When I think about Carl Sagan, the tenth anniversary of whose death we remember today, the first thing that comes to mind is a quote about the wonders of relativistic interstellar flight. It’s worth quoting at length:

If for some reason we were to desire a two-way communication with the inhabitants of some nearby galaxy, we might try the transmission of electromagnetic signals, or perhaps even the launching of an automatic probe vehicle. With either method, the elapsed transit time to the galaxy would be several millions of years at least. By that time in our future, there may be no civilization left on Earth to continue the dialogue. But if relativistic interstellar spaceflight were used for such a mission, the crew would arrive at the galaxy in question after about 30 years in transit, able not only to sing the songs of distant Earth, but to provide an opportunity for cosmic discourse with inhabitants of a certainly unique and possibly vanished civilization. Despite the dangers of the passage and the length of the voyage, I have no doubt that qualified crew for such missions could be mustered. Shorter, round-trip journeys to destinations within our Galaxy might prove even more attractive. Not only would the crews voyage to a distant world, but they would return in the distant future of their own world, an adventure and a challenge certainly difficult to duplicate.

That’s from Intelligent Life in the Universe, which Sagan and Iosef Shklovskii published in 1966 (Holden-Day, pp. 443-444). It’s actually a translation and extended revision of Shklovskii’s older Universe, Life Mind, and the quote draws on a 1963 Sagan paper called “Direct Contact Among Galactic Civilizations by Relativistic Interstellar Flight” (Planetary and Space Science 11, pp. 485-98). Sagan had sent Shklovskii the paper even before the latter’s book appeared. The result in English became a collaborative effort that drew on the wisdom of two outstanding minds.

I don’t know how many space scientists were fired by this vision of human voyaging not just to another star but another galaxy, but I suspect this book still sits on the shelf of many a researcher. It awoke in me the sense of awe that Poul Anderson would go on to tap in Tau Zero, his fine novel about a runaway starship that makes Sagan’s 30-year voyages to Andromeda seem tame by comparison. But that’s what Sagan did. He could render hard science into celestial mental voyaging.

Good scientists do that in their own minds. Sagan’s genius was the ability to convey it to a broad audience, using prose that was supple and keen as a knife-edge. The great mystery writer Ross Macdonald once said of Raymond Chandler that he wrote ‘like a slumming angel.’ It’s the perfect phrase for Sagan as well, whose voice was distinctive and marked by a preternatural clarity. When Cosmos widened his reach to television, he was able to bring the discoveries of our telescopes and spacecraft into the home and (with a kind of poetry) show us where we stood in the universe.

Pale Blue Dot (1994) was Sagan at his best as he ranged through the Solar System and looked back on a distant Earth. Here’s the memorable conclusion:

The Cosmos extends, for all practical purposes, forever. After a brief sedentary hiatus, we are resuming our ancient nomadic way of life. Our remote descendants, safely arrayed on many worlds through the Solar System and beyond, will be unified by their common heritage, by their regard for their home planet, and by the knowledge that, whatever other life may be, the only humans in all the Universe come from Earth.

They will gaze up and strain to find the pale blue dot in their skies. They will love it no less for its obscurity and fragility. They will marvel at how vulnerable the repository of all our potential once was, how perilous our infancy, how humble our beginnings, how many rivers we had to cross before we found our way.

A slumming angel indeed. Thank you, sir.

Note: As Larry Klaes just pointed out in a comment to this post, Joel Schlosberg is conducting an ongoing Sagan tribute centered on this day, and Larry also notes the Celebrating Sagan weblog in his honor. Larry’s own tribute to Sagan in the Ithaca Times is here. Music of the Spheres has a fine recollection as well. Be sure to read Airminded’s homage, and finally, check Ann Druyan’s thoughts about her late husband.