This video is made possible by Brilliant. You’re going to learn more about Brilliant later in today’s video, but if you’d like to learn more about them right now, go to brilliant.org/bargraphics. You’ll also find a link in the description below.

If you were alive during the 80s and 90s, there’s likely a single name you associate with the word “science”: Carl Sagan. He was the most popular scientist of his era, a trained astrophysicist who worked on some of NASA’s most famous missions. Sagan was the man who turned a generation onto the wonders of our solar system. While most of us probably only know Sagan’s public persona from PBS’s classic 1980 series “Cosmos,” how many of us know the man himself?

Born on November 9, 1931, in Brooklyn, Carl was a boy with plenty of time on his hands for thinking. His father, Samuel, worked long hours in the garment industry, while his mother, Rachel, was strongly religious and active in the local Reformed Jewish community. As a result, young Carl spent many hours left to his own devices, trying to find answers to a seemingly simple question: What were the stars that he could see?

Finding out the truth was harder than it sounded. According to Sagan, most of the adults he asked would reply with things like, “They’re just lights in the sky.” But the boy knew they had to be something more. What were these lights? What were they made of? How did they get there? The answer to that question would change young Carl’s life.

Sent by his mother to the New York Public Library at either age 5 or 7 (the number changes depending on who is telling the story), the boy asked for a book on the stars. In an oft-told tale, Sagan would later recount how the librarian initially gave him a book on Clark Gable and Greta Garbo. Eventually, though, the boy got his book on astronomy. Back in Brooklyn, he sat down to find the answer to his question: “The Sun,” the book said, “is a star.” But close-up, the stars are suns, just far away. For the young boy from Brooklyn, it was a revelation. Those lights in the sky were other suns, each possibly circled by their own worlds, each shining down on some alien city where another boy looked at the heavens and wondered what those lights were.

In that moment, Carl’s conception of the universe expanded. The discovery turned the boy into a veritable science fiction nut. He devoured the Martian novels of Edgar Rice Burroughs and began plotting to get himself abducted by aliens. In 1945, when he heard of Hitler’s V2 rockets falling on England, the boy thought only of how he could take one of those rockets and ride it to another world. In 1947, Samuel Sagan was making enough money to move his family out of New York and into a middle-class neighborhood. By now, young Carl was 13 and obsessed with UFOs.

It’s easy to imagine that this biography could turn into that of a great science fiction writer. Carl made his first-ever radio broadcast around this time, telling audiences of a local college station that aliens were visiting Earth. It wouldn’t be fiction that supplied Carl an outlet for his feelings of awe about space. In 1951, after graduating high school, Carl enrolled at the University of Chicago to study physics. It was while there that Sagan came to the attention of Gerard Kuiper, the man for whom the Kuiper Belt on the fringes of our solar system is named. Kuiper is known today as the father of planetary science, and he was about to transform young Carl Sagan into his protégé.

On October 5, 1957, a strange speck of light streaked through the skies above Earth. If any children looked up and asked their parents what that light was, they wouldn’t have gotten the answer that Carl Sagan once had: this wasn’t a star; it was Sputnik 1, the first man-made satellite ever put into space, and it was about to kick off the space race. For Sagan, the flight of Sputnik 1 was the capstone to an eventful year. That June, he had married Lynn Alexander, and the two were already planning to start a family. At the same time, his PhD advisor, Gerard Kuiper, was getting Sagan extra credit work on a top-secret U.S. government project to detonate a nuclear bomb on the moon.

Sagan was being pulled toward planetary science, and the planet that eventually captured him was Venus. This was not a clever metaphor for love; the actual planet Venus was the focus of Sagan’s thesis, in part because it was still such a mystery. At the end of the 1950s, all scientists knew about Venus was that it was covered in clouds. Many still assumed rolling oceans or maybe even humid jungles lay below the atmosphere. Sagan theorized that Venus was a hellish planet with an atmosphere hot enough to melt lead. Not long after, it was proven right.

Barely had he graduated in 1960 when he was snapped up by the University of California, Berkeley, to help build instruments for NASA’s Mariner 2 mission. Two years later, he was poached to work at Harvard University and the Smithsonian Astrophysical Observatory. It was while at Harvard that Sagan identified Mars’s epic swirling dust storms. He also got seriously into aliens. For all his reputation, Sagan was at heart still a kid fantasizing about life on Mars.

As the 1960s got underway, Sagan began writing books on the existence of aliens and got involved with SETI, the Search for Extraterrestrial Intelligence. Around this time, Sagan’s personal life was tumultuous. He divorced Lynn Alexander in 1962 and watched as she took the kids away. Four years later, on April 6, 1986, he married the artist Linda Salzman. That same year, he changed jobs again. His fascination with aliens had made the planetary scientist something of an embarrassment to Harvard, so it was with mutual relief that Sagan applied for a job at Cornell, working alongside his new SETI buddy Frank Drake at the Laboratory for Planetary Studies.

