<human>:  When did the astronomer Carl Sagan die?
<bot>: Carl Sagan died on December 20, 1996, at the age of 62. He was a famous American astronomer, popularizer of science, and science fiction writer. He was a professor of astronomy at Cornell University, and a popularizer of science, especially popularizing science through his books, television series, and lectures. He was also the host of the television series Cosmos: A Personal Voyage, which is one of the highest rated PBS television series in history.