Carl Sagan

• 1. Introduction

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  Carl Sagan grew up in a modest Bensonhurst apartment with parents who, by his own account, "knew almost nothing about science." Yet it was precisely those parents who set him on a path that would eventually lead hundreds of millions of people to look at the night sky differently. How does a garment worker's son from Brooklyn become the most cited scientist in the history of the Search for Extraterrestrial Intelligence? How does a boy who once asked a librarian for a book on stars and received a picture book of movie stars instead wind up assembling the first physical message ever launched from Earth into deep space?

  Those questions carry us through a life that stretched from the Bensonhurst streets to the corridors of NASA, from Harvard lecture halls to Nevada nuclear test sites where Sagan was twice arrested climbing chain-link fences in protest. He published more than 600 scientific papers. He co-wrote and narrated a documentary series seen by at least 500 million people across 60 countries. He won a Pulitzer Prize and helped coin the term "nuclear winter." He built golden records to speak for all humanity and sent them riding on spacecraft past the edge of the solar system.

  The man who made the universe feel personal died of pneumonia on the 20th of December, 1996, at the age of 62. But the story of how he got there begins with a time capsule buried at Flushing Meadows and a library book that finally had the right kind of stars inside it.

• 2. Brooklyn to the Cosmos

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  At the 1939 New York World's Fair, a young Carl Sagan watched workers lower a time capsule into the ground at Flushing Meadows, a container of mementos from the 1930s intended for a far future. His biographer Keay Davidson wrote that this "thrilled Carl." It was, in retrospect, a rehearsal: as an adult, Sagan would help send time capsules not into the soil but into interstellar space.

  Sagan was born on the 9th of November, 1934, to Samuel Sagan, a Ukrainian-born garment worker who had emigrated from Kamianets-Podilskyi, and Rachel Molly Gruber, a housewife who had grown up poor in New York City during World War I. Davidson suggested that Rachel "worshipped her only son" because she hoped he would fulfill the intellectual ambitions her poverty, gender, and ethnicity had blocked. Sagan traced his analytical drive directly to her. His wonder, he said, came from his father, a man who spent free time giving apples to the poor and mediating labor disputes in the garment district.

  Sagan himself pinpointed the exact moment the cosmos seized him. At a neighborhood library, he asked for a book on stars and was briefly handed a volume about film actors. The correct book arrived and delivered a revelation: the stars were suns, only unimaginably distant. "The scale of the universe suddenly opened up to me," he recalled. "It was a kind of religious experience. There was a magnificence to it, a grandeur, a scale which has never left me."

  By age six or seven, he and a close friend were making regular trips to the Hayden Planetarium. His parents bought him chemistry sets and reading matter. In 1947, he discovered the magazine Astounding Science Fiction, which he read so voraciously that he devised scoring systems for the stories the way other boys kept baseball statistics. The science fiction author Edgar Rice Burroughs deepened his fixation on other worlds through the John Carter of Mars novels. The hunger to understand the cosmos, per biographer Ray Spangenburg, became a "driving force in his life, a continual spark to his intellect."

• 3. Education and Early Controversies

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  At Rahway High School in New Jersey, teachers recognized Sagan's abilities immediately. An administrator told his parents, "This kid ought to go to a school for gifted children, he has something really remarkable." His family could not afford private school, so he stayed and built his own chemistry laboratory at home, taught himself molecular structure using cardboard cutouts, and became president of the school's chemistry club.

  Before graduating in 1951, Sagan entered an essay contest exploring a then-controversial idea: that humanity's first contact with advanced extraterrestrials might prove as catastrophic for people on Earth as the arrival of Europeans had been for Native Americans. His rhetorical skill won over the judges and earned him first prize. His classmates, less concerned with the stars, voted him most likely to succeed.

  He enrolled at the University of Chicago at sixteen, one of the few schools willing to accept a student that young. Chancellor Robert M. Hutchins had rebuilt the college around Great Books, Socratic dialogue, and comprehensive examinations. Sagan wrote that he found there "teachers who not only understood science, but were actually able to explain it." He sat in a physics department that orbited around Enrico Fermi, learned mathematical elegance from Subrahmanyan Chandrasekhar, discussed chemistry with Harold Urey, and studied planetary astronomy under Gerard Kuiper, who was at that time its only full-time practitioner.

  The Miller-Urey experiment of 1952 ignited his interest in the origin of life, and he wrote his doctoral thesis, "Physical Studies of the Planets," under Kuiper's direction, earning his doctorate in astronomy and astrophysics in 1960. Kuiper taught him the back-of-the-envelope calculation: a quick estimate on a scrap of paper that could cut through nonsense, as Sagan put it, "like a knife through butter."

