With the field of vision limited by the horizon, and further obscured by the atmosphere, it’s not possible to see more than twenty miles from any given coastline. From the peaks of the world’s higher mountains, this range will extend by a few hundred miles, given a clear, bright day. But it is something else entirely to look straight up on a cloudless night, where , from trillions of miles away, we can see objects that existed billions of years ago. The view encompasses time and space in measures unlike any we’ll traverse in our own lives. And though the stars appear to revolve around us, their relationships to one another seem utterly fixed—not just over the course of a lifetime, but across thousands of generations.
For navigators finding their way between fixed points on the Earth’s surface, the stars have long provided a reliable indicator of direction. For cartographers attempting to illustrate what lay beyond any given horizon, the same stars provided standard points of reference for their own craft. The limits of this craft—and by extension, of what navigators could hope to reach safely—had been defined in large part by shared knowledge of patterns visible in the deepest regions of space. Celestial maps, like those shown here, both documented this common frame of reference, facilitating memorization by students, seafarers, and astronomers alike.