## Saturday, March 14, 2015

### Happy Pi Day of the Century

Every March 14, we celebrate Pi Day.  3.14 is a pretty good approximation, better than 1 part in 1000. This year, being 2015, we acknowledge 3.1415 in significant digits.  You can carry it out further at 9:26:53 AM and PM: 3.141592653.

Also this year, you can celebrate for another second to 9:26:54 because 3.1415926535… continues to 8979… So, 3.1415926536 is an acceptable estimate.

You can have a pretty good celebration next year, as 3.14159 rounds to 3.1416 , which is a better approximation than 3.1415.

The first 50 decimal digits of pi are 3.14159265358979323846264338327950288419716939937510 (Wikipedia here).

Pi Day dot org  gives many suggestions for circular festivities – and the first million digits of pi here.  And they sell a clock, with a circumference measured out in radians or fractions of pi.

The formula for the circumference of a circle is pi times the measure of the diameter: pi times d.  We usually learn C = 2 pi r first because twice the radius (2r) is the diameter, and we usually draw a circle with a compass by measuring the radius.
So, half way around a circle (180 degrees) measures pi. All the way around (360 degrees) is 2 pi.  90 degrees is pi/2 …  45 degrees is pi/4… 30 degrees is pi/6 or one-twelfth of a circle or 1 o’clock.

We use the lowercase Greek letter pi because it begins the Greek words “perimeter” (“measure around” perimetron) and “periphery” (“carry around” perifero). It is something of a modernization because Euclid, Archimedes, and the other ancients only had what we now call capital letters.  The lowercase letters were invented in the Middle Ages.

(The Middle Ages followed the Dark Ages, which is where software applications management and marketing teams live permanently.  Blogspot has no Symbol font; neither does WordPress.  We live in an age of ignorance. Seeking a personal Renaissance, I have a year to figure out the CSS and code my own or find a plug-in, sort of like when the West learned Arabic numerals.)

Also on Necessary Facts