The monorail was losing speed as it climbed up out of the shadowed lowlands. At any moment now, thought Sadler, they would overtake the sun. The line of darkness moved so slowly here that, with a little effort, a man could keep abreast of it, could hold the sun balanced on the horizon until he had to pause for rest. Even then, it would slip so reluctantly from sight that more than an hour would pass before the last dazzling segment vanished below the edge of the Moon, and the long lunar night began.

He had been racing through that night, across the land that the first pioneers had opened up two centuries ago, at a steady and comfortable five hundred kilometers an hour. Apart from a bored conductor, who seemed to have nothing to do but produce cups of coffee on request, the only other occupants of the car were four astronomers from the Observatory. They had nodded affably enough when he came aboard, but had promptly lost themselves in a technical argument and had ignored Sadler ever since. He felt a little hurt by this neglect, then consoled himself with the thought that perhaps they took him for a seasoned resident, not a newcomer on his first assignment to the Moon.

The lights in the car made it impossible to see much of the darkened land through which they were racing in almost complete silence. “Darkened,” of course, was only a relative term. It was true that the sun had gone, but not far from the zenith the Earth was approaching its first quarter. It would grow steadily until at lunar midnight, a week from now, it would be a blinding disk too bright for the unprotected eye to gaze upon.

Sadler left his seat and went forward, past the still-arguing astronomers, toward the curtained alcove at the front of the car. He was not yet accustomed to possessing only a sixth of his normal weight, and moved with exaggerated caution through the narrow corridor between the toilets and the little control room.