Sagan kept up his work with NASA, becoming part of the briefing team for the Apollo 11 crew. A year later, he finally laid out his views on aliens at a UFO symposium. The scientists argued that intelligent life in our galaxy was a very real possibility, but Sagan also argued against the idea that aliens were visiting Earth in UFOs and probing farmers. It was an important distinction that set Sagan apart from those obsessed with Roswell.

By 1971, Sagan was a full professor at Cornell, with a nice side line in briefing reporters on complex scientific topics. His natural charisma and ability to condense complicated ideas into easy-to-understand analogies made him a darling of the serious press. But if Sagan’s fellow scientists were already fed up with his celebrity, they were about to get even more frustrated.

In 1971, NASA was deep in the final preparation stages for the Pioneer 10 and 11 probes, the most ambitious space mission to date. The twin pioneers were designed to become the first man-made objects to pass through the asteroid belt and investigate the outer planets. But it was another detail about the pioneers that really captured the public’s attention: after they completed their missions, they would carry on out into interstellar space. If aliens were monitoring our solar system’s fringes, Pioneer 10 would be the first man-made object they ever encountered.

Most serious scientists paid little attention to this aspect of Pioneer, but the idea captured Carl Sagan’s imagination. If an alien civilization picked up the probe, what would they think? Sagan’s big breakthrough was realizing that we could tell them what to think. Months before the Pioneers launched, Sagan contacted NASA and told them he wanted to affix a plaque to each Pioneer case. To his infinite surprise, NASA basically said, “Sure, why not?”

In 1971, Sagan, his wife Linda, and Frank Drake sat down to write a message to the universe. Today, the Pioneer plaque is iconic, but even if you’ve seen it, you might not be aware of how detailed it is. The basic idea was to show aliens who we are and where we come from. The first part was easy: the plaque has an engraving of a naked man and a woman facing outwards. The second part was much more challenging: how do you demonstrate ideas of distance to a totally alien intelligence that has no conception of feet or meters?

Sagan’s team hit upon the idea of using a hydrogen atom, the most common element in the universe. Hydrogen atoms can exist in different energy states, and when they change states, they release a wave of electromagnetic radiation. Sagan, Drake, and Linda turned this wave into a universal measurement. The length is around 21 centimeters, the distance light travels in about 0.7 of a nanosecond. They then used this measurement to describe everything from the average height of humans to the distance to Earth.

The plaque is a masterpiece of science and art joined hand in hand, but it’s also monumentally useless. Although Pioneer 10 is aiming in the vague direction of another star, Aldebaran, the chances of either probe ever encountering intelligent life are so close to zero that you might as well just say zero. People in 1971 were all too aware of this and were outraged that Sagan had spent millions of taxpayer dollars on a picture that would never even be seen. Yet Sagan maintained that it was the right thing to do. He wasn’t building that plaque for aliens; he was building it for us here on Earth. He wanted to show the public not just what humanity could do but how big and wonderful the universe they lived in was.

In 1972, Pioneer was launched, followed shortly after by Pioneer 11. Today, both probes are still out there, carrying Sagan’s plaque towards the very edges of our solar system. Back on Earth, the Pioneer plaque made Sagan an international celebrity, but his personal publicist wasn’t done yet; his greatest achievements were just around the corner.

In 1977, NASA was preparing to launch two Voyager probes towards Jupiter and Saturn, which would then carry on into interstellar space. Buoyed by the PR the Pioneer plaque had generated, the agency contacted Sagan with a much bigger proposal: they wanted to send a literal record of humanity into space for aliens to one day find. NASA wanted Sagan to decide what would go on it.

The Voyager Golden Record is today iconic, but in 1977, it was a head-scratching challenge. Pressing a record and encoding it with instructions would be hard enough, but the real challenge would be choosing what to put on it to represent humanity. Sagan assembled a team consisting of himself, his wife Linda, Frank Drake, and the artist John Lombardi, as well as Timothy Ferriss, contributing editor at Rolling Stone.

For the next few months, the team worked tirelessly to cram as much information onto the record as possible. This included samples of human heartbeats, greetings read out in 55 different languages, whale songs, and the whole of Chuck Berry’s “Johnny B. Goode.” It also included a handful of analog pictures, some obvious ones like the Taj Mahal and the Golden Gate Bridge, as well as more scientific ones like DNA structures and images explaining human processes of eating and drinking.

