Traditionally, Pi Day is 14 March, because that is 3-14 and π~3.14 (except in Indiana where it was 3 for a short time – also mythically in Alabama and Tennessee). That tells you the approximate number as our calendar does not handle irrational numbers well. It also does not work in Europe where they sensibly order their dates hierarchically day-month-year.
It also does not describe at all is how we get to that value. π describes the relationship between the radius of circle (r) and its area (A) or circumference (C): A=πr2 and C=2πr. If we set the length of the year (365.25 days) as the area, the radius of our year circle is 11 days. The 11th day of the year is, not surprisingly, 11 January.
I personally prefer to celebrate Pi Day as recognized by the circumference tradition on 27 February (r=58), but to each their own.
As you may not be aware, we have declared today, 14 August, to be Phi Day. Here at The Finch & Pea we don’t go in for the superficial assignment of such days to the date that looks like the estimated value of important numbers in your particular dating system (eg, putting Pi Day on 14 March).
Phi is also known as the Golden Ratio. While it can be expressed as the number 1.618…, Phi is an irrational number, which means that the decimal portion goes on infinitely without repeating. So, any simple numerical expression is just an estimate and does not represent the true meaning of the number.
Phi represents a particular ratio of segments. If we take the regular pentagram (composed of lines of equal length) on the right. The ratios of red:green, green:blue, and blue:pink are all equal to Phi.
If we imagine that the year is a line that is 365.25 days long, we can divide it into two segments whose ratio to each other is Phi. Dividing at Day 226 gives us the ratio 226/139.25 = 1.623*.
The 226th day of a regular calendar year is 14 August*. Happy Phi Day!
*Ideally, we’d go for Day 225.75, which is 6PM on 14 August, but then we’d have to decide on a time zone.
**In a regular year, 226/139 = 1.625. In a leap year, 14 August is Day 227, which gives us 227/139 = 1.633. 13 August is a bit better in a leap year (226/140 = 1.614); but I think there is something to be said for a consistent day on the calendar.