Ten decimals are sufficient to give the circumference of the earth to the fraction of an inch, and thirty decimals would give the circumference of the whole visible universe to a quantity imperceptible with the most powerful microscope. — Simon Newcomb
![[Energizer Bunny]](http://cowpi.com/journal/media/2006/energizer-bunny-pi.jpg "Energizer Bunny with Pi on the drum")
It’s March 14, and any student of mathematics should recognize today as Pi Day. Mathematicians do not get many days in the year to celebrate math, but here is one.
π is defined as the ratio of the circumference of a circle and its diameter. π is called an irrational number because it cannot be written as a rational number, like fractions. The ancient Greeks thought fractions were rational and logical (most modern people, especially students beg to differ). The irrational numbers were considered illogical. As I tell my students, π is the Queen of the Irrationals because it is the most famous of the irrational numbers.
When irrational numbers are written in decimal form, their digits do not terminate and do not repeat with no patterns. Kinda crazy. (Rational numbers either terminate or repeat.) That means irrational numbers are the Energizer Bunny of decimal numbers—they keep on going and never end. The current record for the most known decimal places of π is 1.241 trillion digits!