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Carl Edward Sagan (November 9, 1934 – December 20, 1996) was an Americanmarker astronomer, astrochemist, author, and highly successful popularizer of astronomy, astrophysics and other natural sciences. He pioneered exobiology and promoted the Search for Extra-Terrestrial Intelligence .

He is world-famous for writing popular science books and for co-writing and presenting the award-winning 1980 television series Cosmos: A Personal Voyage, which has been seen by more than 500 million people in over 60 countries. A book to accompany the program was also published. He also wrote the novel Contact, the basis for the 1997 film of the same name. One of the last books he wrote was Pale Blue Dot. During his lifetime, Sagan 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 frequently advocated skeptical inquiry, secular humanism, and the scientific method.

Early life and education

Carl Sagan was born in Brooklynmarker, New Yorkmarker, to a Russian Jewish family. His father, Sam Sagan, was a Russian immigrant garment worker; his mother, Rachel Molly Gruber, a housewife. Carl was named in honor of Rachel's biological mother, Chaiya Clara, "the mother she never knew", in Sagan's words.Sagan graduated from Rahway High Schoolmarker in Rahway, New Jerseymarker in 1951. He attended the University of Chicagomarker, where he participated in the Ryerson Astronomical Society, received a B.A. with general and special honors (1954), a B.S. (1955) and a M.S. (1956) in physics, before earning a Ph.D. degree (1960) in astronomy and astrophysics. During his time as an undergraduate, Sagan spent some time working in the laboratory of the geneticist H. J. Muller. From 1960 to 1962 he was a Miller Fellow at the University of California, Berkeleymarker.

Career in science

From 1962 to 1968, Sagan worked at the Smithsonian Astrophysical Observatorymarker in Cambridge, Massachusetts. Sagan lectured and did research annually at Harvard Universitymarker until 1968, when he moved to Cornell Universitymarker in New Yorkmarker. He became a full Professor at Cornell in 1971, and he directed the Laboratory for Planetary Studies there. From 1972 to 1981, Sagan was the Associate Director of the Center for Radio Physics and Space Research at Cornell.

Sagan was a scientist connected with the American space program since its inception. From the 1950s onward, he worked as an adviser to NASAmarker. One of his many duties during his tenure at the space agency 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 during his lifetime, 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 throughout his lifetime; 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 Space Station at the expense of further robotic missions.

At Cornell University, Sagan taught a course on critical thinking until his death in 1996 from a rare bone marrow disease. The course had only a limited number of seats. Although hundreds of students applied each year, only about 20 were chosen to attend each semester. The course was discontinued immediately after Sagan's death, but it was resumed by Dr. Yervant Terzian in 2000.

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 Laboratorymarker, 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 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 for life. Europa's subsurface ocean of water was later indirectly confirmed by the spacecraft Galileo. Sagan also helped solve the mystery of the reddish haze seen on Titan, revealing that it is composed of complex organic molecules constantly raining down onto the moon's surface.

He further contributed insights regarding the atmospheres of Venus and Jupiter as well as seasonal changes on Mars. Sagan established that the atmosphere of Venus is extremely hot and dense with pressures increasing steadily all the way down to the surface. 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 but shifts in surface dust caused by windstorms.

He is also the 1994 recipient of the Public Welfare Medal, the highest award of the National Academy of Sciencesmarker for "distinguished contributions in the application of science to the public welfare."

Science advocacy

Sagan's ability to convey his ideas allowed many people to better understand the cosmos—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 at the Royal Institutionmarker in Londonmarker. He hosted and, with Ann Druyan, co-wrote and co-produced the highly popular thirteen-part PBS television series Cosmos: A Personal Voyage modeled on Jacob Bronowski's The Ascent of Man.

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 the Public Broadcasting Service 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.

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, but did not live to see the book's 1997 motion picture adaptation, which starred Jodie Foster and won the 1998 Hugo Award.

