If you accept the American style of writing a date (month first, then the day) then today you'll be celebrating Day - when the date 3.14 matches the first few digits of . But this year it's a bit more special because including the last two digits of the year matches the first five digits 3.1415.  And then even more special at 26 minutes and 53 seconds past 9 o'clock (am or pm, I suppose) when the date and time will match the first 10 digits of .  Here are a couple of nice articles from today's newspapers about Day - one of them by Alex Bellos the author of Alex's Adventures in Numberland and Alex Through the Looking Glass: How Life Reflects Numbers and Numbers Reflect Life, two very good books about mathematics.

Pi Day 2015: a sweet treat for maths fans (The Guardian), by Alex Bellos

Don’t Expect Math to Make Sense: On Pi Day, Celebrate Math’s Enigmas (New York Times) by Manil Suri (a mathematics professor at the University of Maryland)

From reading the article by Alex Bellos I learned that the last Day that was "better" than today was March 14, 1592.  On that day at 53 minutes and 58 seconds past 6 o'clock the date and time 3.14.1592, 6:53:58 matched the first 12 digits of .  Ask your students what famous mathematicians and scientists were alive at that time.  Of course, there were no Americans around to write the date in a way which allows us to celebrate a very special number.