Pi Day. Starting in 2012, MIT has announced it will post those decisions (privately) online on Pi Day at exactly 6:28 pm, which they have called "Tau Time", to honor the rival numbers pi and tau equally. In 2015, the regular decisions were put online at 9:26 am, following that year's "pi minute", and in 2020, regular decisions were released at 1:59 pm, making the first six digits of pi. June 28 is "Two Pi Day", also known as "Tau Day". 2, also known by the Greek letter tau () is a common multiple in mathematical formulae. Some have argued that τ is the more fundamental constant, and that Tau Day should be celebrated instead. Celebrations of this date jokingly suggest eating "twice the pie". Princeton, New Jersey, hosts numerous events in a combined celebration of Pi Day and Albert Einstein's birthday, which is also March 14. Einstein lived in Princeton for more than twenty years while working at the Institute for Advanced Study. In addition to pie eating and recitation contests, there is an annual Einstein look-alike contest. Alternative dates Pi Day is most frequently observed on March 14, but related celebrations have been held on alternative dates. Pi Approximation Day is observed on July 22 (22/7 in the day/month format), since the fraction is a common approximation of , which is accurate to two decimal places and dates from Archimedes. Two Pi Day, also known as Tau Day for the mathematical constant tau, which is approximated as 6.28, is observed on June 28 (6/28 in the month/day format). Pi Approximation Day is also observed on the 10th of November since it is the 314th day of the year. See also Mole Day Sequential time Square Root Day White Day, also on March 14th List of minor secular observances Notes References External links Exploratorium's Pi Day Web Site NPR provides a "Pi Rap" audiovideo Pi Day Professor Lesser's Pi Day page 1988 establishments in California March observances July observances Observances about science Pi Recurring events established in 1988 Unofficial observances