On the surface of the Sun, spots appear and fade in a predictable cycle, like a great clock in the sky. In medieval Russia, China, and Korea, monks and court astronomers recorded the appearance of these dark shapes, interpreting them as omens of things to come. In Western Europe, by contrast, where a cosmology originating with Aristotle prevailed, the Sun was regarded as part of the unchanging celestial realm, and it took observations through telescopes...