As to why a Google Doodle is celebrating the 30th anniversary of Pi, it is because the mathematical constant touches infinity in numerous ways. This year marks the 30th anniversary of Pi Day, observed annually on March 14 (3.14).
In 1988, physicist Larry Shaw first found the constant Pi which is often the most used constant in many various fields of mathematics, especially in geometry. Incidentally, in 2009, the United States House of Representatives had voted in favour of designating today as Pi day. Pi, which is quite popular among students around the world as it represents the ratio of the circumference of any circle to its diameter. He went on to create a caramel apple pie which according to him, it is one of the most classic forms of apple pies, therefore symbolising the mathematical constant pi which like an apple pie remains a constant favourite among the people. The Pilish dialect was invented, in which the numbers of letters in successive words matched the digits of pi. The website also has a record of the problems from previous years.
March 14 is celebrated as Pi Day when the date lines up in the numbers of the famous constant.
Pi Day was first celebrated by physicist Larry Shaw at the Exploratorium in San Francisco nearly 30 years ago and incidentally in 2009, the United States House of Representatives voted in favour of designating 3/14 as Pi Day. This involves the calculation of Martian earthquakes, the helium rain on Jupiter and the rotation rate of asteroids and even the solar eclipse.