Pi Day is celebrated the last day of the second week in March because March 14 is the third month fourteenth day of the year and 3.14 is the most common approximation of pi. It was discovered by Archimedes of Syracuse. One way to celebrate Pi Day is to memorize pi to several decimal places. Or, eating a pie on March 14 is another good way to celebrate Pi Day. Any circular food like pizza, apples, or oranges will do because pi is used to determine the area and circumference of a circle.

Since 3.14159 is the first five decimal places of pi, doing something like blowing up balloons or blowing bubbles at 1:59 p.m. is a good idea. Pin the pi on the equation is a good game. Using equations that have pi in them like pi times the radius squared for the circle and pi times the diameter for the circumference might interest those proficient in mathematics. Writing a poem about pi to celebrate Pi Day could interest anyone interested in reading poetry.

Pi Approximation Day is July 22 because July 22 is the seventh month twenty-second day and 22/7 is a good approximation for pi: 3.142857… is the first six decimal places for the decimal representation for 22/7. The 142857 continues repeating forever because it is a rational number. November 10 is the 314th day most years, leap years November 9 is the 314th day. December 21 is the 355th day most years; leap years December 20 is the 355th day. The Ancient Chinese approximation for pi is 355/113=3.1415929… . Pi Day can therefore be celebrated at 1:13 p.m. on December 21 except for leap year when it should be celebrated December 20. Leap year is every four years; the last leap year was 2008, so the next leap year is 2012. Every year that is divisible by four is a leap year with the exception of years that are divisible by 100, although years divisible by 400 are still leap years (This is why the year 2000 was still a leap year even though it is divisible by 100).

Pi is 3.1415926535897932384626433832 7950288419716939937510 582097494459230781640628620899 86280348253421170679 to the first 100 decimal places. Its decimal representation is infinite, meaning the numbers do not stop. Pi is the ratio of the circumference of a circle to the diameter (circumference=pi times the diameter). The circle is pi times the radius squared.

Pi is an irrational number, which is a number that cannot be expressed as the ratio of two integers. This means the decimal representation of pi will not repeat integers over and over or terminate. Pi is also a transcendental number (not algebraic). Pi was known to the Egyptians, Babylonians, and Greeks in ancient times. Archimedes of Syracuse discovered the exact value of pi to be 3.14, but it is actually an infinite decimal. Pi was named pi because the Greek word for circumference starts with the Greek letter pi. The symbol pi was popularized by the Swiss mathematician Leonhard Euler. There are many projects attempting to calculate pi to millions and millions of decimals.