Carl Edward Sagan (//; November 9, 1934 – December 20, 1996) was an American astronomer, cosmologist, astrophysicist, astrobiologist, author, science popularizer, and science communicator in astronomy and other natural sciences. His contributions were central to the discovery of the high surface temperatures of Venus. However, he is best known for his contributions to the scientific research of extraterrestrial life, including experimental demonstration of the production of amino acids from basic chemicals by radiation. Sagan assembled the first physical messages that were sent into space: the Pioneer plaque and the Voyager Golden Record, universal messages that could potentially be understood by any extraterrestrial intelligence that might find them.
He published more than 600 scientific papers and articles and was author, co-author or editor of more than 20 books. Sagan is known for many of his popular science books, such as The Dragons of Eden, Broca's Brain and Pale Blue Dot, and for the award-winning 1980 television series Cosmos: A Personal Voyage, which he narrated and co-wrote. The most widely watched series in the history of American public television, Cosmos has been seen by at least 500 million people across 60 different countries. The book Cosmos was published to accompany the series. He also wrote the science fiction novel Contact, the basis for a 1997 film of the same name.
Sagan always advocated scientific skeptical inquiry and the scientific method, pioneered exobiology and promoted the Search for Extra-Terrestrial Intelligence (SETI). He spent most of his career as a professor of astronomy at Cornell University, where he directed the Laboratory for Planetary Studies. Sagan and his works received numerous awards and honors, including the NASA Distinguished Public Service Medal, the National Academy of Sciences Public Welfare Medal, the Pulitzer Prize for General Non-Fiction for his book The Dragons of Eden, and, regarding Cosmos: A Personal Voyage, two Emmy Awards, the Peabody Award and the Hugo Award. He married three times and had five children. After suffering from myelodysplasia, Sagan died of pneumonia at the age of 62 on December 20, 1996.
- 1 Early life
- 2 Education and scientific career
- 3 Scientific achievements
- 4 Scientific and critical thinking advocacy
- 5 Social concerns
- 6 Personal life and beliefs
- 7 Sagan and UFOs
- 8 Death
- 9 Posthumous recognition
- 10 Awards and honors
- 11 Publications
- 12 See also
- 13 References
- 14 Further reading
- 15 External links
Carl Sagan was born in Brooklyn, New York. His father, Samuel Sagan, was an immigrant garment worker from Kamianets-Podilskyi, then Russian Empire, in today's Ukraine. His mother, Rachel Molly Gruber, was a housewife from New York. 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.
He had a sister, Carol, and the family lived in a modest apartment near the Atlantic Ocean, in Bensonhurst, a Brooklyn neighborhood. According to Sagan, they were Reform Jews, the most liberal of North American Judaism's four main groups. Both Sagan and his sister agreed that their father was not especially religious, but that their mother "definitely believed in God, and was active in the temple ... and served only kosher meat".:12 During the depths of the Depression, his father worked as a theater usher.
According to biographer Keay Davidson, Sagan's "inner war" was a result of his close relationship with both of his parents, who were in many ways "opposites". Sagan traced his later analytical urges to his mother, a woman who had known "extreme poverty as a child" in New York City during World War I and the 1920s.:2 As a young woman she had held her own intellectual ambitions, but they were frustrated by social restrictions: her poverty, her status as a woman and a wife, and her Jewish ethnicity. Davidson notes that she therefore "worshiped her only son, Carl. He would fulfill her unfulfilled dreams".:2
However, his "sense of wonder" came from his father, who was a "quiet and soft-hearted escapee from the Czar". In his free time he gave apples to the poor or helped soothe labor-management tensions within New York's "tumultuous" garment industry.:2 Although he was "awed" by Carl's "brilliance, his boyish chatter about stars and dinosaurs", he took his son's inquisitiveness in stride and saw it as part of his growing up.:2 In his later years as a writer and scientist, Sagan would often draw on his childhood memories to illustrate scientific points, as he did in his book, Shadows of Forgotten Ancestors.:9 Sagan describes his parents' influence on his later thinking:
- My parents were not scientists. They knew almost nothing about science. But in introducing me simultaneously to skepticism and to wonder, they taught me the two uneasily cohabiting modes of thought that are central to the scientific method.
1939 World's Fair
Sagan recalls that one of his most defining moments was when his parents took him to the 1939 New York World's Fair when he was four years old. The exhibits became a turning point in his life. He later recalled the moving map of the America of Tomorrow exhibit: "It showed beautiful highways and cloverleaves and little General Motors cars all carrying people to skyscrapers, buildings with lovely spires, flying buttresses—and it looked great!":14 At other exhibits, he remembered how a flashlight that shone on a photoelectric cell created a crackling sound, and how the sound from a tuning fork became a wave on an oscilloscope. He also witnessed the future media technology that would replace radio: television. Sagan wrote:
- Plainly, the world held wonders of a kind I had never guessed. How could a tone become a picture and light become a noise?:14
He also saw one of the Fair's most publicized events, the burial of a time capsule at Flushing Meadows, which contained mementos of the 1930s to be recovered by Earth's descendants in a future millennium. "The time capsule thrilled Carl," writes Davidson. As an adult, Sagan and his colleagues would create similar time capsules—ones that would be sent out into the galaxy; these were the Pioneer plaque and the Voyager Golden Record records, all of which were spinoffs of Sagan's memories of the World's Fair.:15
World War II
During World War II Sagan's family worried about the fate of their European relatives. Sagan, however, was generally unaware of the details of the ongoing war. He writes, "Sure, we had relatives who were caught up in the Holocaust. Hitler was not a popular fellow in our household ... But on the other hand, I was fairly insulated from the horrors of the war." His sister, Carol, said that their mother "above all wanted to protect Carl ... She had an extraordinarily difficult time dealing with World War II and the Holocaust".:15 Sagan's book, The Demon-Haunted World (1996), included his memories of this conflicted period, when his family dealt with the realities of the war in Europe but tried to prevent it from undermining his optimistic spirit.
Inquisitiveness about nature
Soon after entering elementary school he began to express a strong inquisitiveness about nature. Sagan recalled taking his first trips to the public library alone, at the age of five, when his mother got him a library card. He wanted to learn what stars were, since none of his friends or their parents could give him a clear answer:
- I went to the librarian and asked for a book about stars ... And the answer was stunning. It was that the Sun was a star but really close. The stars were suns, but so far away they were just little points of light ... The scale of the universe suddenly opened up to me. It was a kind of religious experience. There was a magnificence to it, a grandeur, a scale which has never left me. Never ever left me.:18
At about age six or seven, he and a close friend took trips to the American Museum of Natural History in New York City. While there, they went to the Hayden Planetarium and walked around the museum's exhibits of space objects, such as meteorites, and displays of dinosaurs and animals in natural settings. Sagan writes about those visits:
- I was transfixed by the dioramas—lifelike representations of animals and their habitats all over the world. Penguins on the dimly lit Antarctic ice; ... a family of gorillas, the male beating his chest, ... an American grizzly bear standing on his hind legs, ten or twelve feet tall, and staring me right in the eye.:18
His parents helped nurture his growing interest in science by buying him chemistry sets and reading materials. His interest in space, however, was his primary focus, especially after reading science fiction stories by writers such as H. G. Wells and Edgar Rice Burroughs, which stirred his imagination about life on other planets such as Mars. According to biographer Ray Spangenburg, these early years as Sagan tried to understand the mysteries of the planets became a "driving force in his life, a continual spark to his intellect, and a quest that would never be forgotten."
In 1947 he discovered Astounding Science Fiction magazine, which introduced him to more hard science fiction speculations than those in Burroughs's novels. That same year inaugurated the "flying saucer" mass hysteria with the young Carl suspecting the "discs" might be alien spaceships.
