## Celebrating Pi Day!

Category: Events Pi has interested people around the world for over 4,000 years.  Many mathematicians – from Fibonacci, Newton, Leibniz, and Gauss – have toiled over pi, calculated its digits, and applied it in numerous areas of mathematics.

Sunday, March 14th marks Pi Day, and at Zemax, we want to take a moment to recognize this annual celebration of the mathematical constant π by sharing some of our favorite facts about pi.

Early decimal in approximations for pi were obtained various ways. In ancient Babylon, rope stretchers marking the locations of buildings and boundaries estimated pi to be 25/8 = 3.125.  The ancient Egyptians determined the ratio to be (16/9)^2 ≈ 3.16. The earliest calculations of pi were based around measurement.

• Archimedes, a Greek mathematician, was the first to use an algorithmic approach to calculate pi.  He drew a polygon inside a circle and drew a second polygon outside of the circle. He then endlessly added more sides to both polygons, getting closer and closer to the shape of the circle.  Having reached 96-sided polygons, he proved that 223/71 < pi < 22/7.

• Until 1647, Pi did not have a universal name or symbol. William Oughtred named it pi in his publication Clavis Mathematicae.

• The π symbol was introduced by William Jones, a Welsh mathematician, in 1706 and it was made popular by the mathematician Leonhard Euler. The Greek letter was adopted because it is the first letter of the Greek word, perimetros, which loosely translates to “circumference.”

• 3.14 spells PIE when reflected in a mirror.

• Since pi is an irrational number, we will never be able to find all the digits of pi. Until 2017 the record for the number of the total digits of Pi identified topped out at 500,000. This record was broken by a Swiss scientist that computed more than 22 trillion digits of pi. The calculation took over a hundred days.

• In 2015, a 21-year-old student memorized and recited pi to 70,000 places. This was done wearing a blindfold and took more than 9 hours!

• In 2008 a 150-diameter crop circle that appeared near the English village of Wroughton was found to be code for the first 10 digits of Pi.

• Pi Day is also Albert Einstein’s Birthday!

• Known as the Prince of Pi, Physicist Larry Shaw started celebrating 14 March as Pi day at San Francisco’s Exploratorium science museum.

• On March 12, 2009, the U.S. House of Representatives passed a non-binding resolution, recognizing March 14th as National Pi Day.

• While the United States celebrates Pi Day on March 14th, many mathematicians outside the United States celebrate Pi Approximation Day (also known as Casual Pi Day) on July 22nd or 22/7 (a way of working out an approximate value for Pi for use in rough calculations).

William L. Schaaf claims “Probably no symbol in mathematics has evoked as much mystery, romanticism, misconception and human interest as the number pi” Nature and History of Pi.

We hope you have enjoyed reading our favorite Pi facts and join us in celebrating π on Sunday!