The two philosophers labored to climb uphill under the pale glow of the crescent moon, their sandals crushing the parched soil underneath. As they approached the top of the mountain, the sky above exploded in a thousand flickering lights, the Milky Way stretching its ghostly arms across the darkness. Down below, one could see the burning torches of the amphitheater, the crown jewel of Miletus. Anaximander wiped his sweaty forehead on his sleeve and smiled at his younger student, Anaximenes. “Hard work pays off, right?” he said, between large breaths. Anaximenes stared at the heavens in awe. “Master, what do you think are these lights? Why do they stay up there, glowing steadily?” he asked. “Look carefully,” instructed Anaximander. “You can distinguish different kinds of light. Some flicker and others don’t. The ones that don’t flicker move slowly across the heavens. They are the planets. To see that they move, you need to watch them for a long time. Months. The ones that flicker don’t move.…