Education and scientific career
He attended the University of Chicago, where he participated in the Ryerson Astronomical Society, received a bachelor of arts in self-proclaimed "nothing" with general and special honors in 1954, a bachelor of science in physics in 1955, and a master of science in physics in 1956 before earning a PhD in 1960 with the dissertation "Physical Studies of Planets" submitted to the Department of Astronomy and Astrophysics. The title of Sagan's thesis reflects his shared interests with Gerard Kuiper, his dissertation director, who throughout the 1950s had been president of the International Astronomical Union's commission on "Physical Studies of Planets and Satellites".
During his time as an honors program undergraduate, Sagan worked in the laboratory of the geneticist H. J. Muller and wrote a thesis on the origins of life with physical chemist H. C. Urey. He used the summer months of his graduate studies to work with planetary scientist Gerard Kuiper, physicist George Gamow, and chemist Melvin Calvin. From 1960 to 1962 Sagan was a Miller Fellow at the University of California, Berkeley. From 1962 to 1968, he worked at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts. At the same time, he worked with geneticist Joshua Lederberg.
Sagan lectured and did research at Harvard University until 1968, when he moved to Cornell University in Ithaca, New York, after being denied tenure at Harvard. It has been suggested that Sagan was denied tenure in part because of his publicized scientific advocacy, which some scientists perceived as being self-promotion; his denial was at least partly due to Harold Urey sending an anti-Sagan letter to the tenure committee. He became a full professor at Cornell in 1971, and directed the Laboratory for Planetary Studies there. From 1972 to 1981, Sagan was associate director of the Center for Radiophysics and Space Research (CRSR) at Cornell.
Sagan was associated with the U.S. space program from its inception. From the 1950s onward, he worked as an advisor to NASA, where one of his duties included briefing the Apollo astronauts before their flights to the Moon. Sagan contributed to many of the robotic spacecraft missions that explored the Solar System, arranging experiments on many of the expeditions. He conceived the idea of adding an unalterable and universal message on spacecraft destined to leave the Solar System that could potentially be understood by any extraterrestrial intelligence that might find it. Sagan assembled the first physical message that was sent into space: a gold-anodized plaque, attached to the space probe Pioneer 10, launched in 1972. Pioneer 11, also carrying another copy of the plaque, was launched the following year. He continued to refine his designs; the most elaborate message he helped to develop and assemble was the Voyager Golden Record that was sent out with the Voyager space probes in 1977. Sagan often challenged the decisions to fund the Space Shuttle and the International Space Station at the expense of further robotic missions.
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Former student David Morrison describes Sagan as "an 'idea person' and a master of intuitive physical arguments and 'back of the envelope' calculations," and Gerard Kuiper said that "Some persons work best in specializing on a major program in the laboratory; others are best in liaison between sciences. Dr. Sagan belongs in the latter group."
Sagan's contributions were central to the discovery of the high surface temperatures of the planet Venus. In the early 1960s no one knew for certain the basic conditions of that planet's surface, and Sagan listed the possibilities in a report later depicted for popularization in a Time–Life book, Planets. His own view was that Venus was dry and very hot as opposed to the balmy paradise others had imagined. He had investigated radio emissions from Venus and concluded that there was a surface temperature of 500 °C (900 °F). As a visiting scientist to NASA's Jet Propulsion Laboratory, he contributed to the first Mariner missions to Venus, working on the design and management of the project. Mariner 2 confirmed his conclusions on the surface conditions of Venus in 1962.
Sagan was among[clarification needed] the first to hypothesize that Saturn's moon Titan might possess oceans of liquid compounds on its surface and that Jupiter's moon Europa might possess subsurface oceans of water. This would make Europa potentially habitable. Europa's subsurface ocean of water was later indirectly confirmed by the spacecraft Galileo. The mystery of Titan's reddish haze was also solved with Sagan's help. The reddish haze was revealed to be due to complex organic molecules constantly raining down onto Titan's surface.
He further contributed insights regarding the atmospheres of Venus and Jupiter as well as seasonal changes on Mars. 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 a kind of runaway greenhouse effect. Sagan and his Cornell colleague Edwin Ernest Salpeter speculated about life in Jupiter's clouds, given the planet's dense atmospheric composition rich in organic molecules. He studied the observed color variations on Mars' surface and concluded that they were not seasonal or vegetational changes as most believed[clarification needed] but shifts in surface dust caused by windstorms.
Sagan is best known, however, for his research on the possibilities of extraterrestrial life, including experimental demonstration of the production of amino acids from basic chemicals by radiation.
He is also the 1994 recipient of the Public Welfare Medal, the highest award of the National Academy of Sciences for "distinguished contributions in the application of science to the public welfare". He was denied membership in the Academy, reportedly because his media activities made him unpopular with many other scientists.
Scientific and critical thinking advocacy
Sagan's ability to convey his ideas allowed many people to understand the cosmos better—simultaneously emphasizing the value and worthiness of the human race, and the relative insignificance of the Earth in comparison to the Universe. He delivered the 1977 series of Royal Institution Christmas Lectures in London. He hosted and, with Ann Druyan, co-wrote and co-produced the highly popular thirteen-part Public Broadcasting Service (PBS) television series Cosmos: A Personal Voyage.
Cosmos covered a wide range of scientific subjects including the origin of life and a perspective of our place in the Universe. The series was first broadcast by PBS in 1980, winning an Emmy and a Peabody Award. It has been broadcast in more than 60 countries and seen by over 500 million people, making it the most widely watched PBS program in history. In addition, Time magazine ran a cover story about Sagan soon after the show broadcast, referring to him as "creator, chief writer and host-narrator of the new public television series Cosmos, [and] takes the controls of his fantasy spaceship". However, Sagan was criticized for putting too much attention into the series, with several of his classes at Cornell being cancelled and complaints from his colleagues.
Sagan was a proponent of the search for extraterrestrial life. He urged the scientific community to listen with radio telescopes for signals from potential intelligent extraterrestrial life-forms. Sagan was so persuasive that by 1982 he was able to get a petition advocating SETI published in the journal Science and signed by 70 scientists, including seven Nobel Prize winners. This was a tremendous increase in the respectability of this controversial field. Sagan also helped Frank Drake write the Arecibo message, a radio message beamed into space from the Arecibo radio telescope on November 16, 1974, aimed at informing potential extraterrestrials about Earth.
Sagan was chief technology officer of the professional planetary research journal Icarus for twelve years. He co-founded The Planetary Society, the largest space-interest group in the world, with over 100,000 members in more than 149 countries, and was a member of the SETI Institute Board of Trustees. Sagan served as Chairman of the Division for Planetary Science of the American Astronomical Society, as President of the Planetology Section of the American Geophysical Union, and as Chairman of the Astronomy Section of the American Association for the Advancement of Science (AAAS).
At the height of the Cold War, Sagan became involved in public awareness efforts for the effects of nuclear war when a 1982 mathematical climate model, titled "Twilight at Noon" suggested that a substantial nuclear exchange could trigger a nuclear twilight and upset the delicate balance of life on Earth by cooling the surface. In 1983 he was one of five authors—the "S"—in the follow-up "TTAPS" report, as the research paper came to be known, which contained the term "nuclear winter" for the first time, a term coined by his colleague Richard P. Turco. In 1984 he co-authored the book The Cold and the Dark: The World after Nuclear War and in 1990 he co-authored the book A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race, which explains the nuclear winter hypothesis and with that advocates nuclear disarmament.
