vdB 14 and vdB 15: A Star to Measure By

"Kid, you want to know the difference between a pilot and a passenger? A pilot knows where he is without asking anybody." Chief Navigator Hollis Brandt leaned back from the plot tank of the freighter Margaret Kelly and jabbed a thumb at the forward screen. "Camelopardalis. Find me the Twins."

Cadet Ruiz found them, because she was not stupid, only nineteen. Two bright stars about half a degree apart, each wrapped in its own smear of dust. "CS Cam and CE Cam," she recited. "Blue supergiants, a bit over three thousand light-years out, about nineteen solar masses apiece. They light the reflection nebulae vdB 14 and vdB 15, in the Cam OB1 association. Chief, they're in every textbook. Why learn them by eye when the computer knows them to six decimal places?"

Brandt grinned the grin of a man who had been waiting all watch for exactly that question. "Because the computer learned them from somebody. Look at CE, the one in the pinker cloud. Back in 1943 three astronomers at Yerkes sat down to sort the stars by their spectra, and they needed yardsticks, stars that would hold still while everything else got measured against them. CE Cam was one. It's been a standard ever since. Every supergiant of its type you ever heard of, somebody decided what it was by holding it up next to that star." He tapped the screen. "CS is near enough its twin. Same mass, a hair smaller, neither one showing off. That's the point."

"Suppose your fancy computer takes a hit," he went on. "Catalog scrambled, clock drifting, the whole beautiful electronic brain convinced it's somewhere it isn't. What have you got? Your eyeballs, and two stars that have been saying the same thing for longer than there have been people. A navigator who knows the reference can check everything else. A navigator who doesn't is a passenger in a nicer uniform." Ruiz studied the pair a long time. Somewhere on old Earth, she recalled, a man had spent twenty hours photographing these two just to see them properly. She had thought that eccentric. She was beginning to understand it.

Brandt had retired by the time the Margaret Kelly lost her main computer in a magnetic storm three weeks out from port. Ruiz brought her home by hand, sighting on the Twins every watch. At the inquiry the board asked where she had picked up such an old-fashioned technique. "From a standard," she said. "You measure everything else against him."

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