Today is Google's 13 year old birthday and to celebrate, Google has a special birthday logo with a cake, birthday hats and more! It reminds me of pictures of my childhood birthday parties in the 1980s.
In any event, 13 is an important birthday - it is technically a Bar Mitzvah! :)
That being said, there has been controversy over when Google was born. Was it September 27th or September 14th. Google is now going with the 27th date.
For the past year birthday logos, see the 12th birthday, 11th birthday, the 10th also, 9th, 8th, the 7th and 6th. The 7th and 6th were celebrated on different days than the later ones, due to there being confusion on when Google's real birthday is.
Happy birthday Google!