Pi Day

According to Wikipedia, "In 1988, the earliest known official or large–scale celebration of Pi Day was organized by Larry Shaw at the San Francisco Exploratorium, where Shaw worked as a physicist, with staff and public marching around one of its circular spaces, then consuming fruit pies. The Exploratorium continues to hold Pi Day celebrations.

(The Exploratorium is "a museum of science, technology, and arts in San Francisco. Characterized as 'a mad scientist's penny arcade, a scientific funhouse, and an experimental laboratory all rolled into one', the participatory nature of its exhibits and its self–identification as a center for informal learning has led to it being cited as the prototype for participatory museums around the world." Larry Shaw was its Technical Curator from 1972 until his retirement in 2005. He died in 2017, aged 78.)

In 2009, the US House of Representatives supported the designation of Pi Day. UNESCO's 40th General Conference decided Pi Day as the International Day of Mathematics in November 2019.

... and there's more!

Pi Approximation Day is observed on 22 July (22/7 in European format) – 22 divided by 7 being a common approximation of π, dating from Archimedes and accurate to two decimal places. (22/7 = 3.143 to three decimal places; π itself is 3.142 to the same level of accuracy.)

Two Pi Day, also known as Tau Day for the mathematical constant Tau, is observed on 28 June (6/28 in American format).

What is "the mathematical constant Tau"? Well here it gets a bit technical.

Wikipedia informs us that "In 2001, Robert Palais [Wikipedia doesn't enlighten us any further] proposed using the number of radians in a turn [360°] as the fundamental circle constant instead of π, which amounts to the number of radians in half a turn, in order to make mathematics simpler and more intuitive."

(A radian is defined as "the angle subtended at the center of a circle by an arc that is equal in length to the radius of the circle." Click here for Wikipedia's explanatory animation.)

Got it so far? Right ... well Wikipedia continues: "In 2010, Michael Hartl [Wikipedia is no help here either] proposed to use tau to represent Palais' circle constant: τ = 2π." His reasoning was basically that the symbol for tau looks a bit like the one for pi (except that it has one leg instead of two).

So there are π radians in 180°, and τ radians in 360°. This is why both Robert Palais and Michael Hartl feel that tau (τ) is a better way of defining the relationship between the circumference of a circle and its diameter (or radius) than pi (π).

I have no information as to where the US House of Representatives or UNESCO stand on Two Pi Day (a.k.a. Tau Day) – or on Pi Approximation Day.

Albert Einstein was born on Pi Day (14 March) in 1879.