π

Today was Pi Day, a "holiday" in some countries. Very fitting for this event is a pie. D. cooked it, we all ate it. Delicious :)
Why 14th March as Pi Day? Because some people say month first, so March 14. March is the third month in the year, so that would be 3/14. And π is 3.14159...... (infinite). The number of decimal digits has no end, and there is no repetition.
Pi is a constant used in circles (and part of that). The circumference is measured 2πr. The circular area is πr².
What a coincidence: Albert Einstein was born 14th March, Stephen Hawking passed away 14th March.

In case you are interested: Euler's number (e) is another irrational constant (2.71828.....), the base of natural logarithms. Yes, I loved math.