Pi Day was first recognised 30 years ago back in 1988 by physicist Larry Shaw, according to Google. Of course, March 14 hasn't only been around for 30 years, but the date became known for a celebration of both pi the mathematical constant (which first three digits 3.14 looks like 3/14) and pies of all sorts - particularly on Google, apple pie. The Doodle represents Pi's mathematical formula-the ratio between a circle's circumference to its diameter-in pie form. Coincidentally, this is also the birthday of the legendary theoretical physicist Albert Einstein. In geometry, pie plays an important constant in finding out the area of a circle.
Mathematician Archimedes used polygons with many sides to approximate circles and determined that Pi was approximately "22/7".
The day is observed by the scientific community in the West with a slice of sweet pie. The space agency runs the "Pi in the Sky" challenge every year. Mathematicians adopted the symbol π for the expression in the 18th century: Welsh mathematics teacher William Jones is often credited with the first use of the symbol in 1706. It features math problems for calculating Martian earthquakes, helium rain on Jupiter and the rotation rate of the asteroid 'Oumuamua. In today's doodle, an image of ingredients used to bake a salted caramel apple "pie" - Google puns on the word - hints at the tradition of eating pies on this day.