These days, it seems that every time we turn around, there's an thrilling new cometary event for us to train our telescopes on. It's almost as if the coming retinue of bright comets is seeking to outdo Shoemaker-Levy's spectacular impact of last July. Though we're understandably excited by this show, our ancestors would have been horrified. Indeed, this flurry of cometary activity in the last years of the old millenium might still convince the more superstitious that we're in for, as the rustics put it, "a whole mess o' trouble."
Despite recent advances in our understanding of these celestial wanderers, comets have had a difficult time shaking their reputation as harbingers of famine, war, pestilence, and other malevolent horsemen. Historically they have been almost universally regarded as ill omens. In fact, more societies in the history of the world have sanctioned incest than believed comets were lucky . The only exception I can think of are the !Kung people of Namibia, latter-day hunter-gatherers who believe that a comet in the sky heralds good fortune.
Other cultures have not been so optimistic. The Chinese, known for their meticulous observations, have left such fabulous relics as the Mawangdui silk, a textbook of 29 different cometary forms and the various disasters associated with them. Although complied sometime around 300 B.C., the knowledge it encompasses is believed to date far back as 1500 B.C. Noted astronomer Li Ch'un Feng has this to say on the subject of "broom stars":
Comets are vile stars. Every time they appear in the south, something happens to wipe out the old and establish the new.
Also, when comets appear, whales die.
...When a comet appears in the constellation Hydra, there is war
and some conspire to overthrow the emperor. Fish and salt are expensive. The emperor dies. Rice also becomes expensive. There
is no emperor in the country. The people hate life and don't even
want to speak of it.
Many historians believe that the Aztec ruler Montezuma II's sighting of a comet in 1519 caused him to believe his reign was at an end and to surrender to Cortés without much of a struggle, thus allowing a party of 400 Europeans to overwhelm a vast civilization of several million. Similarly, the visit of Halley's comet in the year 66 A.D. is seen as foretelling the destruction of Jerusalem.
The first tentative steps in understanding comets were made by the Greeks. They also linked comets with disaster (dis-astra or "against the stars"). Democritus thought that comets were produced when one "star" passed near to another. Given our present knowledge of the Oort cloud and the subtle gravitational tugs that can precipitate a cometary event, he seems to have been on the right track. More so, anyway, than Aristotle, who postulated that since the heavens were pristine and unchanging, comets were merely atmospheric phenomena. This view was not challenged until 1577, when Tycho Brahe collaborated with other astronomers across Europe. Separately, they observed the great comet of that year and upon comparing their measurements, found none of the parallax that would surely be evident had comets in fact been as close as Aristotle predicted.
Why is it that so many diverse cultures have agreed on the unwholesome nature of comets? It is difficult to say. However, Carl Sagan correctly notes that since human history has not been unduly happy, "... any comet at any time viewed from anywhere on Earth is assured of some tragedy for which it can be held accountable."
Now that many of us see these phenomena in a more scientific light, its tempting to laugh at these ancient beliefs. But we must remember that not all aspects of cometary superstition were bad. Fear of these "hairy stars" spurred kings and emperors to commission grand observatories. There wasn't a decent court without a well-heeled astronomer to warn it of impending doom. Then again, the stress of imminent execution for failing to predict a cometary appearance might well have made the job less than fun.