Sagan also wrote books to popularize science, such as Cosmos, which reflected and expanded upon some of the themes of A Personal Voyage and became the best-selling science book ever published in English; The Dragons of Eden: Speculations on the Evolution of Human Intelligence, which won a Pulitzer Prize; and Broca's Brain: Reflections on the Romance of Science. Sagan also wrote the best-selling science fiction novel Contact in 1985, based on a film treatment he wrote with his wife in 1979, but he did not live to see the book's 1997 motion picture adaptation, which starred Jodie Foster and won the 1998 Hugo Award for Best Dramatic Presentation.
He wrote a sequel to Cosmos, Pale Blue Dot: A Vision of the Human Future in Space, which was selected as a notable book of 1995 by The New York Times. He appeared on PBS' Charlie Rose program in January 1995. Sagan also wrote the introduction for Stephen Hawking's bestseller, A Brief History of Time. Sagan was also known for his popularization of science, his efforts to increase scientific understanding among the general public, and his positions in favor of scientific skepticism and against pseudoscience, such as his debunking of the Betty and Barney Hill abduction. To mark the tenth anniversary of Sagan's death, David Morrison, a former student of Sagan's, recalled "Sagan's immense contributions to planetary research, the public understanding of science, and the skeptical movement" in Skeptical Inquirer.
Following Saddam Hussein's threats to light Kuwait's oil wells on fire in response to any physical challenge to Iraqi control of the oil assets, Sagan and his nuclear winter/"TTAPS" colleagues warned in January 1991 in the Baltimore Sun and Wilmington Morning Star newspapers that if the fires were left to burn over a period of several months, enough smoke from the 600 or so 1991 Kuwaiti oil fires "might get so high as to disrupt agriculture in much of South Asia ..." and that this possibility should "affect the war plans"; these claims were also the subject of a televised debate between Sagan and physicist Fred Singer on 22 January, aired on the ABC News program Nightline.
In the televised debate, Sagan argued that the effects of the smoke would be similar to the effects of a nuclear winter, with Singer arguing to the contrary. After the debate, the fires burnt for many months before extinguishing efforts were complete, the results of the smoke did not produce continental sized cooling. Sagan later conceded in The Demon-Haunted World that their prediction did not turn out to be correct: "it was pitch black at noon and temperatures dropped 4°–6 °C over the Persian Gulf, but not much smoke reached stratospheric altitudes and Asia was spared". A 2007 study noted that modern computer models have been applied to the Kuwait oil fires, finding that individual smoke plumes are not able to loft smoke into the stratosphere, but that smoke from a particular type of large fire, known as a firestorm, which frequently manifest in some dense forest fires and which are capable of occurring in modern cities following a nuclear strike, would loft significant amounts of smoke into the stratosphere.
In his later years Sagan advocated the creation of an organized search for near-Earth objects (NEO) that might impact the Earth. When others suggested creating large nuclear bombs that could be used to alter the orbit of a NEO that was predicted to hit the Earth, Sagan proposed the Deflection Dilemma: If we create the ability to deflect an asteroid away from the Earth, then we may also create the ability to deflect an asteroid towards the Earth—providing an evil power with a true doomsday bomb. His interest in the use of nuclear weapons in space grew out of his work in 1958 for the Armour Research Foundation's Project A119, concerning the possibility of detonating a nuclear device on the Lunar surface.
Sagan was a critic of Plato. Sagan said of Plato: "Science and mathematics were to be removed from the hands of the merchants and the artisans. This tendency found its most effective advocate in a follower of Pythagoras named Plato." and "He (Plato) believed that ideas were far more real than the natural world. He advised the astronomers not to waste their time observing the stars and planets. It was better, he believed, just to think about them. Plato expressed hostility to observation and experiment. He taught contempt for the real world and disdain for the practical application of scientific knowledge. Plato's followers succeeded in extinguishing the light of science and experiment that had been kindled by Democritus and the other Ionians."
Speaking about his activities in popularizing science, Sagan said that there were at least two reasons for scientists to explain what science is about. Naked self-interest was one because much of the funding for science came from the public, and the public had a right to know how their money was being spent. If scientists increased public excitement about science, there was a good chance of having more public supporters. The other reason was the excitement of communicating one's own excitement about science to others.
"Billions and billions"
From Cosmos and his frequent appearances on The Tonight Show Starring Johnny Carson, Sagan became associated with the catchphrase "billions and billions". Sagan said that he never actually used the phrase in the Cosmos series. The closest that he ever came was in the book Cosmos, where he talked of "billions upon billions":
A galaxy is composed of gas and dust and stars—billions upon billions of stars.
(Richard Feynman, a precursor to Sagan, is observed to use the phrase "billions and billions" many times in his "red books".) However, Sagan's frequent use of the word billions, and distinctive delivery emphasizing the "b" (which he did intentionally, in place of more cumbersome alternatives such as "billions with a 'b'", in order to distinguish the word from "millions"), made him a favorite target of comic performers, including Johnny Carson, Gary Kroeger, Mike Myers, Bronson Pinchot, Penn Jillette, Harry Shearer, and others. Frank Zappa satirized the line in the song "Be in My Video", noting as well "atomic light". Sagan took this all in good humor, and his final book was entitled Billions and Billions, which opened with a tongue-in-cheek discussion of this catchphrase, observing that Carson was an amateur astronomer and that Carson's comic caricature often included real science.
He is also known for expressing wonderment at the vastness of space and time, as in his phrase "The total number of stars in the Universe is larger than all the grains of sand on all the beaches of the planet Earth."
As a humorous tribute to Sagan and his association with the catchphrase "billions and billions", a sagan has been defined as a unit of measurement equivalent to a very large number of anything.
Sagan believed that the Drake equation, on substitution of reasonable estimates, suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations highlighted by the Fermi paradox suggests technological civilizations tend to self-destruct. 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[date missing] from the Air Force Scientific Advisory Board's UFO investigating Condon Committee 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 such a system than it would be for an enemy to defeat it 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, US 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 in the "Nevada Desert Experience" group were arrested, including Sagan, who was arrested on two separate occasions as he climbed over a chain-link fence at the test site during the underground Operation Charioteer and United States's Musketeer nuclear test series of detonations.
Sagan was also a vocal advocate of the controversial notion of "Testosterone poisoning", arguing in 1992 that human males could become gripped by an "usually severe [case of] testosterone poisoning" and this could compel them to become genocidal. In his review of Moondance magazine writer; Daniela Gioseffi's 1990 book Women on War, he argues that females are the only "half" of humanity "untainted by testosterone poisoning". One chapter of his 1993 book, Shadows of Forgotten Ancestors is dedicated to testosterone and its alleged poisonous effects.
Personal life and beliefs
Sagan was married three times. In 1957, he married biologist Lynn Margulis, mother of Dorion Sagan and Jeremy Sagan. After Sagan and Margulis divorced, he married artist Linda Salzman in 1968, mother of Nick Sagan. During these marriages, Sagan focused heavily on his career, a factor which may have contributed to Sagan's first divorce. In 1981, Sagan married author Ann Druyan, mother of Alexandra Rachel (Sasha) Sagan and Samuel Democritus Sagan. Sagan and Druyan remained married until his death in 1996.
Isaac Asimov described Sagan as one of only two people he ever met whose intellect surpassed his own. The other, he claimed, was the computer scientist and artificial intelligence expert Marvin Minsky.
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. For example:
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 on the concept 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.
On atheism, Sagan commented in 1981:
An atheist is someone who is certain that God does not exist, someone who has compelling evidence against the existence of God. I know of no such compelling evidence. Because God can be relegated to remote times and places and to ultimate causes, we would have to know a great deal more about the universe than we do now to be sure that no such God exists. To be certain of the existence of God and to be certain of the nonexistence of God seem to me to be the confident extremes in a subject so riddled with doubt and uncertainty as to inspire very little confidence indeed.