But the most interesting was a scan of the author Anne Druyan’s brainwaves during the recording process. The team reasoned that a super-advanced alien society could probably decode those brainwaves. Druyan was given strict instructions to think of certain common objects while her brain was scanned for an hour. It was only much later, after Voyager 1 and Voyager 2 were well on their way out of the solar system, that Druyan admitted she hadn’t followed those instructions. She and Sagan had started an affair, and her recording was full of thoughts of the man she had just fallen for.

Voyager 2 launched on August 20, 1977, and Voyager 1 followed on September 5. Sagan described them eloquently as a message in a bottle cast into the cosmic sea. Thirty-five years later, in 2012, Voyager 1 became the first man-made object to enter interstellar space. Although Voyager 2 has since joined it, as of November 2018, Voyager 1 remains the farthest man-made object from Earth.

Not long after the probes were launched, Sagan and Druyan started looking for a reason to continue working together. That same year, they hit on the perfect idea: they would write a TV show about science, one that condensed the whole amazing history of human achievement into 13 hour-long thought-provoking episodes. The name of that show? “Cosmos.”

For millions of people, their defining image of Carl Sagan will forever be the scientist standing on the edge of a low cliff before a pounding sea, describing the impossible extent of our universe. The first episode of “Cosmos” aired on September 28, 1980, three years after Sagan and Druyan first sat down to start writing. These had not been easy years; Sagan was going through a very acrimonious divorce from Linda Salzman, and in 1979, Sagan’s father, Samuel, was diagnosed with cancer. The onset was swift and shocking, forcing Samuel and Rachel to move in with Sagan. For months, Sagan watched his father dying, unable to tear himself away from his work on “Cosmos” and Cornell long enough to give his father the goodbye he deserved.

When Samuel finally passed away in October 1979, Sagan was devastated. Yet life must go on, and for Carl Sagan, that meant finishing “Cosmos.” For PBS, American Public Television has never created anything as popular since. It’s estimated that half a billion people watched “Cosmos” globally on transmission. What’s striking today is how captivating it remains. While the retro 80s graphics are amusing in hindsight, Sagan’s earnestness still shines through. His sense of wonder is still enough to inspire anyone to dedicate their life to science.

However, it wasn’t a perfect show by any stretch. The endless shots of Sagan pulling up dandelions and gasping in awe at some computer graphics are almost enough to make you laugh. There’s a story that one of the producers was so annoyed by those shots that he stuck them into every episode just to make Sagan look silly. Unintentionally hilarious cutaways aside, “Cosmos” still managed to turn Sagan into a household name. Had he ended his career at this point, he probably would have been remembered warmly by just about everyone.

But Sagan didn’t stop there. Instead, he followed up “Cosmos” by getting seriously into activism. The turning point came in 1983, two years before Sagan finished divorcing Linda and married Druyan. That year, Sagan went into the hospital for a routine appendectomy and nearly died. He came so close to bleeding out that only a 10-hour emergency surgery saved his life. When Sagan recovered, he seemed changed by the experience. He no longer wanted to merely educate people about the world; he wanted to shape it for the better.

While still in the ICU, Sagan organized a mass protest against Ronald Reagan’s new Star Wars missile defense system, making him unpopular among Republicans. Sagan was horrified by U.S. nuclear brinkmanship with the Soviet Union and attempted to win over the public to his cause. In 1983, he co-authored a paper that introduced the concept of nuclear winter, the idea that even a limited nuclear exchange would cool the climate so drastically that famine would wipe out most of humanity. Around the same time, Sagan began campaigning against global warming, calling it a threat to mankind and demanding an international solution.

In 1986, he even managed to get himself arrested as an anti-nuclear activist in Nevada for trespassing on government property in an attempt to halt underground testing. Still, this was a minor brush with the law at best, and controversial or not, Sagan was still beloved by millions. He was only 52 and had decades left to win people over to his side.

On February 14, 1990, Voyager 1 turned its camera towards Earth for the final time. From unimaginable millions of miles away, the probe snapped a photo of our planet suspended in a sunbeam. The picture was the work of Carl Sagan, who had convinced NASA to turn Voyager 1 around for this one moment. When the image finally arrived back on Earth, it changed our conception of our planet. You’ve almost certainly seen the “Pale Blue Dot” photo before and felt that sense of awe, seeing everything you’ve ever known reduced to a tiny speck in the infinity of space.

But Sagan wasn’t content to simply be the driving force behind the image; he wanted the picture to make a statement that mankind could carry through the ages. It’s a statement worth quoting at length: “Look again at that dot. That’s here. That’s home. That’s us. Honest. Everyone you love, everyone you know, everyone you’ve