  In 1958, he and Kuiper worked on a classified Air Force project to detonate a nuclear warhead on the Moon. Sagan held both a Top Secret Air Force clearance and a Secret NASA clearance. In 1999, a journal article revealed he had inadvertently listed classified project titles in a 1959 scholarship application to the University of California, Berkeley, a security lapse confirmed in a follow-up letter by project leader Leonard Reiffel.

• 4. The Harvard Rejection and Cornell

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  Harvard University astronomer Fred Whipple initially invited Sagan to give a colloquium after reading his 1961 article in the journal Science on the atmosphere of Venus. That invitation eventually expanded into an assistant professorship. Sagan worked there from 1963 until 1968, splitting his time between Harvard and the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.

  In 1968, Harvard denied him tenure. The decision, Sagan later said, was very unexpected. Critics within the institution argued that his interests ranged too widely across disciplines when academic custom rewarded narrow specialization. His former undergraduate adviser Harold Urey, who had once praised Sagan's curiosity, wrote a letter to the tenure committee recommending strongly against him. Because Urey held a Nobel Prize, his opinion carried particular weight. Fred Whipple had wanted Harvard to keep Sagan, but Urey's letter proved decisive.

  Cornell astronomer Thomas Gold had been trying to recruit Sagan to Ithaca for years, dangling the prospect of working alongside the recently hired Frank Drake. After the Harvard rejection, Sagan accepted. He joined Cornell's faculty and never left, remaining there for nearly 30 years until his death.

  Cornell's astronomy department took a different view of his celebrity. He became a full professor in 1970 and directed the Laboratory for Planetary Studies. In 1976, he was appointed the David Duncan Professor of Astronomy and Space Sciences, a named chair he held for the rest of his life. He lived in an Egyptian revival house perched on the edge of a cliff in Ithaca, drove a red Porsche 911 Targa, and kept a second orange 1970 Porsche 914 with the license plate PHOBOS, named for one of Mars's moons.

• 5. Pioneer, Voyager, and the Messages We Sent

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  Sagan assembled the first physical message ever launched from Earth into space: a gold-plated plaque attached to Pioneer 10, which lifted off in 1972. Pioneer 11 carried a copy the following year. He kept refining the idea.

  In 1977, he contributed to the Voyager Golden Record, a disc sent with the Voyager probes containing samples of the sights and sounds of Earth. Among much else, it features music by Bach, Beethoven, and Chuck Berry. The record was designed as a universal message, something that could potentially be understood by any intelligence that might eventually find it.

  Sagan also proposed the Pale Blue Dot photograph, the image of Earth taken by Voyager 1 from the outer reaches of the solar system, a pale speck of light suspended in a sunbeam. He later wrote a book using that title and image as its organizing metaphor.

  His scientific contributions to planetary exploration went further than designing messages. He was among the first scientists to hypothesize that Saturn's moon Titan might hold oceans of liquid compounds on its surface and that Jupiter's moon Europa might hide subsurface oceans of water. The spacecraft Galileo later provided indirect confirmation of Europa's ocean. He also investigated the mysterious reddish haze on Titan, which turned out to be complex organic molecules constantly raining down onto its surface.

  Sagan's work on Venus stretched back to his doctoral years. In the early 1960s, the surface conditions of Venus remained unknown. He analyzed radio emissions from the planet and concluded its surface temperature was around 500 degrees Celsius. Mariner 2 confirmed his conclusions in 1962. He went further, arguing that Venus had been transformed by a runaway greenhouse effect and testified to the United States Congress in 1985 that a similar process posed a growing danger to Earth.

• 6. Cosmos and the Art of Explanation

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  Sagan and his partner Ann Druyan co-wrote the thirteen-part PBS documentary Cosmos: A Personal Voyage, which aired in 1980. By the time Ken Burns's The Civil War surpassed it in 1990, Cosmos was the most widely watched series in the history of American public television. At least 500 million people across 60 countries saw it. It won two Emmy Awards and a Peabody Award.

  One contemporary reviewer, Frederic Golden, wrote that Sagan "roves through two millennia of scientific progress, often shuttling back and forth over the centuries like some Wellsian time traveler," appearing one moment in a cafe on the Greek island of Samos and the next in Cambridge's Cavendish Laboratories. The production recreated the Library of Alexandria. It featured music by Bach, Vivaldi, and Vangelis.

  The companion book became the bestselling science book to date. Author James Michener wrote that Sagan was "always readable, and because his mind ranges so far and wide, he seems exactly the right man for the job." Sagan's argument throughout Cosmos was that "We are a way for the cosmos to know itself."

  He had an explicit theory of why scientists should explain themselves to the public. He gave two reasons: the public funds much of science and deserves to know how the money is spent, and the joy of sharing excitement about discovery is reason enough on its own. He named the scientists he most admired in this role: Stephen Jay Gould, E.O. Wilson, Lewis Thomas, and Richard Dawkins in biology; Steven Weinberg, Alan Lightman, and Kip Thorne in physics; Roald Hoffmann in chemistry.

