SAN FRANCISCO (AP) _ The late astronomer and author Carl Sagan was a secret but avid marijuana smoker, crediting it with inspiring essays and scientific insight, according to Sagan’s biographer.

Using the pseudonym ``Mr. X″, Sagan wrote about his pot smoking in an essay published in the 1971 book ``Reconsidering Marijuana.″ The book’s editor, Lester Grinspoon, recently disclosed the secret to Sagan’s biographer, Keay Davidson.

Davidson, a writer for the San Francisco Examiner, revealed the marijuana use in an article published in the newspaper’s magazine Sunday. ``Carl Sagan: A Life″ is due out in October.

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``I find that today a single joint is enough to get me high ... in one movie theater recently I found I could get high just by inhaling the cannabis smoke which permeated the theater,″ wrote Sagan, who authored popular science books such as ``Cosmos,″ ``Contact,″ and ``The Dragons of Eden.″

In the essay, Sagan said marijuana inspired some of his intellectual work.

``I can remember one occasion, taking a shower with my wife while high, in which I had an idea on the origins and invalidities of racism in terms of gaussian distribution curves,″ wrote the former Cornell University professor. ``I wrote the curves in soap on the shower wall, and went to write the idea down.

Sagan also wrote that pot enhanced his experience of food, particularly potatoes, music and sex.

Grinspoon, Sagan’s closest friend for 30 years, said Sagan’s marijuana use is evidence against the notion that marijuana makes people less ambitious.

``He was certainly highly motivated to work, to contribute,″ said Grinspoon, a psychiatry professor at Harvard University.

Grinspoon is an advocate of decriminalizing marijuana.

Ann Druyan, Sagan’s former wife, is a director of the National Organization for the Reform of Marijuana Laws. The nonprofit group promotes legalization of marijuana.

Sagan died of pneumonia in 1996. He was 62.