Carl Sagan's worldview spanned beyond the cosmos and its scientific glory. In fact, many view him as a leader of the skeptic movement and famous critical thinker.
Sagan made popular "the idea that really you can use scientific-type reasoning in all sorts of walks of life," says William Poundstone, who wrote a biography on Sagan. "Everything from politics to health, to the actual beliefs and superstitions that we all have." It's something he's admired for.
The famous scientist and author was particularly outspoken about the nuclear arms race and Cold War between the United States and the Soviet Union. Sagan lobbied to reduce nuclear arms and warned of the potential dangers humanity could bring upon itself. His nuclear winter theory gained public attention and grew out of his earlier planetary science studies. He speculated that a barrage of nuclear explosions would churn up so much dust that it would interfere with the Earth's climate. People surviving the explosions would be doomed if enough dust blocked the sunlight needed to grow crops. Sagan's scenario may hold some truth, but it also has its critics [source: Poundstone]. Either way, Sagan highlighted the fact that there could be unintended consequences from nuclear war.
Ann Druyan, Sagan's wife, describes him as a "scientist through and through." Sagan's religious views stemmed from his emphasis on evidence and truth -- two pursuits that ruled out traditional worldviews of God to him. Contrary to other labels, Druyan says Sagan identified himself as agnostic, not atheist -- he didn't believe in religions and tried to not belittle them. But this didn't mean he wasn't a spiritual person, she said.
After being diagnosed with a rare bone marrow disease in 1994, Sagan weighed his options and sought the best treatment in Seattle, Wash. Treatment would likely involve a bone marrow transplant -- Sagan's sister, whom he was never too close with, volunteered to partake in the procedure [source: Poundstone].
But Sagan didn't get entirely better. More than a year and a half after the transplant, he became sick from an infection. On Dec. 20 1996, Sagan, then 64, succumbed to his illness.
Druyan says Sagan's legacy lives on. Shortly following his death, she and others help finish the movie based on his book "Contact." It was bittersweet, she said.
At the end of the film, "For Carl" appears on the screen.