Tau Day

Tau Day is a mathematical holiday celebrating an alternative to the well-known constant π (pi), which represents the ratio of a circle’s circumference to its diameter, approximately 3.14. While π has its own holiday on March 14, mathematics professor Robert Palais of the University of Utah proposed a more accurate constant to describe the relationship between a circle’s circumference and its radius. This alternative constant, known as 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 for the use of 2π as a more natural constant in mathematics. This idea was later embraced by Michael Hart, a Harvard-educated physicist with a Ph.D. from the University of California. In 2010, Hart published *The Tau Manifesto*, formalized the use of tau (τ) as the circle constant, and established Tau Day. The date, June 28, reflects the numerical value of tau (6.28), just as Pi Day reflects the value of π.

Interesting Facts

• Michael Hart’s *The Tau Manifesto* has been translated into seven languages and continues to gain international recognition.
• Tau supporters argue that tau simplifies mathematical expressions, making formulas more intuitive and elegant.
• The holiday is celebrated by mathematics enthusiasts worldwide, often with creative food, games, and educational events.

How to Take Part

Tau Day is a fun and engaging way to explore mathematics and its applications. Here are some ideas to celebrate:

1. Embrace the culinary tradition of Pi Day by doubling it—enjoy a cake twice as large or a pizza as big as your appetite allows, symbolizing tau’s value being twice that of pi.
2. Host math-themed games or competitions for kids and friends. Discuss the latest mathematical discoveries or explore why tau might be better than pi.
3. Share educational posts about Tau Day on social media to spread awareness of this fascinating mathematical concept.

When is Tau Day in 2025?

Tau Day is observed annually on June 28.

Observations