The Horizons Are Receding

Not quite ten years had passed since Bruno’s tragic death when an event took place that would completely vindicate him and his master, Copernicus. On January 7, 1610, Galileo Galilei (1564–1642), by then already a renowned scientist, aimed his new telescope at the planet Jupiter. To his amazement, he found the planet surrounded by four small objects, which he correctly identified as satellites circling their parent body. He named them the Medicean Stars, in honor of the Medici family in whose service Galileo hoped to be employed. Here, then, was an entire solar system in miniature—a retinue of small bodies circling a large one—and it gave strong, though indirect, support to the theory of a heliocentric system (which even at that time was far from being universally accepted). Even stronger evidence came when Galileo discovered that Venus, a planet closer to the sun than the earth, exhibits phases like the moon—a convincing proof that it must be circling the sun and not the earth.1 He then directed his telescope (he called it a “spyglass”) at the moon and saw sights never seen before by the human eye—a heavenly body crisscrossed by valleys and mountains, by flat plains, and by “seas”—in short, an imperfect world not unlike our own and a far cry from the perfect crystal spheres of the Greeks.