Have an affinity for pi? Visit the San Francisco Exploratorium for the 25th annual Pi Day celebration, which commemorates the never-ending mathematical constant π (pi) (3.14159265359 ...). Have a happy Pi Day with pi-themed refreshments and events, while you explore the original birthplace of this worldwide holiday. Observed on March 14, Pi Day originated at the San Francisco Exploratorium, where physicist Larry Shaw organized the very first celebration back in 1988. Since that time, the holiday has spread around the world; and, in 2009, the United States House of Representatives passed a resolution naming 3/14 national pi day. These days, countless institutions commemorate the mathematical value in a variety of ways, with some throwing pies, holding formal discussions or having competitions to see which student can recite pi to the most decimal places. In fact, the celebration has become so popular, MIT now posts decisions on student application letters on 3/14. Starting at 1:00 p.m., the San Francisco Exploratorium will mark the day by holding a variety of events, including a shrine installation, educational demonstrations, a parade, Pi in the Sky-writing, refreshments and various other hands-on activities. For those who can't make the trip, the Exploratorium will be holding a separate celebration in the online virtual world, Second Life, where you can join other revelers for a virtual party on Exploratorium Island. However, if you can’t wait to attend, be sure to book a room at the Hotel Griffon, a short walk from the museum.