Sagan also commented on Christianity, stating "My long-time view about Christianity is that it represents an amalgam of two seemingly immiscible parts, the religion of Jesus and the religion of Paul. Thomas Jefferson attempted to excise the Pauline parts of the New Testament. There wasn't much left when he was done, but it was an inspiring document."
Regarding the relationship between spirituality and science, Sagan stated: "Science is not only compatible with spirituality; it is a profound source of spirituality. When we recognize our place in an immensity of light-years and in the passage of ages, when we grasp the intricacy, beauty, and subtlety of life, then that soaring feeling, that sense of elation and humility combined, is surely spiritual."
An environmental appeal, "Preserving and Cherishing the Earth", signed by Sagan with other noted scientists in January 1990, stated that "The historical record makes clear that religious teaching, example, and leadership are powerfully able to influence personal conduct and commitment... Thus, there is a vital role for religion and science."
In reply to a question in 1996 about his religious beliefs, Sagan answered, "I'm agnostic." Sagan maintained that the idea of a creator God 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. Sagan's views on religion have been interpreted as a form of pantheism comparable to Einstein's belief in Spinoza's God. His son, Dorion Sagan said, "My father believed in the God of Spinoza and Einstein, God not behind nature but as nature, equivalent to it." His last wife, Ann Druyan, stated:
When my husband died, because he was so famous and known for not being a believer, many people would come up to me—it still sometimes happens—and ask me if Carl changed at the end and converted to a belief in an afterlife. They also frequently ask me if I think I will see him again. Carl faced his death with unflagging courage and never sought refuge in illusions. The tragedy was that we knew we would never see each other again. I don't ever expect to be reunited with Carl.
In 2006, Ann Druyan edited Sagan's 1985 Glasgow Gifford Lectures in Natural Theology into a book, The Varieties of Scientific Experience: A Personal View of the Search for God, in which he elaborates on his views of divinity in the natural world.
Sagan is also widely regarded as a freethinker or skeptic; one of his most famous quotations, in Cosmos, was, "Extraordinary claims require extraordinary evidence" (called the "Sagan Standard" by some). This was based on a nearly identical statement by fellow founder of the Committee for the Scientific Investigation of Claims of the Paranormal, Marcello Truzzi, "An extraordinary claim requires extraordinary proof." This idea had been earlier aphorized in Théodore Flournoy's work From India to the Planet Mars (1899) from a longer quote by Pierre-Simon Laplace (1749–1827), a French mathematician and astronomer, as the Principle of Laplace: "The weight of the evidence should be proportioned to the strangeness of the facts."
Late in his life, Sagan's books elaborated on his skeptical, naturalistic view of the world. In The Demon-Haunted World, he presented tools for testing arguments and detecting fallacious or fraudulent ones, essentially advocating wide use of critical thinking and the scientific method. The compilation Billions and Billions: Thoughts on Life and Death at the Brink of the Millennium, published in 1997 after Sagan's death, contains essays written by Sagan, such as his views on abortion, and his widow Ann Druyan's account of his death as a skeptic, agnostic, and freethinker.
Sagan warned against humans' tendency towards anthropocentrism. He was the faculty adviser for the Cornell Students for the Ethical Treatment of Animals. In the Cosmos chapter "Blues For a Red Planet", Sagan wrote, "If there is life on Mars, I believe we should do nothing with Mars. Mars then belongs to the Martians, even if the Martians are only microbes."
Sagan was a user and advocate of marijuana. Under the pseudonym "Mr. X", he contributed an essay about smoking cannabis to the 1971 book Marihuana Reconsidered. The essay explained that marijuana use had helped to inspire some of Sagan's works and enhance sensual and intellectual experiences. After Sagan's death, his friend Lester Grinspoon disclosed this information to Sagan's biographer, Keay Davidson. The publishing of the biography, Carl Sagan: A Life, in 1999 brought media attention to this aspect of Sagan's life. Not long after his death, widow Ann Druyan had gone on to preside over the board of directors of the National Organization for the Reform of Marijuana Laws (NORML), a non-profit organization dedicated to reforming cannabis laws.
In 1994, engineers at Apple Computer code-named the Power Macintosh 7100 "Carl Sagan" in the hope that Apple would make "billions and billions" with the sale of the PowerMac 7100. The name was only used internally, but Sagan was concerned that it would become a product endorsement and sent Apple a cease-and-desist letter. Apple complied, but engineers retaliated by changing the internal codename to "BHA" for “Butt-Head Astronomer”. Sagan then sued Apple for libel, a form of defamation, in federal court. The court granted Apple's motion to dismiss Sagan's claims and opined in dicta that a reader aware of the context would understand Apple was "clearly attempting to retaliate in a humorous and satirical way", and that “It strains reason to conclude that Defendant was attempting to criticize Plaintiff's reputation or competency as an astronomer. One does not seriously attack the expertise of a scientist using the undefined phrase ‘butt-head’.” Sagan then sued for Apple's original use of his name and likeness, but again lost. Sagan appealed the ruling. In November 1995, an out-of-court settlement was reached and Apple's office of trademarks and patents released a conciliatory statement that “Apple has always had great respect for Dr. Sagan. It was never Apple's intention to cause Dr. Sagan or his family any embarrassment or concern.” Apple's third and final code name for the project was "LAW", short for "Lawyers are Wimps".
Sagan and UFOs
Sagan's interest in UFO reports prompted him on August 3, 1952, to write a letter to U.S. Secretary of State Dean Acheson to ask how the United States would respond if flying saucers turned out to be extraterrestrial.:51–52 He later had several conversations on the subject in 1964 with Jacques Vallée. Though quite skeptical of any extraordinary answer to the UFO question, Sagan thought scientists should study the phenomenon, at least because there was widespread public interest in UFO reports.
Stuart Appelle notes that Sagan "wrote frequently on what he perceived as the logical and empirical fallacies regarding UFOs and the abduction experience. Sagan rejected an extraterrestrial explanation for the phenomenon but felt there were both empirical and pedagogical benefits for examining UFO reports and that the subject was, therefore, a legitimate topic of study."
In 1966 Sagan was a member of the Ad Hoc Committee to Review Project Blue Book, the U.S. Air Force's UFO investigation project. The committee concluded Blue Book had been lacking as a scientific study, and recommended a university-based project to give the UFO phenomenon closer scientific scrutiny. The result was the Condon Committee (1966–68), led by physicist Edward Condon, and in their final report they formally concluded that UFOs, regardless of what any of them actually were, did not behave in a manner consistent with a threat to national security.
Sociologist Ron Westrum writes that "The high point of Sagan's treatment of the UFO question was the AAAS' symposium in 1969. A wide range of educated opinions on the subject were offered by participants, including not only proponents such as James McDonald and J. Allen Hynek but also skeptics like astronomers William Hartmann and Donald Menzel. The roster of speakers was balanced, and it is to Sagan's credit that this event was presented in spite of pressure from Edward Condon." With physicist Thornton Page, Sagan edited the lectures and discussions given at the symposium; these were published in 1972 as UFO's: A Scientific Debate. Some of Sagan's many books examine UFOs (as did one episode of Cosmos) and he claimed a religious undercurrent to the phenomenon.
Sagan again revealed his views on interstellar travel in his 1980 Cosmos series. In one of his last written works, Sagan argued that the chances of extraterrestrial spacecraft visiting Earth are vanishingly small. However, Sagan did think it plausible that Cold War concerns contributed to governments misleading their citizens about UFOs, and that "some UFO reports and analyses, and perhaps voluminous files, have been made inaccessible to the public which pays the bills ... It's time for the files to be declassified and made generally available." He cautioned against jumping to conclusions about suppressed UFO data and stressed that there was no strong evidence that aliens were visiting the Earth either in the past or present.