From Cosmos and his frequent appearances on The Tonight Show, Sagan became associated with the catch phrase "billions and billions". As Sagan himself stated, 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":

However, his 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" in viewers' minds), made him a favorite target of comic performers including Johnny Carson, Gary Kroeger, Mike Myers,Myers portrayed Sagan in "SNL: Carl Sagan's Global Warming Christmas Special [VIDEO]"/> Bronson Pinchot, 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 catch phrase, observing that Carson himself was an amateur astronomer and that Carson's comic caricature often included real science.

As a humorous tribute to him, a Sagan has been defined as a humorous unit of measurement equal to at least four billion, since the lower bound of a number conforming to the constraint of billions and billions must be two billion plus two billion. Assuming one uses the short scale definition for billion, there are nearly 100 Sagan (400,000,000,000) stars in the Milky Way galaxy.

Whilst Sagan was outspoken about political issues, the popular perception of his characterization of large cosmic quantities continued to be a sense of 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", however this famous saying was widely misunderstood, as he was in fact referring, in his Cosmos series, to the world being at a "critical branch point in history where our actions will propagate down through the centuries" as in the following quote from Cosmos: A personal Voyage: Episode 8: Journeys in Space and Time:

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 an introduction for the bestselling book by Stephen Hawking, 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 passing, David Morrison, a former student of Sagan, recalled "Sagan's immense contributions to planetary research, the public understanding of science, and the skeptical movement" in Skeptical Inquirer.

Sagan erroneously predicted in January 1991 that so much smoke from the Kuwaiti oil fires "might get so high as to disrupt agriculture in much of South Asia…" He acknowledged the error in The Demon-Haunted World: "as events transpired, 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."

In his later years Sagan advocated the creation of an organized search for near Earth objects 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 also create the ability to deflect an asteroid towards the Earth—providing an evil power with a true doomsday bomb.

In 1994, Apple Computermarker began developing the Power Macintosh 7100. They chose the internal code name "Carl Sagan", the reference being that the mid-range PowerMac 7100 should make Apple "billions and billions." Though the internal project name was never used in public marketing, it did come up in Usenet postings and news of the name grew from there. When Sagan learned of this he sued Apple Computer to force the use of a different project name. Other models released conjointly had code names such as "Cold fusion" and "Piltdown Man", and Sagan was displeased at being associated with what he considered pseudoscience. (He was at the time writing a book discrediting pseudoscience.) Though Sagan lost the lawsuit Apple engineers complied with his demands anyway and renamed the project "BHA" (for Butt-Head Astronomer). Sagan promptly sued Apple for libel over the new name, claiming that it subjected him to contempt and ridicule, but he lost this lawsuit as well. Still, the 7100 saw another name change: it was finally referred to internally as "LAW" (Lawyers Are Wimps).


Sagan was well known for his research on the possibilities of extraterrestrial life, including experimental demonstration of the production of amino acids from basic chemicals by radiation. Sagan was a proponent of the search for extraterrestrial life. He urged the scientific community to listen with radio telescopes for signals from intelligent extraterrestrial life-forms. So persuasive was he 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 turnaround in the respectability of this controversial field. Sagan also helped Dr. Frank Drake write the Arecibo message, a radio message beamed into space from the Arecibo radio telescopemarker on November 16, 1974, aimed at informing 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.

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 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.

In 1966, Sagan was asked to contribute an interview about the possibility of extraterrestrials to a proposed introduction to the film 2001: A Space Odyssey. Sagan reportedly asked for control and a percentage of the film's box office receipts in return; these terms were rejected.

UFO skepticism

Sagan was skeptical of reports of UFOs. He thought scientists and investigators should examine them to address the widespread public interest in UFO reports. In 1964, he had several conversations on the subject with Jacques Vallee.

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 (1966–1968), 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.

Ron Westrum writes that "The high point of Sagan's treatment of the UFO question was the AAAS's 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 UFOs: 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.

Religious stance and social concerns

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.

Sagan, however, denied that he was an atheist: "An atheist has to know a lot more than I know." In reply to a question in 1996 about his religious beliefs, Sagan answered, "I'm agnostic." 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.

