Carl Sagan
Carl Sagan (1934-1996) was an American astronomer who pioneered exobiology and promoted Search for Extraterrestrial Intelligence (SETI) and science in general. He is less well known for his skepticism.
Sagan was a professor and lab director at Cornell University. He contributed to most of the unmanned space missions that explored our solar system. His idea was to add an unalterable and universal message on the spacecraft that could be understood by an extraterrestrial intelligence. The most elaborate such message he helped to develop is the Voyager Golden Record.
He was also well known as a coauthor of the paper that warned of the dangers of nuclear winter. He also perceived global warming as a growing, man-made danger and likened it to the natural development of Venus into a hot life-hostile planet through greenhouse gases. His interest in these topics was in large part motivated by his interpretation of the Drake Equation and the Fermi paradox. His opinion was that the Drake Equation suggested a large number of extraterrestial civilizations would form, but that the lack of evidence of such civilizations suggests that technological civilizations tend to destroy themselves rather quickly. This stimulated his interest in ways that humanity would destroy itself in the hopes of avoiding such destruction so that humanity could become a space-faring people.
He wrote and narrated the highly popular thirteen part PBS television series Cosmos; he wrote also books to popularise science (Broca's Brain, The Dragons of Eden, etc.) and a novel, Contact, that became a best-seller and was adapted to a film starring Jodie Foster. The film won the 1998 Hugo award. From Cosmos Sagan became associated with the catchphrase "billions and billions" which he never used in the television series.
Sagan created mixed reactions among other professional scientists. On the one hand, there was general support for his popularization of science, his efforts to increase scientific understanding among the general public, and his positions in favor of skepticism and against pseudoscience. On the other hand, there was some unease that the public would misunderstand some of the personal positions and interests that Sagan took as being part of the scientific consensus rather than his own personal views, and there was some unease, which some believe to have been motivated in part by professional jealousy, that scientific views contrary to those that Sagan took (such as on the severity of nuclear winter) were not being sufficiently presented to the public.
After a long and difficult fight with myelodysplasia, Sagan passed away at the age of 62, on Dec. 20th 1996.
See also extraterrestrial life.