After suffering from myelodysplasia, and receiving three bone marrow transplants, Sagan died of pneumonia at the age of 62 at the Fred Hutchinson Cancer Research Center in Seattle, Washington, on December 20, 1996. He was buried at Lakeview Cemetery in Ithaca, New York.
The 1997 movie Contact, based on Sagan's novel of the same name and finished after his death, ends with the dedication "For Carl". His photo can also be seen at 59:25 in the film.
In 1997 the Sagan Planet Walk was opened in Ithaca, New York. It is a walking-scale model of the Solar System, extending 1.2 km from the center of The Commons in downtown Ithaca to the Sciencenter, a hands-on museum. The exhibition was created in memory of Carl Sagan, who was an Ithaca resident and Cornell Professor. Professor Sagan had been a founding member of the museum's advisory board.
Sagan's son, Nick Sagan, wrote several episodes in the Star Trek franchise. In an episode of Star Trek: Enterprise entitled "Terra Prime", a quick shot is shown of the relic rover Sojourner, part of the Mars Pathfinder mission, placed by a historical marker at Carl Sagan Memorial Station on the Martian surface. The marker displays a quote from Sagan: "Whatever the reason you're on Mars, I'm glad you're there, and I wish I was with you." Sagan's student Steve Squyres led the team that landed the rovers Spirit and Opportunity successfully on Mars in 2004.
On November 9, 2001, on what would have been Sagan's 67th birthday, the Ames Research Center dedicated the site for the Carl Sagan Center for the Study of Life in the Cosmos. "Carl was an incredible visionary, and now his legacy can be preserved and advanced by a 21st century research and education laboratory committed to enhancing our understanding of life in the universe and furthering the cause of space exploration for all time", said NASA Administrator Daniel Goldin. Ann Druyan was at the Center as it opened its doors on October 22, 2006.
Sagan has at least three awards named in his honor:
- The Carl Sagan Memorial Award presented jointly since 1997 by the American Astronomical Society and The Planetary Society,
- The Carl Sagan Medal for Excellence in Public Communication in Planetary Science presented since 1998 by the American Astronomical Society's Division for Planetary Sciences (AAS/DPS) for outstanding communication by an active planetary scientist to the general public—Carl Sagan was one of the original organizing committee members of the DPS, and
- The Carl Sagan Award for Public Understanding of Science presented by the Council of Scientific Society Presidents (CSSP)—Sagan was the first recipient of the CSSP award in 1993.
Beginning in 2009, a musical project known as Symphony of Science sampled several excerpts of Sagan from his series Cosmos and remixed them to electronic music. To date, the videos have received over 21 million views worldwide on YouTube.
Awards and honors
- Annual Award for Television Excellence—1981—Ohio State University—PBS series Cosmos: A Personal Voyage
- Apollo Achievement Award—National Aeronautics and Space Administration
- NASA Distinguished Public Service Medal—National Aeronautics and Space Administration (1977)
- Emmy—Outstanding Individual Achievement—1981—PBS series Cosmos: A Personal Voyage
- Emmy—Outstanding Informational Series—1981—PBS series Cosmos: A Personal Voyage
- Exceptional Scientific Achievement Medal—National Aeronautics and Space Administration
- Helen Caldicott Leadership Award – Awarded by Women's Action for Nuclear Disarmament
- Hugo Award—1981—Best Dramatic Presentation—Cosmos: A Personal Voyage
- Hugo Award—1981—Best Related Non-Fiction Book—Cosmos
- Hugo Award—1998—Best Dramatic Presentation—Contact
- Humanist of the Year—1981—Awarded by the American Humanist Association 
- American Philosophical Society—1995—Elected to membership.
- In Praise of Reason Award—1987—Committee for the Scientific Investigation of Claims of the Paranormal
- Isaac Asimov Award—1994—Committee for the Scientific Investigation of Claims of the Paranormal
- John F. Kennedy Astronautics Award—1982—American Astronautical Society
- Special non-fiction Campbell Memorial Award—1974—The Cosmic Connection: An Extraterrestrial Perspective
- Joseph Priestley Award—"For distinguished contributions to the welfare of mankind"
- Klumpke-Roberts Award of the Astronomical Society of the Pacific—1974
- Konstantin Tsiolkovsky Medal—Awarded by the Soviet Cosmonauts Federation
- Locus Award 1986—Contact
- Lowell Thomas Award—The Explorers Club—75th Anniversary
- Masursky Award—American Astronomical Society
- Miller Research Fellowship—Miller Institute (1960–1962)
- Oersted Medal—1990—American Association of Physics Teachers
- Peabody Award—1980—PBS series Cosmos: A Personal Voyage
- Le Prix Galabert d’astronautique—International Astronautical Federation (IAF)
- Public Welfare Medal—1994—National Academy of Sciences
- Pulitzer Prize for General Non-Fiction—1978—The Dragons of Eden
- Science Fiction Chronicle Award—1998—Dramatic Presentation—Contact
- Named the "99th Greatest American" on June 5, 2005, Greatest American television series on the Discovery Channel
- Named an honorary member of the Demosthenian Literary Society on November 10, 2011
- New Jersey Hall of Fame—2009—Inductee.
- Sagan, Carl; Leonard, Jonathan Norton (1966). Planets. Life Science Library. Editors of Life. New York: Time, Inc. LCCN 66022436. OCLC 346361.
- ——; Shklovskii, I.S. (1966) [Originally published 1962 as Вселенная, жизнь, разум; Moscow: USSR Academy of Sciences Publisher]. Intelligent Life in the Universe. Authorized translation by Paula Fern. San Francisco: Holden-Day, Inc. LCCN 64018404. OCLC 317314.
- ——; Page, Thornton, eds. (1972). UFO's: A Scientific Debate. Ithaca, NY: Cornell University Press. ISBN 0-801-40740-0. LCCN 72004572. OCLC 415373.
- ——, ed. (1973). Communication with Extraterrestrial Intelligence (CETI). Cambridge, MA: MIT Press. ISBN 0-262-19106-7. LCCN 73013999. OCLC 700752.
- ——; Bradbury, Ray; Clarke, Arthur C. et al. (1973). Mars and the Mind of Man (1st ed.). New York: Harper & Row. ISBN 0-060-10443-0. LCCN 72009746. OCLC 613541.
- —— (1973). The Cosmic Connection: An Extraterrestrial Perspective. Produced by Jerome Agel (1st ed.). Garden City, NY: Anchor Press. ISBN 0-385-00457-5. LCCN 73081117. OCLC 756158.
- —— (1975). Other Worlds. Produced by Jerome Agel. Toronto, NY: Bantam Books. ISBN 0-552-66439-1. OCLC 3029556.
- —— (1977). The Dragons of Eden: Speculations on the Evolution of Human Intelligence (1st ed.). New York: Random House. ISBN 0-394-41045-9. LCCN 76053472. OCLC 2922889.
- ——; Drake, F. D.; Lomberg, Jon et al. (1978). Murmurs of Earth: The Voyager Interstellar Record (1st ed.). New York: Random House. ISBN 0-394-41047-5. LCCN 77005991. OCLC 4037611.
- —— (1979). Broca's Brain: Reflections on the Romance of Science (1st ed.). New York: Random House. ISBN 0-394-50169-1. LCCN 78021810. OCLC 4493944.
- —— (1980). Cosmos (1st ed.). New York: Random House. ISBN 0-394-50294-9. LCCN 80005286. OCLC 6280573.
- ——; Ehrlich, Paul R.; Kennedy, Donald et al. (1984). The Cold and the Dark: The World after Nuclear War: The Conference on the Long-Term Worldwide Biological Consequences of Nuclear War. Foreword by Lewis Thomas (1st ed.). New York: W. W. Norton & Company. ISBN 0-393-01870-9. LCCN 84006070. OCLC 10697281.
