arl Sagan's best-selling books and his phenomenally successful 1980 public television series, Cosmos, made him the most famous scientist of his generation. Five hundred million viewers in 60 countries watched as Sagan took them on a tour of the solar system, the galaxy, and the billions and billions of stars that make up the universe. It was a record audience for a public television program. The book Sagan wrote to accompany Cosmos was on The New York Times best-seller list for 70 weeks. With Cosmos and many other books written for popular audiences, the Cornell University astronomer proved himself to be a brilliant educator and popularizer and a spellbinding storyteller. Predictably, that drew barbs from some of his colleagues. Perhaps they were wounded because they labored in relative obscurity while he became, for the public, something of a scientific oracle.

     None of that should obscure the fact, however, that Sagan made significant contributions to space science and was a visionary who helped to shape the course of American space exploration in the late 20th century. He was a passionate advocate for the search for life on other planets. He played a major role in some of the country's leading planetary exploration missions, designing experiments for the Mariner, Viking, Voyager, and Galileo space probes. He solved the mystery of the scorching temperatures on Venus by determining that they were the result of a runaway greenhouse effect. He showed that seasonal color changes on the surface of Mars were caused by windblown dust. He briefed the Apollo astronauts before their flights to the moon. Over the course of his career, he published 600 scientific papers.

     Sagan was also a remarkable writer, with a literary flair unusual for someone whose talents are concentrated in science. His 1977 book The Dragons of Eden won the Pulitzer Prize. He later became an activist, writing and lecturing extensively on the catastrophic consequences of nuclear war, and campaigning for disarmament.

     Sagan died in 1996 at the age of 62, after contracting a rare disease called myelodysplasia. It was a loss for science, and for the science-hungry public. "He was, quite simply, the best science educator in the world this century," said Yervant Terzian, chairman of Cornell's astronomy department. "Carl was a candle in the dark."

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