Carl Sagan warmed the universe.

His cosmos was not cold and dark and impenetrable. He believed the universe was surely filled with life, intelligent life, innumerable civilizations unseen. In his younger, dreamier days, he thought advanced extraterrestrials might know how to cruise the galaxies in ramjets -- spaceships with massive openings that scoop up hydrogen atoms from interstellar dust clouds and use them for fuel. In Sagan's crowded cosmos, even empty space wasn't empty.

He told The Washington Post earlier this year: "Organic matter, the stuff of life, is absolutely everywhere. Comets are made one-quarter of organic matter. Many worlds in the outer solar system are coated with dark organic matter. On Titan, organic matter is falling from the skies like manna from Heaven. The cold diffuse interstellar gas is loaded with organic matter. There doesn't seem to be an impediment about the stuff of life."

The world needed Sagan, who died yesterday of pneumonia at the age of 62. We have needed Sagan ever since Copernicus removed us from the center of the universe. It is a perplexing fact of human life that we live on a rock that orbits an ordinary star on the outskirts of an ordinary galaxy in a universe that is indescribably large. Sagan knew how to describe it, to convey our humble position without demeaning us. With Sagan we felt in the right place.

Humans were not small and irrelevant things in the Sagan doctrine. For all his talk of space and stars and galaxies, his most consuming interest may have been human beings. He won the Pulitzer Prize not for his book "Cosmos" but for "The Dragons of Eden," about the evolution of human intelligence. He was unhesitant to dive into the political arena, an unabashed liberal, warning that a nuclear war would lead to a "nuclear winter." His most recent book, "The Demon-Haunted World," was an attack on superstition and pseudoscience, from the UFO craze to the excesses of the recovered-memory movement.

It's difficult to pay tribute to all of Sagan's achievements, because they were ridiculously many (his resume prints out to 250 pages) and because one suspects that Sagan could have said it all better. That was his ultimate gift. Yes, he was smart -- his colleagues often said Sagan was the smartest person they knew -- but what set him apart, and promises to make him remembered long into the future, was his uncanny ability to communicate. He never suffered the disease of jargon. His 13-part series "Cosmos" was remarkable not only for introducing millions of Americans to astronomy, but also because its host was a real astronomer, someone who helped discover that Venus was broiling hot and that giant dust storms raged across the face of Mars.

Earlier this year he told this reporter, "I've been fantastically lucky."

I had tried to get him to admit to some resentments. Sagan had taken plenty of knocks. He had been mocked and parodied. The millions of words he had written had been boiled down to three in the public imagination: "billions and billions" (which, he says, he never actually said. He'd even reviewed the "Cosmos" tapes to make sure).

Sagan made some mistakes, reached too far, pushed himself into realms in which he may have lacked expertise. Some colleagues dismissed him as a "popularizer," as though this was a crime. He was turned down for membership in the National Academy of Sciences after an unusual debate. Never mind his work on Venus and Mars; a serious scientist is not supposed to go on "The Tonight Show."

But Sagan betrayed no bitterness: "I've gotten so much more than my fair share of honors and recognition," he said.

Eventually the academy gave Sagan a special award for his educational efforts. It wasn't quite the same as accepting him as a member. Science as an industry owed more to Sagan. He not only could explain complex information in a simple way, he could imbue his material with joy, beauty, a sense of meaning. Too often modern science declares the world to be pointless, to be a random aggregation of freak accidents and mathematical principles.

Sagan said, "Everybody starts out as a scientist." Every child has the scientist's sense of wonder and awe. Too often we beat it out of the kid. "The job of a science popularizer," Sagan said, "is to penetrate through the teachings that tell people they're too stupid to understand science."

He died before he could achieve his lifelong dream of making contact with some extraterrestrial civilization. But he also knew the joy and excitement of being close to finding life itself. Seriously ill, he had closely followed the saga of the Mars rock, with its possible ancient Martian microbes. To the end he was optimistic. He felt he would live, that he had rounded the corner on the bone marrow disease that had struck him two years ago.

In his book "Pale Blue Dot," he warns that someday the sun will heat up, the atmosphere of the Earth will dissipate to space, the ground will roast, the oceans boil. He said we should find a way someday to leave the solar system, travel among the stars, keep our species alive. Sagan believed that humans are special, noble, a piece of the cosmos too important to become extinct.

Among members of that species he was surely one of the finer specimens. CAPTION: Carl Sagan, conveying universal truths in a down-to-earth way. CAPTION: Carl Sagan not only explained complex information simply but imbued it with beauty.