Do you know the current phase of the moon? Most of us don’t have any idea; nowadays we hardly need to know. But before there were streetlamps and electric lights everywhere, people watched the night sky diligently. So when a very bright comet appeared in 1607, people were frightened and fascinated.
German astronomer Johannes Kepler thought deeply about what he saw that year. He reasoned that the spectacular tail of what we now call Halley’s comet (named after English scientist Edmond Halley, who computed its orbit) was probably caused by the sun’s warmth somehow evaporating or liberating material from the comet’s surface. Kepler imagined exploring those star scapes: “Given ships or sails adapted to the breezes of heaven, there will be those who will not shrink from even that vast expanse,” he wrote.
Ships, after all, were common enough in the 16th and 17th centuries, and they were driven by the winds, which are themselves created in part by the sun’s warmth. Kepler lived during a moment in history when, thanks to Nicolaus Copernicus, we came to understand that we’re aboard a planet orbiting a star. Perhaps it was natural, then, for Kepler to envision humankind sailing the starry heavens.