For much of history, comets were thought to be divine omens, atmospheric anomalies or celestial wanderers that flashed through the solar system before vanishing into interstellar space. All that started to change in 1705, when the English astronomer Edmond Halley published his “Synopsis Astronomia Cometicae.” By using Sir Isaac Newton’s gravitational theories to chart the paths of two dozen comets, Halley hit on a provocative new theory: three comets seen in 1531, 1607 and 1682 were actually the same object. Halley argued that the comet orbited the sun and whizzed by the Earth roughly once every 76 years, and he predicted that it would reappear sometime in late 1758 or early 1759. “If it should return, according to our predictions,” he vowed, “impartial posterity will not refuse to acknowledge that this was first discovered by an Englishman.”Halley was eventually proved correct on all counts. Although he died in 1742, his comet appeared in the sky on Christmas night of 1758, right on s...
