Tau

Tau is the nineteenth letter of the Greek alphabet. It looks like a capital T (Τ) or a small t (τ). In Greek, this letter makes a "t" sound, like in the English word "top." People use Tau in many different ways, just like our letter T.

In old times, the Greeks got the idea for Tau from a letter called taw used by the Phoenician letter. Over time, Tau helped create other letters, like our T in the Latin alphabet and a letter called Te in the Cyrillic alphabet.

When Greeks used letters for numbers, Tau stood for the number 300. Even today, Tau is important for scientists, mathematicians, and anyone learning about the Greek alphabet.

Modern usage

See also: Greek letters used in mathematics, science, and engineering § Ττ (tau)

The lower-case letter τ is used as a symbol for many different ideas in science and math.

Biology

The time it takes for an animal's daily cycle to repeat when there is no light or dark.
The time between doses of medicine in the body.
A main idea in a theory about how things change over time.
A protein that helps tiny parts inside cells stay in place, linked to some diseases like Alzheimer's disease.

Mathematics

A way to count the number of ways to divide numbers.
A special number in math and science.
The golden ratio, though another symbol is used more often.
A measure of how related two sets of numbers are.
A point in processes that change over time.
The ratio of a circle's distance around to its radius, which is twice π.
Special math functions.
How much a curve twists.
Moving things in flat shapes.
A number related to patterns in math.

Physics

The time it takes for something to happen in space.
The force that makes things twist.
How long a light wave lasts.
A tiny part of atoms.
How much sunlight can get through the air.
A symbol for time in science.
How long it takes for something to change, like in electric circuits.
The turning force on objects.
A symbol for how twisty paths are.
Energy linked to temperature.

Symbolism

In ancient times, the letter tau stood for life or resurrection, while another Greek letter, theta, was linked to death. During Biblical times, a mark called the taw was used to show who was sorry for their mistakes.

The shape of tau is similar to a cross. This connection goes back to very old writing systems. A funny story from around 160 AD talks about a disagreement between two letters, where one claims the other should be punished for its shape.

Tau is also an important symbol for some religious groups, especially those who follow the teachings of St. Francis. Many of their churches show a special tau sign.

Today, tau is also used in astronomy to represent Titan, one of Saturn's moons.

Unicode

The Greek letter Tau has special codes used in computers and writing. These codes help show the letter correctly in different places.