  His penultimate book, The Demon-Haunted World, extended this project into direct advocacy for critical thinking. He proposed what he called a "Baloney Detection Kit," a phrase coined by his wife's friend Arthur Felberbaum, offering tools to evaluate claims and resist pseudoscience. He also taught a Senior Seminar on critical thinking at Cornell, working the same material into the classroom.

• 7. Nuclear Winter and Political Courage

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  In 1983, Sagan was one of five authors, the "S" in what became known as the TTAPS model, who published the first scientific paper to use the phrase "nuclear winter," a term his colleague Richard P. Turco had coined. The paper modeled the catastrophic atmospheric effects of a large nuclear exchange: cooling, darkness, and disruption of agriculture severe enough to threaten civilization.

  The reaction from parts of the scientific community was sharp. Nuclear physicist Edward Teller began a personal correspondence with Sagan around 1983, initially expressing support for continued research. That exchange ultimately led Teller to write that a propagandist is someone who uses incomplete information for maximum persuasion, and that he could compliment Sagan on being an "excellent propagandist." Sagan's biographers later described nuclear winter as a low point for his scientific reputation, even as it raised his public profile.

  He did not retreat. In March 1983, when President Ronald Reagan announced the Strategic Defense Initiative, a project to build a comprehensive missile defense system quickly dubbed "Star Wars," Sagan joined other scientists in opposing it. He argued it was technically impossible to achieve the necessary perfection, far more expensive to build than for an adversary to defeat, and that its construction would destabilize the balance between the United States and the Soviet Union.

  When Soviet leader Mikhail Gorbachev declared a unilateral moratorium on nuclear weapons testing beginning on the 6th of August, 1985, the 40th anniversary of the Hiroshima bombing, the Reagan administration dismissed it as propaganda. Beginning on Easter Sunday in 1986 and continuing through 1987, peace activists staged protests at the Nevada Test Site. Sagan was arrested on two separate occasions as he climbed over a chain-link fence at the site during the underground Operation Charioteer and Musketeer nuclear test series.

  His concern about nuclear weapons tied directly to his thinking about extraterrestrial civilizations. He believed the Drake equation implied that many civilizations had formed across the galaxy, but the absence of any detectable signal, the Fermi paradox, suggested that technological species tend to destroy themselves. He hoped that recognizing this pattern might motivate humanity to survive it.

• 8. Skeptic, Science Fiction Fan, and the Last Years

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  Sagan credited two books with teaching him critical thinking early in life: Martin Gardner's Fads and Fallacies in the Name of Science and Charles Mackay's Extraordinary Popular Delusions and the Madness of Crowds. In 1974, he challenged Immanuel Velikovsky to a public debate. He wrote a column for Parade magazine proposing what he called a "Baloney Detection Kit." He lamented that most newspapers ran daily astrology columns while publishing almost no astronomy.

  His most famous statement, "extraordinary claims require extraordinary evidence," drew on a nearly identical formulation by fellow skeptic Marcello Truzzi and traced further back to the French mathematician and astronomer Pierre-Simon Laplace, who wrote in the 19th century that the weight of evidence should be proportioned to the strangeness of the facts.

  Science fiction never left him. He told interviewers it had led him to science in the first place. He was acquainted with science fiction fandom through his friendship with Isaac Asimov, who described Sagan as one of only two people he had ever met whose intellect surpassed his own, the other being computer scientist Marvin Minsky. Sagan briefly advised Stanley Kubrick on 2001: A Space Odyssey, suggesting the film imply rather than depict alien superintelligence.

  His own novel, Contact, required a way for its heroine to travel from Earth to the star Vega. Sagan asked his friend the physicist Kip Thorne for advice on wormhole physics, and that consultation led Thorne to original research on closed timelike curves.

  In 1993, engineers at Apple Computer code-named the Power Macintosh 7100 "Carl Sagan" as an internal joke about making billions and billions of dollars. Sagan sent a cease-and-desist letter. Apple complied but internally renamed the machine "BHA," standing for "Butt-Head Astronomer." After further legal proceedings, an out-of-court settlement was reached in November 1995.

  After developing myelodysplasia and receiving three bone marrow transplants from his sister, Sagan died of pneumonia at the Fred Hutchinson Cancer Research Center in Seattle on the 20th of December, 1996. He was buried at Lake View Cemetery in Ithaca. His papers, comprising 595,000 items, are now archived in the Library of Congress. In 2022, he was posthumously awarded the Future of Life Award for his role in developing and popularizing the science of nuclear winter, an honor accepted by his widow Ann Druyan.