Science

He was an American astronomer, astrophysicist, cosmologist, author, science communicator in the space and natural sciences.

During his lifetime, he published more than 600 scientific papers and popular articles and was author, co-author, or editor of more than 20 books. In his works, he advocated skeptical inquiry and the scientific method.  He pioneered exobiology and promoted the Search for Extra-Terrestrial Intelligence (SETI). 

Sagan became world-famous for his popular science books and for the award-winning 1980 television series "Cosmos: A Personal Voyage," which he narrated and co-wrote. A book to accompany the program was also published. Sagan also wrote the novel "Contact," the basis for the 1997 film of the same name.

Carl Sagan was born in Brooklyn, New York City, to a Ukrainian Jewish family. His father, Sam Sagan, was an immigrant garment worker from Kamenets-Podolsk, Ukraine; his mother, Rachel Molly Gruber, a housewife. Carl was named in honor of Rachel's biological mother, Chaiya Clara, in Sagan's words, "the mother she never knew." Sagan graduated from Rahway High School in Rahway, New Jersey, in 1951. Sagan attended the University of Chicago earning two degrees in physics. He followed with a doctorate in Astronomy in 1960 and taught at Harvard University until 1968, when he moved to Cornell University. Sagan became a teacher and director at Cornell in 1971. He helped many unmanned spacecraft to explore outer space. He thought of the idea of putting a message on spacecraft which could be understood by any life from another planet that might find it. The first message sent into space was a large gold-plated label on the space probe Pioneer 10. He continued to make the messages better. The last message he helped with was the Voyager Golden Record that was sent out with the Voyager space probes. He was well known as a writer who warned of the dangers of nuclear winter. He helped people learn about the atmosphere of Venus, seasonal changes on Mars, and Saturn's moon Titan. He showed that the atmosphere of Venus is very hot and dense.

Solar System Scope: An Interactive View

Sagan also said that global warming was a growing, man-made danger like the natural development of Venus into a hot and dangerous planet with greenhouse gases. He suggested that the seasonal changes on Mars were due to dust storms and was among the first  to guess that Titan and Jupiter's moon Europa might have oceans or lakes, which means that life could be there. Europa's underground ocean was later confirmed by the spacecraft Galileo. Sagan thought the search for life on other planets was a good idea. He said scientists should listen with large radio telescopes for signals from other planets. He thought sending probes to other planets was a good idea. Sagan was editor of Icarus (a magazine about space exploration) for 12 years. He helped start the Planetary Society and was a member of the SETI Institute Board of Trustees.

Sagan believed that the Drake equation (equation used to estimate the number of detectable extraterrestrial civilizations in the Milky Way Galaxy) and suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations highlighted by the Fermi paradox (the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for it or contact with such civilizations) suggests technological civilizations tend to destroy themselves rather quickly.

This stimulated his interest in identifying and publicizing ways that humanity could destroy itself, with the hope of avoiding such a cataclysm and eventually becoming a spacefaring species. Sagan's deep concern regarding the potential destruction of human civilization in a nuclear holocaust was conveyed in a memorable cinematic sequence in the final episode of Cosmos, called "Who Speaks for Earth?"

Sagan had already resigned from the Air Force Scientific Advisory Board and voluntarily surrendered his top secret clearance in protest over the Vietnam War.  Following his marriage to his third wife (novelist Ann Druyan) in June 1981, Sagan became more politically active — particularly in opposing escalation of the nuclear arms race under President Ronald Reagan. In March 1983, Reagan announced the Strategic Defense Initiative — a multi-billion dollar project to develop a comprehensive defense against attack by nuclear missiles, which was quickly dubbed the "Star Wars" program. Sagan spoke out against the project, arguing that it was technically impossible to develop a system with the level of perfection required, and far more expensive to build than for an enemy to defeat through decoys and other means — and that its construction would seriously destabilize the nuclear balance between the United States and the Soviet Union, making further progress toward nuclear disarmament impossible. When Soviet leader Mikhail Gorbachev declared a unilateral moratorium on the testing of nuclear weapons, which would begin on August 6, 1985 — the 40th anniversary of the atomic bombing of Hiroshima — the Reagan administration dismissed the dramatic move as nothing more than propaganda, and refused to follow suit. In response, American anti-nuclear and peace activists staged a series of protest actions at the Nevada Test Site, beginning on Easter Sunday in 1986 and continuing through 1987. Hundreds of people were arrested, including Sagan, who was arrested on two separate occasions as he climbed over a chain-link fence at the test site.

Sagan wrote frequently about religion and the relationship between religion and science, expressing his skepticism about the conventional conceptualization of God as a sapient being.  He said: "Some people think God is an outsized, light-skinned male with a long white beard, sitting on a throne somewhere up there in the sky, busily tallying the fall of every sparrow. Others — for example Baruch Spinoza and Albert Einstein — considered God to be essentially the sum total of the physical laws which describe the universe. I do not know of any compelling evidence for anthropomorphic patriarchs controlling human destiny from some hidden celestial vantage point, but it would be madness to deny the existence of physical laws.  In another description of his view of God, Sagan emphatically writes: "The idea that God is an oversized white male with a flowing beard who sits in the sky and tallies the fall of every sparrow is ludicrous. But if by God one means the set of physical laws that govern the universe, then clearly there is such a God. This God is emotionally unsatisfying... it does not make much sense to pray to the law of gravity."  Despite his criticism of religion, Sagan denied that he was an atheist, saying "An atheist has to know a lot more than I know. An atheist is someone who knows there is no god. By some definitions atheism is very stupid." In reply to a question in 1996 about his religious beliefs, Sagan answered, "I'm agnostic." Sagan's view have been interpreted as a form of pantheism comparable to Einstein's belief in Spinoza's God.  Sagan maintained that the idea of a creator of the universe was difficult to prove or disprove and that the only conceivable scientific discovery that could challenge it would be an infinitely old universe.