[In Cosmos Carl Sagan] is an enormously gifted juggler, at one time keeping aloft a dizzying melange of balls, dishes, Indian clubs, dinosaurs, and Dopplered red shifts. His ability to explain the complex in terms of the commonplace is mesmerizing; his encyclopedic knowledge is humbling; his articulateness captivates. His staff of illustrators and technicians is skilled and inventive. On camera or in print, Dr. Sagan is artfully at ease with the arcane and his love affair with the cosmos is infectious. He is an irresistibly stimulating teacher.

And there's the rub.

Dr. Sagan and the televised "Cosmos" series reached a vast audience. He intrigued adults, who since college have had to leave behind pondering the ponderous and concentrate on the more pedestrian process of making a living. And he fascinated young students, especially very intelligent students, who still have the leisure and curiosity to ask what living is...