Astronomer Carl Sagan in 1981 as he was getting ready for his television series, Cosmos. (Eduardo Castaneda/AP)

Carl Sagan died 20 years ago Tuesday, at the far-too-young age of 62. He had many strong beliefs, none greater than his conviction that science was a candle in the dark.

There’s a lot of darkness these days — science denialism in its various forms. It’s certainly not a novel development, but it’s a bigger problem than ever given the scale of our scientific and technological challenges. The world has 7 billion of us now, and we need to be smart and correct and wise. We need to be wary of bunk. Technologies that spread knowledge also spread nonsense and abet charlatans. When Sagan died, the World Wide Web was only a few years old, search engines were just getting going, and social media and smart phones were a decade in the future. Climate change was already a big topic, one that incited anti-scientific arguments, but the issue had not yet become completely and hopelessly politicized. The Lancet had not yet published a notorious anti-vaccine study that would later be retracted.

The list of scientifically mediated, politically divisive issues is a long one, and Sagan would have been a busy man these last 20 years.

Two decades after his death, we still haven’t found any extraterrestrial life — and Sagan, who always hoped for such discovery, probably would be surprised by that. SETI has detected no persuasive evidence of distant intelligence. The subject of a book Sagan co-authored, “Intelligent Life in the Universe,” remains speculative half a century later. The hard evidence didn’t materialize in his lifetime and hasn’t yet surfaced in ours, although there have been tantalizing signs, hints, possibilities. That’s not good enough. Science sets high standards, and Sagan liked to say that extraordinary claims require extraordinary evidence.

But look what has been discovered since he left us. Then, only a handful of stars were known to have planets. Now we know that planets are everywhere, that they’re a common feature of star formation and that Earth-sized planets exist in great abundance. When Sagan died, the age of the universe was still uncertain. We now know it is 13.82 billion years old. (Cosmology is getting so precise we will probably learn at some point that the universe began on a Thursday.) We now know that the universe is accelerating in its expansion due to “dark energy.” We now know that Einstein was right when he predicted the existence of gravitational waves. (But did we ever really doubt him?)

We’ve seen Pluto up close. There may be another big planet lurking in the outer solar system. Rovers are rolling on Mars, which we now know was once warm and wet.

What would Sagan be most excited about? Maybe this new era of gene editing. What’s going to happen with CRISPR? What kind of world are we creating? The world still needs people who can explain stuff — and so it misses Carl Sagan.

Read more:

From 1996: My Style section profile of Sagan

Carl Sagan denied being an atheist. So what did he believe?

The heroes and the secrets of the Pluto mission

Smithsonian article on Sagan