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 schedule. Its discovery was hailed as a triumph of scientific reasoning and Newtonian physics. “By its appearance at this time, the truth of the Newtonian Theory of the Solar System is demonstrated to the conviction of the whole world, and the credit of the astronomers is fully established and raised far above all the wit and sneers of ignorant men,” the British publication the Gentleman’s Magazine wrote. Shortly thereafter, the French astronomer Nicolas-Louis de Lacaille named the comet in Halley’s honor.
Scientists now believe that comet 1P/Halley, as it is formally known, has been zipping through the solar system for as many as 200,000 years. Edmond Halley only identified a handful of occurrences of his comet, but other scholars have plotted its earlier appearances and uncovered historical references dating back to the ancient world. In a 2010 paper in the Journal of Cosmology, researchers Daniel W. Graham and Eric Hintz suggested that one of the earliest known sightings of Halley’s comet may have occurred around 466 B.C. in the skies over Greece. Ancient accounts of the incident mostly center on a “wagon-sized” meteorite that landed in the Hellespont, but they note that the strike was accompanied by a “huge fiery body” that was visible in the sky for 75 days. According to Graham and Hintz, the timetable matches up almost perfectly with Halley’s comet’s projected appearance in the fifth century B.C.
While it’s possible that the comet the Greeks saw was Halley’s, more reliable accounts of its flybys didn’t appear for another few centuries. One of the most famous references is found in China in the Han Dynasty’s “Records of the Grand Historian,” which describes a “broom star” that appeared in the sky in 240 B.C. Other early sightings came from the Babylonians, who recorded the comet’s 164 B.C. and 87 B.C. transits on clay tablets; and from the Romans, who made reference to it in 12 B.C.
Halley’s comet inspired both fascination and horror in its early observers. The celestial visitor was often considered a bad omen, and it was linked to everything from the death of kings to natural disasters. The historian Flavius Josephus described the comet of 66 A.D. as a “star resembling a sword” and considered it a portent of the destruction of Jerusalem by the Romans. Several centuries later, the comet of 451 was thought to signal Attila the Hun’s defeat at the Battle of the Catalaunian Plains. In 837, meanwhile, the Holy Roman Emperor Louis the Pious feared the comet was a signal of his downfall and tried to ward off its influence with fasting, prayer and alms for the poor.
By far the most famous appearance of Halley’s comet occurred in 1066, when it coincided with the Norman Conquest. According to the Anglo-Saxon Chronicle, in the months before William the Conqueror set sail for England, “a portent such as men had never seen before was seen in the heavens.” Contemporary observers considered the “long-haired star” a bad omen for the English King Harold II, and the prophecy was later fulfilled when William defeated and killed him at the Battle of Hastings. Halley’s comet was later included in a section of the famed Bayeux Tapestry, which depicts King Harold and a crowd of fearful Englishmen watching it streak through the sky.
The strange effects of Halley’s comet only continued over the next several centuries. Its 1222 appearance is sometimes credited with inspiring Genghis Khan to dispatch his Mongols on an invasion of Europe, and its 1456 return famously overlapped with the Ottoman Empire’s invasion of the Balkans. The comet may have also crept into works of art. After viewing it in 1301, the Italian artist Giotto is said to have depicted Halley’s comet as the star of Bethlehem in his painting “Adoration of the Magi.”
People began watching the comet with a more scientific eye in the 16th and 17th centuries, but it was still causing anxiety as recently as 1910. As the comet neared the Earth that year, the New York Times wrote that a French astronomer named Camille Flammarion had warned that poisonous cyanogen gas in its tail might “impregnate the atmosphere and snuff out all life on the planet.” Other scientists dismissed the claim as nonsense, but the prediction still sparked a minor panic. Before the comet passed by without incident that spring, many people sealed up their homes to keep out the fumes, stocked up on gas masks, and went to churches to pray for salvation. The more gullible among them even bought “anti-comet pills” from street vendors.
Halley’s most recent return in 1984 marked the first time that scientists were able to study it with sophisticated technology. High-powered telescopes were trained on the comet from Earth, and five unmanned space probes dubbed the “Halley Armada” conducted flybys as it made its transit. One of them, the European Space Agency’s “Giotto,” even inched within 370 miles of the comet’s nucleus. The high-quality images returned by the probes were the first of their kind and provided fascinating insight into Halley, including proving once and for all that its core is a solid mass primarily composed of dust and ice. So far, no space agency has announced plans for another mission in the future, but there’s still plenty of time: the famed comet is not scheduled to make its next visit to the inner solar system until July 2061.