"Beacon?" Scyth nodded. "You have the insular viewpoint," he remarked. "You can stand at night and point out your destination. But you cannot even see Marandis from here, even with the finest telescope ever built. Stars lie in the way, huge gas fields and nebular clouds block fast direct passage. To chart our course safely past such stellar menaces, we establish beacons at the ends of certain free passages. For instance, Sol lies at the end of a fifteen hundred light year straightaway from the last beacon we set up. Here at Sol a slight turn in the course is made and there is another straightaway for a thousand light-years toward the Spiral Cluster. We--my friends and I--are charting the course through a rather interesting rift from Marandis to the Spiral Cluster. This rift, along which you lie, has been hidden from us for thousands of years. When it is finished it will cut hours from our travel-time." "And maybe so. But what is a beacon and how do you establish it?" "Dusty, when a spacecraft is running at fifteen hundred light-years per hour, a three-day-variable star winks in the sky ahead like a blinker-light." Scyth chopped his left palm rapidly with the edge of his right hand. "Wink-wink-wink it goes. And the pilot puts his spacecraft point-of-drive on the beacon and holds it there until he passes it and aims to the next. You--" "Variable star!" blurted Dusty. "Yes. The three-day variables are used for course markers; the longer variables are used to denote gas fields, nebular dust, and the like, and the still-longer beacons are used to denote places where various well-travelled starlanes meet, cross or merge. It is--" "Three day variable--" breathed Dusty. "Yes. In three days Sol will rise ten times its present brightness and fall again to less than one tenth of the present brightness. This is accomplished by creating an atomic instab--" "My God! How can any race live under such conditions?" "They cannot. Not unless properly prepared, well taken care of, aware and ready for it." "Look," snapped Dusty. "Why not go out and use some other star for your damned beacon?" Scyth shook his head. "If we were gods," he said quietly, "we could park the Galaxy on our desk, pick up a broom-straw and by fitting and trying we could locate the best course through the star-fields. But--" "If you were gods," grunted Dusty bitterly, "you could reach in and move a few stars aside and run your damned channel on a dead line from one end to the other. So why do you use Sol?" "Because the two straightaway lanes that meet at Sol do not meet at some other star. In one or two cases along this rift the original surveyors provided alternates in case we ran into trouble. But not on this one. No, Dusty, we cannot change our plans." "But see here--" "Dusty, you wouldn't stand in the way of Galactic Civilization, would you?" "You're damn well tootin' I would if it's going to mow me down if I don't."