The earliest known official or large-scale celebration of Pi Day was organized by Larry Shaw in 1988 at the San Francisco Exploratorium, where Shaw worked as a physicist, with staff and public marching around one of its circular spaces, then consuming fruit pies. The Exploratorium continues to hold Pi Day celebrations.
Pi Day has been observed in many ways, including eating pie, throwing pies and discussing the significance of the numberπ, due to a pun based on the words “pi” and “pie” being homophones in English (pronunciation: /paɪ/), as well as pies tending to be round, and thus related to π.
Massachusetts Institute of Technology has often mailed its application decision letters to prospective students for delivery on 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 moment”.
The town of 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.