Today is Pi Day
Written in the USA date format, March 14 is an unofficial celebration for Pi Day derived from the common three-digit approximation for the number π: 3.14. It is usually celebrated at 1:59 PM (in recognition of the six-digit approximation: 3.14159). Some, using a twenty-four-hour clock rather than a twelve hour clock, say that 1:59 PM is actually 13:59 and celebrate it at 1:59 AM or 3:09 PM (15:09) instead.
Pi Approximation Day is one of two days: either July 22 (written 22/7 — in commonwealth/international date format— 22 divided by 7 is an approximation to π), or April 26 (April 25 on leap years), the day on which planet Earth completes two Astronomical units' worth of its annual orbit: on this day the total length of Earth's orbit, divided by the length already traveled, equals π (that is, the Earth has travelled two radians in its orbit).
Another day of approximation is on the 355th day of each year at 1:13pm, based on the approximation value of 355/113 derived by Zu Chongzhi.
Another Pi Approximation Day is November 10 (or November 9, depending on whether it is a leap year or not.) This is the 314th day of the year on the Gregorian calendar.
Many mnemonics have been devised for remembering the digits of pi, consisting of phrases or verses in which successive digits of pi are obtained by counting the number of letters in each word. (Fortunately, the first thirty digits of pi contain no zeroes). Some are:
- "How I wish I could recollect pi easily today." (3.14159 265)
- "How I want a drink, alcoholic of course, after the heavy lectures involving quantum mechanics!" (3.14159 265358979)
- (Alternate version of previous) "How I need a drink, alcoholic in nature, after the heavy lectures involving quantum mechanics!" (3.14159 265358979)