"Fever, sickness, plague, and death,
Hard times, need and hunger's scathe,
Great heat, drought, and barren Nature,
War, murder, riots, fire and slaughter,
Frost, cold, storms, and want of water."
Josephus tells us that the destruction of Jerusalem in 69 A.D. was caused by no less than the sword shaped comet which pierced the heavens above the city!
A story is sometimes told of the great consternation caused in Europe in 1456 at the appearance of Halley's comet. This great shaft of light moving across the sky so disturbed the equanimity of Pope Calixtus that he instituted a form of prayer ("Lord, deliver us from the devil, the Turk and the comet") as a protection against its baleful influence. But the comet remained, and, with his people mightily afraid, the pope himself was forced "to interfere, exorcise and expell" the malignant one from the skies.
Halley's comet has always been a most interesting comet. The last time that it appeared, in 1910, the earth rolled right through its beautiful, highly diffused tail, and although the experience was of interest to astronomers, it affected not a whit the affairs of the populace; indeed, but few people knew about it.
In 1680, Halley, an English astronomer and mathematician, while on a passage to France, was the first to observe this great comet, and later made observations with Cassini at Paris, where he observed its appearance with great care and painstakingly computed the elements of its orbit. From the nature of its orbit, he predicted that it would return at regular intervals of 75 years. He even traced this comet back on his historical table of comets, and found that the comets of 1607, 1531 and 1456 had the same orbit as the one which had appeared in 1680. Seventy-five years after, true to his prediction, the comet returned, thus proving that comets may travel in elongated orbits and appear periodically. Halley has the honor of being the first to predict the return of a comet.
It is now known that some comets require hundreds and even thousands of years to perform a revolution around the sun; Donati's comet, one of the most famous comets, which appeared in 1858 "like a plume of fire, shaped like a bird of paradise," travels on such a long circuit that it returns only every 2000 years. The brilliant comet of 1811, which remained visible for nearly ten months, has a period estimated as being around 3000 years. But the orbits of some comets are even longer than this, some traveling so far into space that they not only over-leap the boundary of Neptune but fly to a turning-post so distant that we may never see them return. More than 30 short period comets have been discovered and these have their orbits entirely within the solar system. Encke's comet, with a period of 3½ years, has the shortest period known.
Although it was discovered to the relief of mankind that comets have no influence upon the earth, it was also discovered that some of the planets with great mass and strong gravitational power, can exert considerable influence on a comet, in fact, enough influence to attract many of these celestial bodies out of their courses and force them to make their outer turn around a point near that planet's orbit. Jupiter has a larger family of comets than any other planet. If a planet once captures a comet it is his captive forever, unless the near approach of some planet of greater mass pulls the comet away and forces it to enclose its new master in the outer end of its orbit.
A large comet first appears among the stars as a dim spot of light. It may appear from any direction, for, although comets are considered members of the solar system, their orbits do not lie in the same plane as the planets. As it sweeps toward the sun with terrible velocity, which increases hourly, a long streamer of luminous gas gradually develops and floats backward from its head. A small comet often has no tail, but a large comet usually possesses a long and beautiful one, and has been known to possess two, and even half a dozen. This tail, or tails, are at their best when close to the sun, although at all times swung carefully away from the terrific flames of that luminary. Scientists almost hold their breath sometimes at the close call of comets, for the Great Comet of 1843 almost grazed the surface of the sun and many another has passed right through the outstretched banners of the corona. After darting swiftly around this brilliant center, the comet again heads into fathomless space, its long, bright tail gradually disappearing and its fierce speed relaxing as it escapes farther and farther from the sun's control.