- ——; Druyan, Ann (1985). Comet (1st ed.). New York: Random House. ISBN 0-394-54908-2. LCCN 85008308. OCLC 811602694.
- —— (1985). Contact: A Novel. New York: Simon & Schuster. ISBN 0-671-43400-4. LCCN 85014645. OCLC 12344811.
- ——; Turco, Richard (1990). A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race (1st ed.). New York: Random House. ISBN 0-394-58307-8. LCCN 89043155. OCLC 20217496.
- ——; Druyan, Ann (1992). Shadows of Forgotten Ancestors: A Search for Who We Are (1st ed.). New York: Random House. ISBN 0-394-53481-6. LCCN 92050155. OCLC 25675747.
- —— (1994). Pale Blue Dot: A Vision of the Human Future in Space (1st ed.). New York: Random House. ISBN 0-679-43841-6. LCCN 94018121. OCLC 30736355.
- —— (1995). The Demon-Haunted World: Science as a Candle in the Dark (1st ed.). New York: Random House. ISBN 0-394-53512-X. LCCN 95034076. OCLC 779687822. (Note: errata slip inserted.)
- ——; Druyan, Ann (1997). Billions and Billions: Thoughts on Life and Death at the Brink of the Millennium (1st ed.). New York: Random House. ISBN 0-679-41160-7. LCCN 96052730. OCLC 36066119.
- —— (2006) [Edited from 1985 Gifford Lectures, University of Glasgow]. Druyan, Ann, ed. The Varieties of Scientific Experience: A Personal View of the Search for God. New York: Penguin Press. ISBN 1-59420-107-2. LCCN 2006044827. OCLC 69021064.
- Sagan 1994, p. 68
- Some of Carl Sagan's papers are available on the SAO/NASA Astrophysics Data System (ADS).
- "StarChild: Dr. Carl Sagan". StarChild. NASA. Retrieved October 8, 2009.
- Poundstone 1999, pp. 363–364, 374–375
- "Carl Sagan". Internet Accuracy Project. Grandville, MI: Internet Accuracy Project. Retrieved August 22, 2012.
- "Carl Sagan". The Famous People. The Famous People. Retrieved August 22, 2012.
- Davidson 1999
- Spangenburg & Moser 2004, pp. 2–5
- "Carl Sagan". Famous Scientists. famousscientists.org. Retrieved August 22, 2012.
- "American National Biography Online, Carl Sagan".
- "Ryerson Astronomical Society". Ryerson Astronomical Society (RAS). University of Chicago Department of Astronomy and Astrophysics. Retrieved August 22, 2012.
- Sagan, Carl (June 1960), Physical Studies of the Planets (dissertation), University of Chicago, p. ii,
A thesis in four parts submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Astronomy, University of Chicago, June, 1960.
- "Graduate students receive first Sagan teaching awards". University of Chicago Chronicle (University of Chicago News Office) 13 (6). November 11, 1993. Retrieved August 30, 2013.
- Head 2006, p. xxi
- Spangenburg & Moser 2004, p. 28
- Tatarewicz, Joseph N. (1990), Space Technology & Planetary Astronomy, Science, technology, and society, Bloomington, IN: Indiana University Press, p. 22, ISBN 0-253-35655-5
- "Happy (Belated) Birthday Carl!". University of California, Berkeley The Berkeley Science Review. Retrieved December 1, 2013.
- Morrison, David (January–February 2007). "Carl Sagan's Life and Legacy as Scientist, Teacher, and Skeptic". Skeptical Inquirer (Amherst, NY: Committee for Skeptical Inquiry) 31.1: 29–38. ISSN 0194-6730. Retrieved August 31, 2013.
- Sagan, Carl (January 5, 1995). An Interview with Carl Sagan. (Interview). Charlie Rose. PBS. New York. Retrieved August 30, 2013.
- Much of Sagan's research in the field of planetary science is outlined by William Poundstone. Poundstone's biography of Sagan includes an 8-page list of Sagan's scientific articles published from 1957 to 1998. Detailed information about Sagan's scientific work comes from the primary research articles. Example: Sagan, C.; Thompson, W.R.; Khare, B.N. (1992). "Titan: A Laboratory for Prebiological Organic Chemistry". Accounts of Chemical Research (Washington, D.C.: American Chemical Society) 25 (7): 286–292. doi:10.1021/ar00019a003. There is commentary on this research article about Titan at David J. Darling's The Encyclopedia of Science.
- Pafumi, G.R. (2010). Is Our Vision of God Obsolete?: Often What We Believe is not What We Observe. Bloomington, IN: Xlibris. p. 338. ISBN 978-1-4415-9041-1. OCLC 710798384. Retrieved August 30, 2013.
- Sagan, Carl (1985) [Originally published 1980]. Cosmos (1st Ballantine Books ed.). New York: Ballantine Books. ISBN 0-345-33135-4. LCCN 80005286. OCLC 12814276.
- "Sagan, Carl Edward". Columbia Encyclopedia (Sixth ed.). New York: Columbia University Press. May 2001. Archived from the original on October 11, 2007. Retrieved August 30, 2013.
- "Carl Sagan". Pasadena, CA: The Planetary Society. Retrieved August 30, 2013.
- Benford, Gregory (1997). "A Tribute to Carl Sagan: Popular & Pilloried". Skeptic (The Skeptics Society) 13 (1).
- Shermer, Michael. "Candle in the Dark". The Works of Michael Shermer. Michael Shermer. Retrieved March 10, 2013. Article originally published in November 2003 issue of Scientific American.
- Impey, Chris (January–February 2000). "Carl Sagan, Carl Sagan: Biographies Echo an Extraordinary Life". American Scientist (Book review) (Sigma Xi) 88 (1). ISSN 0003-0996. Retrieved March 10, 2013.
- "Christmas Lectures 1977: The Planets : Ri Channel". Ri Channel. London: Royal Institution of Great Britain. Retrieved February 7, 2012.
- Vergano, Dan (March 16, 2014). "Who Was Carl Sagan?". National Geographic Daily News. Washington, D.C.: National Geographic Society. Retrieved May 13, 2014.
- "Cosmos". Academy of Television Arts & Sciences. Retrieved September 4, 2013.
- "Carl Sagan". EMuseum. Minnesota State University, Mankato. Archived from the original on May 28, 2010. Retrieved August 30, 2013.
- "CosmoLearning Astronomy". CosmoLearning. Retrieved October 8, 2009.
- Golden, Frederic (October 20, 1980). "The Cosmic Explainer". Time. Retrieved August 30, 2013.
- Turco, R.P.; Toon, O.B.; Ackerman, T.P.; Pollack, J.B.; Sagan, C. (January 12, 1990). "Climate and smoke: an appraisal of nuclear winter". Science (Washington, D.C.: American Association for the Advancement of Science) 247 (4939): 166–176. doi:10.2307/2873486. Retrieved August 31, 2013. JSTOR link to full text article. Carl Sagan discussed his involvement in the political nuclear winter debates and his erroneous global cooling prediction for the Gulf War fires in his book, The Demon-Haunted World.
- US Military History Companion
- "Meet Carl Sagan". The Science Channel. Discovery Communications. Archived from the original on May 18, 2007. Retrieved August 31, 2013.
- "PAGE 1 OF 2: Burning oil wells could be disaster, Sagan says January 23, 1991".
- Wilmington morning Star January 21’st, 1991
- Hirschmann, Kris. "The Kuwaiti Oil Fires". Facts on File.
- "FIRST ISRAELI SCUD FATALITIES OIL FIRES IN KUWAIT". Nightline. yes. 1991-01-22. ABC.
- "IV. AIR POLLUTANTS FROM OIL FIRES AND OTHER SOURCES".