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." This was based on a nearly identical statement by fellow founder of the Committee for the Scientific Investigation of Claims of the Paranormal founder Marcello Truzzi, "Extraordinary claims require extraordinary proof." This idea originated with Pierre-Simon Laplace (1749-1827), a Frenchmarker mathematician and astronomer who said, "The weight of evidence for an extraordinary claim must be proportioned to its strangeness." Sagan nominated three areas within paranormal research that he considered to have sufficient experimental support, albeit dubious, to warrant serious study. These related to thoughts barely affecting random number generators (psychokinesis); projection of images from one person to another (telepathy); and young children sometimes reporting verifiable details of previous lives (reincarnation research). He was at pains to point out that he was not convinced by the validity of these contentions, merely that they might be true.

Late in his life, Sagan's books elaborated on his skeptical, naturalistic view of the world. In The Demon-Haunted World: Science as a Candle in the Dark, 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 for 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 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 to this aspect of Sagan's life.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.

Nuclear weapons

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?" 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.

At the height of the Cold War, Sagan became involved in public awareness efforts for the effects of nuclear war when a mathematical climate model suggested that a substantial nuclear exchange could upset the delicate balance of life on Earth. He was one of five authors—the "S" of the "TTAPS" report as the research paper came to be known. He eventually co-authored the scientific paper hypothesizing a global nuclear winter following nuclear war. He also co-authored the book A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race, a comprehensive examination of the phenomenon of nuclear winter.

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 Unionmarker, 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 Sitemarker, 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.

Death and legacy

Stone dedicated to Carl Sagan in the Celebrity Path of the Brooklyn Botanic Garden

After a long and difficult fight with myelodysplasia, which included three bone marrow transplants, Sagan died of pneumonia at the age of 62 at the Fred Hutchinson Cancer Research Center in Seattle, Washingtonmarker on December 20, 1996. After landing, the unmanned Mars Pathfinder spacecraft was renamed the Carl Sagan Memorial Station on July 5, 1997. Asteroid 2709 Sagan is also named in his honor. He was buried at Lakeview Cemetery in Ithaca, New Yorkmarker.

The 1997 movie Contact, based on Sagan's novel of the same name and finished after his death, ends with the dedication "For Carl".

On November 9, 2001, on what would have been Sagan's 67th birthday, the NASA Ames Research Centermarker 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'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 Spirit Rover and Opportunity Rover successfully on Mars in 2004.

Sagan has at least three awards named in his honor: In 2006, the Carl Sagan Medal was awarded to astrobiologist and author David Grinspoon, the son of Sagan's friend Lester Grinspoon.

On December 20, 2006, the tenth anniversary of Sagan's death, a blogger, Joel Schlosberg, organized a Carl Sagan "blog-a-thon" to commemorate Sagan's death, and the idea was supported by Nick Sagan. Many members of the blogging community participated.

In 2008, Benn Jordan, also known as The Flashbulb, released the album "Pale Blue Dot: A Tribute to Carl Sagan".

In 2009, clips from Carl Sagan's Cosmos were used as the basis for A Glorious Dawn, the first video produced for the Symphony of Science, an educational music video production by composer John Boswell. Musician Jack White later released this song as a vinyl single under his record label Third Man Records. Additional clips were used in the followup video, We Are All Connected, which featured Sagan alongside other noted scientists Richard Feynman, Neil Degrasse Tyson, and Bill Nye.

Also in 2009, the 75th anniversary of Carl Sagan's birth, the First "Carl Sagan Day" has been celebrated on November 7.

Awards and honors

NASA Distinguished Public Service Medal

Personal life

Sagan married three times: in 1957, to biologist Lynn Margulis, mother of Dorion Sagan and Jeremy Sagan; in 1968, to artist Linda Salzman, mother of Nick Sagan; and in 1981, to author Ann Druyan, mother of Alexandra Rachel (Sasha) Sagan and Samuel Democritus Sagan. His marriage to Druyan continued until his death in 1996.



Further reading

  • Morrison, David (2006). Carl Sagan: The People's Astronomer. AmeriQuests, vol. 3. no. 2: PDF.
  • 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. Includes detailed account of Sagan's role in the search for extraterrestrial life.

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