March 14, 2015 has been labeled the Pi Day of the Century because of the way this day is abbreviated, at least in America: 3/14/15.
I was recently asked an interesting question: did any of our ancestors observe Pi Day about 400 years ago on 3/14/1592? The answer is, I highly doubt it.
My first thought was that may not have been known to that many decimal places in 1592. However, a quick check on Wikipedia (see also here), as well as the book “ Unleashed,” verifies that my initial thought was wrong. In China, 7 places of accuracy were obtained by the 5th century. By the 14th century, was known to 13 decimal places in India. In the 15th century, was calculated to 16 decimal places in Persia.
It’s highly doubtful that the mathematicians in these ancient cultures actually talked to each other, given the state of global communications at the time. Furthermore, I don’t think any of these cultures used either the Julian calendar or the Gregorian calendar (which is in near universal use today) in 1592. (An historical sidebar: the Gregorian calendar was first introduced in 1582, but different countries adopted it in different years or even centuries. America and England, for example, did not make the switch until the 18th century.) So in China, India, and Persia, there would have been nothing particularly special about the day that Europeans called March 14, 1592.
However, in Europe (specifically, France), Francois Viete derived an infinite product for and obtained the first 10 digits of . According to Wikipedia, Viete obtained the first 9 digits in 1579, and so Pi Day hypothetically could have been observed in 1592. (Although Unleashed says this happened in 1593, or one year too late).
There’s a second problem: the way that dates are numerically abbreviated. For example, in England, this Saturday is abbreviated as 14/3/15, which doesn’t lend itself to Pi Day. (Unfortunately, since April has only 30 days, there’s no 31/4/15 for England to mark Pi Day.) See also xkcd’s take on this. So numerologically minded people of the 16th century may not have considered anything special about March 14, 1592.
The biggest obstacle, however, may be the historical fact that the ratio of a circle’s circumference and diameter wasn’t called until the 18th century. Therefore, both serious and recreational mathematicians would not have called any day Pi Day in 1592.