- Sagan 1995, p. 257
- Jost, Hans-Jürg; Drdla, Katja; Stohl, Andreas et al. (June 2, 2004). "In-situ observations of mid-latitude forest fire plumes deep in the stratosphere" (PDF). Geophysical Research Letters (Washington, D.C.: American Geophysical Union) 31 (11). Bibcode:2004GeoRL..3111101J. doi:10.1029/2003GL019253. CiteID L11101. Retrieved August 31, 2013.
- Averill, Clare; Logan, Jennifer (August 19, 2004). "Smoke Soars to Stratospheric Heights". Earth Observatory. NASA. Retrieved March 10, 2013.
- Fromm, Michael; Alfred, Jerome; Hoppel, Karl et al. (May 1, 2000). "Observations of boreal forest fire smoke in the stratosphere by POAM III, SAGE II, and lidar in 1998". Geophysical Research Letters (Washington, D.C.: American Geophysical Union) 27 (9): 1407–1410. Bibcode:2000GeoRL..27.1407F. doi:10.1029/1999GL011200. Archived from the original on January 6, 2009. Retrieved August 29, 2013.
- Fromm, M.; Stocks, B.; Servranckx, R. et al. (2006). "Smoke in the Stratosphere: What Wildfires have Taught Us About Nuclear Winter". Eos, Transactions, American Geophysical Union (Washington, D.C.: American Geophysical Union) 87 (52 Fall Meet. Suppl.): Abstract U14A–04. Bibcode:2006AGUFM.U14A..04F.
- Head 2006, p. 86–87
- Morrison, David (October 3, 2007). "Taking a Hit: Asteroid Impacts & Evolution". Astronomical Society of the Pacific (Podcast). Astronomical Society of the Pacific. Retrieved August 31, 2013.
- Sagan, Carl; Ostro, Steven J. (Summer 1994). "Long-Range Consequences Of Interplanetary Collisions" (PDF). Issues in Science and Technology (Washington, D.C.: National Academy of Sciences) 10 (4): 67–72. Bibcode:1994IST....10...67S. ISSN 0748-5492. Retrieved August 31, 2013.
- Gault, Matthew (28 November 2013). "When Earth Dreamed of Nuking the Moon". medium.com. War is Boring. Retrieved 28 November 2013.
- Sagan, Carl (writer/host) (November 9, 1980). "The Backbone of Night". Cosmos: A Personal Voyage. Episode 7. PBS.
- Dicke, William (December 21, 1996). "Carl Sagan, an Astronomer Who Excelled at Popularizing Science, Is Dead at 62". The New York Times. Retrieved August 31, 2013.
- Sagan & Druyan 1997, pp. 3–4
- Shapiro, Fred R., ed. (2006). The Yale Book of Quotations. Foreword by Joseph Epstein. New Haven, CT: Yale University Press. p. 660. ISBN 978-0-300-10798-2. LCCN 2006012317. OCLC 66527213.
- Frazier, Kendrick, ed. (July–August 2005). "Carl Sagan Takes Questions: More From His 'Wonder and Skepticism' CSICOP 1994 Keynote". Skeptical Inquirer (Amherst, NY: The Committee for Skeptical Inquiry) 29.4. Retrieved March 25, 2010.
- "Sagan". Dictionary.com Unabridged. Random House. Retrieved August 31, 2013. Jargon File 4.2.0.
- Safire, William (April 17, 1994). "Footprints on the Infobahn". The New York Times. Retrieved August 31, 2013.
- Gresshoff, P.M. (2004). "Scheel D. and Wasternack C.(eds) Plant Signal Transduction" (PDF). Annals of Botany (Book review) (Oxford University Press) 93 (6): 783–784. doi:10.1093/aob/mch102. Retrieved August 31, 2013.
- Druyan, Ann (November 2000). "A New Sense of the Sacred Carl Sagan's 'Cosmic Connection'". The Humanist (Washington, D.C.: American Humanist Association) 60 (6). Retrieved August 29, 2013.
- Spangenburg & Moser 2004, p. 106
- Rethinking Risk and the Precautionary Principle, edited by Julian Morris. pg 116
- Women On War, Daniela Gioseffi.
- Atheists in America edited by Melanie E. Brewster pg 102
- Asimov, Isaac (1981) [Originally published 1980; Garden City, NY: Doubleday]. In Joy Still Felt: The Autobiography of Isaac Asimov, 1954–1978. New York: Avon. pp. 217, 302. ISBN 0-380-53025-2. LCCN 79003685. OCLC 7880716.
- Sagan, Carl (1980) [Originally published 1979]. Broca's Brain: Reflections on the Romance of Science (Reprint ed.). New York: Ballantine Books. p. 330. ISBN 0-345-33689-5. LCCN 78021810. OCLC 428008204.
- "Quotes on Religion – Carl Sagan". Atheism.about.com. IAC. Retrieved March 10, 2013.
- Head 2006, p. 70
- Schei, Kenneth A. (1996). An Atheist for Jesus. Synthesis. ISBN 0-926491-01-6.
- Bennett, Jeffrey O.; Donahue, Megan O.; Schneider, Nicholas et al. (2009). The Cosmic Perspective (6th (student) ed.). Boston: Addison-Wesley. ISBN 978-0-321-63366-8. LCCN 2009040910. OCLC 569911190.
- "Preserving and Cherishing the Earth". The Yale Forum on Religion and Ecology. 2013. Retrieved 9 November 2013.
- Head, Tom (1997). "Conversations with Carl". Skeptic (The Skeptics Society) 13 (1): 32–38. Excerpted in Head 2006
- Sagan, Carl (1997) [Originally published 1995]. The Demon-Haunted World: Science as a Candle in the Dark (1st Ballantine Books ed.). New York: Ballantine Books. p. 278. ISBN 0-345-40946-9. LCCN 95034076. OCLC 36504316.
- Tracy, David (1990). "Kenosis, Sunyata, and Trinity: A Dialogue with Masao Abe". In Cobb, John B., Jr.; Ives, Christopher. The Emptying God: A Buddhist-Jewish-Christian Conversation. Faith Meets Faith Series. Essays by Masao Abe. Maryknoll, NY: Orbis Books. p. 52. ISBN 0-883-44670-7. LCCN 90031442. OCLC 318355646.[page verification needed]
- edited by Lynn Margulis, Dorion Sagan (2007). Dazzle Gradually: Reflections on the Nature of Nature. Chelsea Green Publishing. p. 14. ISBN 1933392312.
- Druyan, Ann (November–December 2003). "Ann Druyan Talks About Science, Religion, Wonder, Awe ... and Carl Sagan". Skeptical Inquirer (Amherst, NY: Committee for Skeptical Inquiry) 27.6. ISSN 0194-6730. Retrieved July 27, 2010.
- Sagan, Carl (writer/host) (December 14, 1980). "Encyclopaedia Galactica". Cosmos: A Personal Voyage. Episode 12. 01:24 minutes in. PBS.
- Rawson, Hugh (2008). "Sagan's Standard". The Unwritten Laws of Life. CSBC Ltd. Archived from the original on January 12, 2012. Retrieved September 1, 2013.
- Truzzi, Marcello (1978). "On the Extraordinary: An Attempt at Clarification" (PDF). Zetetic Scholar 1 (1): 11.
- Truzzi, Marcello (1998). Binkowski, Edward, ed. "On Some Unfair Practices towards Claims of the Paranormal". Oxymoron: Annual Thematic Anthology of the Arts and Sciences (New York: Oxymoron Media, Inc.). 2: The Fringe. ISSN 1090-2236. OCLC 35240974. Retrieved September 1, 2013.
