CARL SAGAN

It’s been a long 10 years since we’ve heard Carl Sagan beckoning us to consider the possibilities inherent in the “billions” of stars peppering the sky and in the “billions” of neuronal connections spiderwebbing our brains.

In the day, the Cornell astronomer, Pulitzer Prize-winning author of books like “The Dragons of Eden,” “Contact,” “Pale Blue Dot” and “The Demon-Haunted World,” impresario of the PBS program “Cosmos” and Johnny Carson regular was one of the world’s most famous and eloquent unbelievers, an apostle of cosmic wonder, critic of nuclear arms and a champion of science’s duty to probe and question without limit, including the claims of religion. He died of pneumonia after a series of bone marrow transplants in December 1996.

In his absence, the public discourse on his favorite issues — the fate of the planet, the beauty and mystery of the cosmos — has not fared well. The teaching of evolution in public schools has become a bitter bone of contention; NASA tried to abandon the Hubble Space Telescope and censor talk of climate change; and of course, religious fanatics crashed jetliners into the World Trade Center, leading to a war in the Middle East that has awakened memories in some corners of the Crusades.

Now, however, Dr. Sagan has rejoined the cosmic debate from the grave. The occasion is the publication last month of “The Varieties of Scientific Experience: A Personal View of the Search for God” (Penguin). The book is based on a series of lectures exploring the boundary between science and religion that Dr. Sagan gave in Glasgow in 1985, and it was edited by Ann Druyan, his widow and collaborator.

Reading Dr. Sagan’s new book is like running into an old friend at a noisy party, discovering he still has all his hair, and repairing to the den for a quiet, congenial drink.

“I would suggest that science is, at least in part, informed worship,” he writes at the beginning of a discussion that includes the history of cosmology, a travel guide to the solar system, the reason there are hallucinogen receptors in the brain, and the meaning of the potential discovery — or lack thereof — of extraterrestrial intelligence.

Never afraid to venture into global politics, Dr. Sagan warns at one point of the danger that a leader under the sway of religious fundamentalism might not try too hard to avoid nuclear Armageddon, reasoning that it was God’s plan.