Cosmos - Carl Sagan [44]
Comets have always evoked fear and awe and superstition. Their occasional apparitions disturbingly challenged the notion of an unalterable and divinely ordered Cosmos. It seemed inconceivable that a spectacular streak of milk-white flame, rising and setting with the stars night after night, was not there for a reason, did not hold some portent for human affairs. So the idea arose that comets were harbingers of disaster, auguries of divine wrath—that they foretold the deaths of princes, the fall of kingdoms. The Babylonians thought that comets were celestial beards. The Greeks thought of flowing hair, the Arabs of flaming swords. In Ptolemy’s time comets were elaborately classified as “beams,” “trumpets,” “jars” and so on, according to their shapes. Ptolemy thought that comets bring wars, hot weather and “disturbed conditions.” Some medieval depictions of comets resemble unidentified flying crucifixes. A Lutheran “Superintendent” or Bishop of Magdeburg named Andreas Celichius published in 1578 a “Theological Reminder of the New Comet,” which offered the inspired view that a comet is “the thick smoke of human sins, rising every day, every hour, every moment, full of stench and horror before the face of God, and becoming gradually so thick as to form a comet, with curled and plaited tresses, which at last is kindled by the hot and fiery anger of the Supreme Heavenly Judge.” But others countered that if comets were the smoke of sin, the skies would be continually ablaze with them.
The most ancient record of an apparition of Halley’s (or any other) Comet appears in the Chinese Book of Prince Huai Nan, attendant to the march of King Wu against Zhou of Yin. The year was 1057 B.C. The approach to Earth of Halley’s Comet in the year 66 is the probable explanation of the account by Josephus of a sword that hung over Jerusalem for a whole year. In 1066 the Normans witnessed another return of Halley’s Comet. Since it must, they thought, presage the fall of some kingdom, the comet encouraged, in some sense precipitated, the invasion of England by William the Conqueror. The comet was duly noted in a newspaper of the time, the Bayeux Tapestry. In 1301, Giotto, one of the founders of modern realistic painting, witnessed another apparition of Comet Halley and inserted it into a nativity scene. The Great Comet of 1466—yet another return of Halley’s Comet—panicked Christian Europe; the Christians feared that God, who sends comets, might be on the side of the Turks, who had just captured Constantinople.
The leading astronomers of the sixteenth and seventeenth centuries were fascinated by comets, and even Newton became a little giddy over them. Kepler described comets as darting though space “as the fishes in the sea,” but being dissipated by sunlight, as the cometary tail always points away from the sun. David Hume, in many cases an uncompromising rationalist, at least toyed with the notion that comets were the reproductive cells—the eggs or sperm—of planetary systems, that planets are produced by a kind of interstellar sex. As an undergraduate, before his invention of the reflecting telescope, Newton spent many consecutive sleepless nights searching the sky for comets with his naked eye, pursuing them with such fervor that he felt ill from exhaustion. Following Tycho and Kepler, Newton concluded that the comets seen from Earth do not move within our atmosphere, as Aristotle and others had thought, but rather are more distant than the Moon, although closer than Saturn. Comets shine, as the planets do, by reflected sunlight, “and they are much mistaken who remove them almost as far as the fixed stars; for if it were