoenician and was originally in the shape of a tau cross. 

Tau Cross Symbol

The letter tau bears resemblance to a Roman cross, which is an important symbol for Christians because of the crucifixion of Jesus Christ. Because of its resemblance to the cross, St. Francis of Assisi used the symbol of the tau as his own seal.

Drawing from Ezekiel 9:4, the tau was also a sign place on the foreheads of the poor in Israel as a sign that they would be saved.

greek letter tau
Since it is connected with both the cross and the idea of resurrection, the Tau is a common symbol in Christianity.

Modern Use of the Tau Greek Letter

The ancient letter tau has several uses in the modern world as well. Mostly commonly, it functions as a symbol in a number of mathematical and scientific equations.


In math, the constant tau is numerically equal to 2 times pi or 2 * pi. The value of the constant comes out to be approximately 6.28. The ratio also equates to 2 * C/D, where D is the diameter and C is the circumference. 

Many expressions need 2 * pi calculation, but having tau equal to the value helps simplify them significantly. It comes in use when calculating the circumference of a circle with 2 * pi * r = tau * r. 

Angular Measurments

The concept of tau also proves helpful when it comes to angular measurements for angles in radians since it represents a one-turn. In trigonometry, cos and sine functions have a period of tau.

Simplifying Euler’s formula

Tau can also help reduce the confusion around pi while teaching geometry. Instead of wondering whether to use pi or 2 pi in many applications, you can use tau and also get rid of the 2 factor. By eliminating the factor of 2, tau also simplifies Euler’s formula. 

Other Mathematical Uses


The Greek small letter tau is one letter that has many uses in the world of physics as well. Physicists typically use tau to indicate a type of stress – shear stress.

Other Significance

Tau is used in other physics concepts, such as:

  • Transmission factor
  • Time-phase displacement
  • Thomson coefficient
  • Propagation constant
  • Time constant

Proper Time

Tau represents a movement through time measured with respect to any moving object, known as proper time. Proper time doesn’t depend on a stationary onlooker’s watch. 

Scientist Albert Einstein used tau in a relativity paper that describes the way two synchronized clocks will show different times if one clock moves at an appreciable fraction of the speed of the light and returns. 


In the context of biology, tau is known as Microtubule Associated Protein Tau (MAPT). Mainly expressed in neurons, the main function of tau is the stabilization of microtubules in axons. 

The MAPT gene consists of 16 exons and lies on the 17th chromosome. It has implications for neurodegenerative diseases like Alzheimer’s. 

It is the core variable theory in general tau theory, and in pharmacokinetics, tau is the dose interval.  

Greek Letter Tau in Popular Culture

Greek letters are commonly seen in sororities and fraternities. For example, the Greek letter tau is used in the sorority Alpha Theta Tau, which was founded in 1899.

Why Do Sororities and Fraternities Use Greek Letters?

The first fraternity, Phi Beta Kappa, was founded at the College of William & Mary in 1775. In order to keep the organization exclusive and secretive, its members began using Greek letters when talking about it.

The thought was that only highly intelligent people would be able to detect what was being said, which kept the group elite. Nowadays, Greek life is synonymous with the college experience in the United States.

The Greek alphabet tau has numerous meanings, ranging from ancient times to modern science. It is a important symbol in biology, physics, mathematics, and even character encodings.  

Interested in learning about more symbols and their meanings? Check out this article on the Fleur de Lis Flower!


Vanessa's liberal arts background has prepared her well for Symbol Scholar. A self-proclaimed theology nerd, Vanessa has interests in world religions, Reformation theology, history, and more. When she's not working, Vanessa enjoys spending time with her family, reading, exercising, and watching professional basketball.

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