Squint

In the CosmosForge observatory worked a small, twinkly-eyed creature named Squint, who wore two tiny sighting-tubes — one over each eye — and had a habit of closing first one eye, then the other, then grinning like she'd just won something.

Squint measured the one thing that seemed impossible to measure: how far away the stars are. "I'm Squint," she said, switching which eye was open. "I can't fly to a star and pace it out. Nobody can. But I have a trick. Hold up your thumb and look at it with one eye, then the other —" the students tried it — "see how your thumb jumps against the wall behind it? That jump is parallax. The near thing shifts against the far things when you look from two places. Stars do it too. And the size of the shift tells me exactly how far away they are."

A young stargazer wiggled his thumb, switching eyes, watching it leap back and forth. "But the stars don't move when I switch eyes." "Because your two eyes are too close together for something that far," Squint said. "So I use a much bigger pair of 'eyes.'" She spun a little model of Earth circling the Sun. "I look at a star now — and again half a year later, from the other side of our orbit, millions of miles away. That's like having two eyes set incredibly far apart. From those two faraway viewpoints, a nearby star shifts, just a little, against the distant ones behind it." The student watched the model swing from one side to the other. "And the bigger the shift...?" "The closer the star," Squint finished. "Tiny shift, faraway star. Big shift, nearby star. Two looks, and the distance falls right out."

The headmaster, Nova, asked Squint to teach a distance class. "The students think the stars are all stuck on one ceiling," Nova said. "Will you teach them that space has depth?" Squint loved the idea.

When she teaches, she gives one rule: "Never trust your one-eyed guess about distance — shift your viewpoint and watch. Look at a star from one side of our orbit, mark exactly where it sits among the far stars. Wait. Look again from the other side. Measure how far it jumped. The closest stars jump the most; the distant ones barely budge at all." A student tracked a near star across half a year, marked its little shift, and worked out its distance. "I measured how far away a star is," he whispered, "and I never left the ground." Squint beamed and switched eyes. "That's the first rung of the ladder. Once you can measure the near stars, you can use them to reach the farther ones, and those to reach farther still. Rung by rung, all the way out."

After class, Squint sat by the great window, idly closing one eye and then the other, watching the near lamp jump against the far wall, smiling to herself.