Looking up at a clear night sky gives the impression that the galaxy is dense with stars. It’s not. Although it seems like stars are arranged cheek by jowl on a sphere that surrounds us, because their distances from earth vary widely—a feature that’s mostly lost on our feeble, closely set eyes—stars are, in reality, quite far from one another. Were you to shrink the sun down to the size of a grain of sugar and place it at the Empire State Building, you’d have to drive most of the way to Greenwich, Connecticut, to encounter Proxima Centauri, our nearest stellar neighbor.
