Happy Pi Day!

Today, 3/14,  is Pi Day.  Pi (π) is the mathematical constant that is the ratio of a circle's circumference (C) to its diameter (D).  Any circle's circumference divided by its diameter is π, or approximately 3.14. 

It is approximately 3.14 because π actually is a number without end.  It has been computed to over 10 trillion digits.  Here is π to a thousand digits:

3. 14159 26535 89793 23846 26433 83279 50288 41971 69399 37510 58209 74944 59230 78164 06286 20899 86280 34825 34211 70679 82148 08651 32823 06647 09384 46095 50582 23172 53594 08128 48111 74502 84102 70193 85211 05559 64462 29489 54930 38196 44288 10975 66593 34461 28475 64823 37867 83165 27120 19091 45648 56692 34603 48610 45432 66482 13393 60726 02491 41273 72458 70066 06315 58817 48815 20920 96282 92540 91715 36436 78925 90360 01133 05305 48820 46652 13841 46951 94151 16094 33057 27036 57595 91953 09218 61173 81932 61179 31051 18548 07446 23799 62749 56735 18857 52724 89122 79381 83011 94912 98336 73362 44065 66430 86021 39494 63952 24737 19070 21798 60943 70277 05392 17176 29317 67523 84674 81846 76694 05132 00056 81271 45263 56082 77857 71342 75778 96091 73637 17872 14684 40901 22495 34301 46549 58537 10507 92279 68925 89235 42019 95611 21290 21960 86403 44181 59813 62977 47713 09960 51870 72113 49999 99837 29780 49951 05973 17328 16096 31859 50244 59455 34690 83026 42522 30825 33446 85035 26193 11881 71010 00313 78387 52886 58753 32083 81420 61717 76691 47303 59825 34904 28755 46873 11595 62863 88235 37875 93751 95778 18577 80532 17122 68066 13001 92787 66111 95909 21642 01989 ...

Some people have memorized it to over 67,000 digits!   There are even entire books published about pi1  It is used in all forms of mathematics and science including geometry, mechanics and electronics.  What fun!

Another very common use of π is to calculate the area of a circle: Area = π ×  r² where r² is the radius of the circle (or, half the diameter) times itself (or "squared").  There is a pizza chain in Wisconsin  (Rocky Rococo) that sells square pizzas because "pies are square."  Think about it.  Got it?

So today is Pi day.  Celebrate.  Eat pie. Pi Pie at Delft University:


 


Some very important people were born on Pi day .......... including Einstein.  He loved Pi.  So do I.