Tau Day

Tau Day is a mathematical holiday that celebrates an alternative to the famous constant π (pi), which represents the ratio of a circle’s circumference to its diameter (approximately 3.14). While Pi Day is observed on March 14, mathematics professor Robert Palais from the University of Utah proposed a more natural constant based on the circle’s radius rather than its diameter. This constant, called tau (τ), equals 2π—approximately 6.28—and is celebrated annually on June 28.

History

In 2001, Robert Palais published the article “π is Wrong” in the journal The Mathematical Intelligencer, arguing that using 2π provides greater mathematical clarity. The idea was championed by physicist Michael Hart, who later published The Tau Manifesto in 2010. Hart officially proposed the adoption of tau and introduced Tau Day, choosing June 28 as its date to reflect the value of tau (6.28), much like Pi Day corresponds to 3.14.

Interesting Facts

• Michael Hart’s The Tau Manifesto has been translated into at least seven languages and is widely read in math circles.
• Supporters of tau claim it simplifies many mathematical formulas, making them more elegant and easier to understand.
• Tau Day is celebrated by math enthusiasts with themed games, food, and discussions about geometry and constants.

How to Take Part

Here are some ways to get involved in the celebration of Tau Day:

1. Double the fun of Pi Day—bake a cake or pizza twice as large to symbolize tau being twice pi.
2. Organize math challenges or trivia with friends and family to spark curiosity about mathematical constants.
3. Share facts and graphics about Tau Day on social media to promote awareness and education.

When is Tau Day in 2025?

Tau Day is observed every year on June 28.

Observations