No amount of standing on hilltops on dark nights and surveying the heavens could prepare a man for the actuality of space travel, because the earthbound observer saw only the the stars, not what separated them. They glittered in his vision, filling his eyes, and he had no choice but to assign them a position of importance in the cosmic scheme. The space traveler saw things differently. He was made aware that the universe consisted of emptiness, that the suns and nebulae were almost an irrelevancy, that the stars were nothing more than a whiff of gas diffusing into infinity. And sooner or later that knowledge began to hurt.