- Flournoy, Théodore (1983) [Originally published 1899; Geneva: Édition Atar]. Des Indes à la Planète Mars: Étude sur un cas de Somnambulisme avec Glossolalie [From India to the Planet Mars: A Study of a Case of Somnambulism with Glossolalia] (in French). Introduction by Hélène Boursinhac; translation by Daniel B. Vermilye (Reprint ed.). Geneva: Éditions Slatkine. pp. 344–345. ISBN 2-05-100499-4. OCLC 11558608.
- Sagan 1980 (1985 ed.), p. 108
- Grinspoon, Lester (1994) [2nd ed. published 1977; Cambridge, MA: Harvard University Press]. Marihuana Reconsidered. New introduction by author (2nd (reprint) ed.). Oakland, CA: Quick American Archives. ISBN 0-932551-13-0. LCCN 77076767. OCLC 32410025.
- Sagan, Carl. "Mr. X". Marijuana-Uses.com. Retrieved August 7, 2009.
- Whitehouse, David (October 15, 1999). "Carl Sagan: A life in the cosmos". BBC News (BBC). Retrieved August 30, 2013.
- Davidson, Keay (August 22, 1999). "Billions and Billions of '60s Flashbacks". The San Francisco Examiner. Retrieved May 2, 2007.
- Larsen, Dana (November 1, 1999). "Carl Sagan: toking astronomer". Cannabis Culture (Vancouver, B.C.). Retrieved May 2, 2007.
- "Foundation Board of Directors". NORML.org. Washington, D.C.: NORML and the NORML Foundation. August 13, 2010. Archived from the original on January 4, 2011. Retrieved September 2, 2013.
- "Ann Druyan". NORML.org. Washington, D.C.: NORML and the NORML Foundation. Retrieved July 20, 2011.
- Poundstone 1999, p. 364
- Linzmayer, Owen; Chaffin, Bryan (November 15, 2004). "This Week in Apple History: November 14–20: McIntosh, IIe Killed, Butt-Head Astronomer". The Mac Observer (The Mac Observer, Inc.). Retrieved July 23, 2012.
- Sagan v. Apple Computer, Inc., 874 F.Supp. 1072 (USDC C.D. Cal. 1994), CV 94-2180 LGB (BRx); 1994 U.S. Dist. LEXIS 20154.
- Poundstone 1999, p. 374
- Poundstone 1999, pp. 374–375
- Sagan, Carl (2000) [Originally published 1973]. "'Hello, Central Casting? Send Me Twenty Extraterrestrials'". Carl Sagan's Cosmic Connection: An Extraterrestrial Perspective. Produced by Jerome Agel; new contributions by Freeman Dyson, Ann Druyan, and David Morrison (2nd ed.). Cambridge; New York: Cambridge University Press. p. 183. ISBN 0-521-78303-8. LCCN 00020378. OCLC 460747781.
- Westrum, Ron (2000). "Limited Access: Six Natural Scientists and the UFO Phenomenon". In Jacobs, David M.. UFOs and Abductions: Challenging the Borders of Knowledge. Lawrence, KS: University Press of Kansas. pp. 31–55. ISBN 0-7006-1032-4. LCCN 00028970. OCLC 43615835.
- Appelle, Stuart (2000). "Ufology and Academia: The UFO Phenomenon as a Scholarly Discipline". In Jacobs, David M. UFOs and Abductions: Challenging the Borders of Knowledge. Lawrence, KS: University Press of Kansas. pp. 7–30. ISBN 0-7006-1032-4. LCCN 00028970. OCLC 43615835.
- Sagan 1995, pp. 81–96, 99–104
- Quarles, Norma (December 20, 1996). "Carl Sagan dies at 62". CNN. Retrieved December 5, 2011.
Sagan was a noted astronomer whose lifelong passion was searching for intelligent life in the cosmos.
- Carl Sagan at Find a Grave
- "Sagan Planet Walk". sciencenter.org. Ithaca, NY: Sciencenter. Retrieved March 10, 2013.
- "Sagan Award for Public Understanding of Science". Council of Scientific Society Presidents. Archived from the original on July 26, 2007. Retrieved May 2, 2007.
- "The 2007 IIG Awards". IIG. Los Angeles: Independent Investigations Group. August 18, 2007. Retrieved July 1, 2011.
- Boswell, John (November 9, 2009). A Glorious Dawn (7-in (17.5 cm) gramophone record). Nashville, TN: Third Man Records. Retrieved September 3, 2013.
- "From the AHA archives: Carl Sagan's 1981 Humanist of the year speech". americanhumanist.org. Retrieved 25 December 2014.
- "American Philosophical Society Member History". Philadelphia, PA: American Philosophical Society. Retrieved September 3, 2013.
- "John F. Kennedy Astronautics Award". Springfield, VA: American Astronautical Society. Retrieved September 3, 2013.
- "The John W. Campbell Memorial Award". Lawrence, KS: Center for the Study of Science Fiction. Retrieved September 3, 2013.
- "Public Welfare Medal". Washington, D.C.: National Academy of Sciences. Retrieved February 18, 2011.
- Mascarenhas, Rohan (May 3, 2009). "2009 New Jersey Hall of Fame inductees welcomed at NJPAC". The Star-Ledger (Newark, NJ: Advance Publications). Retrieved September 3, 2013.
- Terzian, Yervant; Bilson, Elizabeth, eds. (1997). Carl Sagan's Universe. Cambridge; New York: Cambridge University Press. ISBN 0-521-57603-2. LCCN 96040511. OCLC 36130681.
- Achenbach, Joel (1999). Captured by Aliens: The Search for Life and Truth in a Very Large Universe. New York: Simon & Schuster. ISBN 0-684-84856-2. LCCN 99037592. OCLC 41606346.
- Davidson, Keay (1999). Carl Sagan: A Life. New York: John Wiley & Sons. ISBN 0-471-25286-7. LCCN 99036206. OCLC 41580617.
- Poundstone, William (1999). Carl Sagan: A Life in the Cosmos. New York: Henry Holt and Company. ISBN 0-8050-5766-8. LCCN 99014615. OCLC 40979822.
- Spangenburg, Ray; Moser, Kit (2004). Carl Sagan: A Biography. Westport, CT: Greenwood Publishing Group. ISBN 0-313-32265-1. LCCN 2004015176. OCLC 55846272.
- Head, Tom, ed. (2006). Conversations with Carl Sagan (1st ed.). Jackson, MS: University Press of Mississippi. ISBN 1-57806-736-7. LCCN 2005048747. OCLC 60375648.
- Morrison, David (2006). "Carl Sagan: The People's Astronomer". AmeriQuests (Nashville, TN: Vanderbilt University) 3 (2). ISSN 1553-4316. Retrieved August 30, 2013.
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|Definitions from Wiktionary|
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|Source texts from Wikisource|
- The Carl Sagan Portal
- Sagan interviewed by Ted Turner, CNN, 1989, video: 44 minutes.
- Video of skit on YouTube from The Tonight Show Starring Johnny Carson mentioning "billions and billions"
- BBC Radio program "Great Lives" on Carl Sagan's life
- "A man whose time has come"—Interview with Carl Sagan by Ian Ridpath, New Scientist, July 4, 1974
- Carl Sagan at the Internet Movie Database
- Works by or about Carl Sagan in libraries (WorldCat catalog)
- Carl Sagan Prize for Science Popularization at Wonderfest
- Carl Sagan Center for the Study of Life in the Universe, SETI Institute
- "Carl Sagan's Life and Legacy as Scientist, Teacher, and Skeptic", by David Morrison, Committee for Skeptical Inquiry
- "A Tribute to Carl Sagan: Our Place in the Universe", by Bill Nye, The Skeptics Society
- Sagan Medal for Excellence in Public Communication in Planetary Science, presented by the American Astronomical Society's Division for Planetary Sciences (AAS/DPS)