Pi Day Leave a comment Happy Pi Day! Pi Day celebrates the mathematical constant pi. (The date was chosen because the first three digits of pi are 3.14.) It is also Albert Einstein’s birthday, and Stephen Hawking died on Pi Day in 2018. Pi Day through time: From Linux to Einstein to Steph CurryMarch 14 isn’t just Pi Day. It also has a surprising history of famous births, the death of physicist Stephen Hawking and a milestone for a daring dirigible.