After swinging by Jupiter, Saturn, Uranus and Neptune and shooting spectacular pictures of the planets and their moons, the U.S. spacecraft Voyager 2 had by 1990 completed its Grand Tour of the planets and was speeding out into deep space on its way to the stars. But the temptation of one last backward look was irresistible. Swinging its camera around, it took snapshots of the now distant planets as they might appear to an alien craft approaching the solar system.
And there was Earth, barely discernible against the background of stars, an image that inspired the title of The Pale Blue Dot (Random House; 429 pages; $35), the ninth book by astronomer and planetary scientist Carl Sagan. Voyager's homeward glance was his idea, and the sight was humbling. "There is perhaps no better a demonstration of the folly of human conceits," he writes, "than this distant image of our tiny world." To say nothing of the folly of wars, which from space would appear to be little more than "the squabbles of mites on a plum."
Having placed the Earth in proper perspective, Sagan launches his own Grand Tour of just about everything in space that surrounds it. Elegantly and appealingly, he surveys the current state of knowledge about the solar system, nearby stars, distant galaxies and even the very edge of the universe. As he describes each heavenly body or cosmic phenomenon, the author imparts a healthy dose of science, making it palatable to the lay reader by using jargon-free English buoyed by emotion and humor.
Sagan traces the history of space flight and looks ahead to the time when humans will fly from a dying or imperiled Earth to other worlds, "terraforming" them to make them livable and inhabiting them to preserve the species. Sagan writes that space flight has already provided early warnings of possible dangers to Earth. Data radioed from craft exploring Venus and Mars, for example, have helped make us aware of the consequences of such potential man-made disasters as the greenhouse effect and the destruction of the ozone layer. Perhaps even more important, spacecraft may one day prevent a global catastrophe by diverting a large asteroid speeding toward a collision with Earth.
It is Sagan's optimistic vision, however, rather than any foreboding of apocalypse, that shines through every chapter of this handsomely illustrated ^ book. Anticipating human exploration of Mars, for example, Sagan foresees a Jeep-like vehicle carrying astronauts on the lookout "for rocks from ages past, signs of ancient cataclysms, clues to climate change, strange chemistries, fossils or -- most exciting and most unlikely -- something alive. Their discoveries are televised back to Earth at the speed of light. Snuggled up in bed with the kids, you explore the ancient riverbeds of Mars."