Tau Day

Tau Day is a mathematical holiday that highlights an alternative to the well-known constant pi (π), which represents the ratio of a circle’s circumference to its diameter (about 3.14). While Pi Day is observed on March 14, mathematics professor Robert Palais of the University of Utah argued for a more natural constant based on the circle’s radius rather than its diameter. This constant, called tau (τ), equals 2π (about 6.28) and is celebrated each year on June 28.

History of Tau Day

In 2001, Robert Palais published the article “Pi Is Wrong” in the journal The Mathematical Intelligencer, arguing that using 2π provides greater mathematical clarity. The idea was later promoted by physicist Michael Hart, who published The Tau Manifesto in 2010. Hart proposed adopting tau and helped popularize Tau Day, with June 28 chosen to echo the value 6.28, similar to how Pi Day corresponds to 3.14.

Interesting Facts About Tau Day

• Michael Hart’s The Tau Manifesto has been translated into multiple languages and is widely read in math circles.
• Supporters of tau argue that it can make many formulas more straightforward and intuitive.
• Tau Day is often marked with themed activities, food, and discussions about geometry and mathematical constants.

How to Take Part in Tau Day

Here are a few ways to participate in Tau Day:

1. Make a “double-sized” treat compared to Pi Day, such as a larger cake or pizza, to symbolize tau being twice pi.
2. Organize math challenges or trivia with friends or family to spark curiosity about mathematical constants.
3. Share facts or graphics about Tau Day on social media to encourage interest in math.

When is Tau Day in 2026?

Tau Day is observed every year on June 28.

Observations