Pi, Greek letter (), is the symbol for the ratio of the circumference of a circle to its diameter. Pi = 3.1415926535... Pi Day is observed on March 14 (3/14), due to π being roughly equal to 3.14. Pi Approximation Day is observed on July 22, due to π being roughly equal to 22/7. Wikipedia.
Some also celebrate Pi Approximation Day in addition to Pi Day, which can fall on any of several dates:
- April 26: The Earth has traveled two radians of its orbit by this day (April 25th in leap years); thus the entire orbit divided by the distance traveled equals pi
- July 22: 22/7 in the more common day/month date format, an ancient approximation of pi
- November 10: The 314th day of the year (November 9 in leap years)
- December 21, 1:13 p.m.: The 355th day of the year (December 20 in leap years), celebrated at 1:13 for the Chinese approximation 355/113