Sol, seen at a distance of sixteen light-years, is a little fainter than the star at the tip of Orion’s sword, and it could not have been contributing much to the sparkle in the diamond lenses of the strange machine. More than one of the watching men, however, got a distinct impression that the thing was taking a last look at the planetary system where it had been made. It would be a natural thing for any sentient and sentimental being to do, for it was already falling toward the great dark object only a few thousand miles away.

Any ordinary planet would have been glaringly bright at that range, for Altair is an excellent illuminator and was at its best right then: Altair is not a variable star, but it rotates fast enough to flatten itself considerably, and the “planet was in a part of its orbit where it got the maximum benefit from the hotter, brighter polar regions. In spite of this, the world’s great bulk was visible chiefly as a fuzzy blot not very much brighter than the Milky Way, which formed a background to it. It seemed as though the white glare of Altair were being sucked in and quenched, rather than illuminating anything.

But the eyes of the machine had been designed with Tenebra’s atmosphere in mind. Almost visibly the robot’s attention shifted, and the whitish lump of synthetic material turned slowly. The metal skeleton framing it kept pace with the motion, and a set of stubby cylinders lined themselves up with the direction of fall. Nothing visible emerged from them, for there was still too little atmosphere to glow at the impact of the ions, but the tons of metal and plastic altered their acceleration. The boosters were fighting the already fierce tug of a world nearly three times the diameter of distant Earth, and they fought well enough so that the patchwork fabrication which held them suffered no harm when atmosphere was finally reached.