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Sesame Street premiered on November 10, 1969 and is the longest running children's program on US television, with an amazing 39 seasons and 4,186 episodes aired. Fun fact: Sesame Street is roughly the same age as the Internet.
Honoring the event, today's Google doodle features one of the show's most recognizable characters, Big Bird.
Update: as our commenter Myatu points out, the UK version of Google today sports a different doodle, celebrating the 20th anniversary of popular animated show Wallace & Gromit!