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Comets (from Greek kométés, for long-haired) have been objects of awe, reverence and fear throughout history. The ancients, at least, had a legitimate excuse for their fantasies: no one knew where comets came from or where they went after they disappeared from sight. (Aristotle suggested that they were fiery "exhalations" in the atmosphere.) Whenever a comet appeared, it was taken as a sign from heaven of impending calamity: a flood, an outbreak of disease or even the fall of a king or empire. Plutarch wrote that a brilliant comet shone for seven nights in the sky over Rome after the assassination of Julius Caesar. In Shakespeare's dramatization of that event, Caesar's wife echoes the same theme: "When beggars die, there are no comets seen. The heavens themselves blaze forth the death of princes."
"Hairy Star." According to some biblical interpretations, a bright comet appeared over Judea around 7 B.C. shortly before the birth of Jesus. Oracles told King Herod that the "hairy star" was the harbinger of the birth of a boy who was destined to outshine the monarch himself. To thwart that threat to his supremacy, Herod went on a rampage of infanticide. In A.D. 451 a comet blazed overhead as Attila the Hun overran Gaul on a march that culminated in the invasion of Italy. A comet, depicted in the famous Bayeux tapestry, also appeared in the sky on the eve of the Battle of Hastings in 1066. William the Conqueror told his Norman soldiers that the comet was indeed a bad omen—for the English troops, who subsequently went down to defeat. In 1456, Pope Calixtus was said to have been so upset by the appearance of a comet after the Turkish conquest of Constantinople that he issued a bull of excommunication against the interloper—"to rid the earth and mankind of its calamities."
The comet of 1456 and many of the others that influenced ancient history were one and the same: the celestial visitor that became known as Halley's comet. A 17th century protégé of Isaac Newton, Edmund Halley was convinced that comets travel, like planets, in closed orbits around the sun. Using his mentor's formulas, he calculated the paths of comets dating back to 1337 and found that three—those of 1456, 1531 and 1607 —had roughly the same orbit as the comet of 1682 (which he had seen as a young man). Halley concluded that they were all the same object and boldly predicted that it would appear again in 76 years, the time it requires to make a single orbit around the sun. When Halley's comet reappeared on schedule in 1758, it offered convincing evidence that comets were really members of the solar system rather than messengers of God's wrath.