March 13 was Friday, the thirteenth. Interestingly, this year, February 13, too, was a Friday. March 14 was Pi Day! Why? Because, the date matched the approximation of pi, a mathematical constant.
Pi, the ratio of a circle's circumference to its diameter, is approximated as 3.1415926. So, March 14, '15 became 3.1415. Some went further to celebrate the hour and minutes—March 14, '15, 9:26pm.
In the US, public institutions found innovative ways to celebrate the day. Apparently, Pi Day was first celebrated 27 years ago by the Exploratorium museum in Los Angeles, California. So, this year, entry into the museum was free on that day. Chicago's Museum of Science and Industry offered a free slice of pie or pizza to the first 314 visitors; those who missed the free bites could buy it for—$3.14.
Residents of Denver, Colorado, were encouraged to run a 3.14-mile (5.05km) course around the city's beautiful Washington Park. The park itself is only 2.35 miles (3.78km) around, so runners had to run the 'extra mile' to fully honour the Pi gods.
The National Museum of Mathematics invited New Yorkers to Madison Square Park (not Madison Square Garden, where Prime Minister Narendra Modi spoke) for a glow-in-the-dark demo on the meaning of pi, at 9:26pm!
While mathematicians celebrated Pi Day for pi, physicists did it for another reason—Albert Einstein was born on March 14. India, too, must find ways to celebrate the Pi Day, no? Got an idea? Drop a mail to firstname.lastname@example.org