Comets herald the death of great men. Shakespeare says so in the play Julius Caesar, “When beggars die there are no comets seen. The heavens themselves blaze forth the death of princes.” The Bard was referring to history, or at least to myth.
According to classicist John T. Ramsey and physicist A. Lewis Licht, four months after Julius Caesar died a comet appeared, and shone so brightly it could be seen in daylight. Some Romans believed that this Caesaris Astrum bore Caesar’s deified soul away to heaven in 44 BC.
A skeptic or a scientist might wonder why the comet waited four months. A scientific explanation for such an appearance is that the comet reached a point in its orbit where the sun caused the particles streaming in its wake to ionize and glow, soon after the assassination of Julius Caesar.
Caesar’s Star was never seen again. It might be a comet with a very large orbit, which has not yet returned to a place near the sun. It might have broken up, lost mass and glow, or changed its orbit. A passing star might have kicked it into a new orbit. On the other hand, it might be entirely a myth, created out of moonshine and human credulity.
Comets can also foretell defeat in battle. In 1066, the appearance of Halley’s Comet signaled the doom of Saxon England. The comet looms over the battlefield in the Bayeux tapestry, the hanging that the women of the victorious side wove to celebrate the triumph of the Norman Conquerors.
Obviously, the Norman Conquest was not doom for the Normans. Halley’s Comet is a celestial object with a known orbit, which may be perturbed by the gravity of planets like Jupiter, but which is generally indifferent to earthly affairs.
A comet appeared again as the Black Death decimated the population of Europe in 1665. Actually, a comet appeared in 1664, then an eclipse, and then, in 1665, another comet and the plague. The Great Fire of London followed in 1666.
Comets are as rare as epic catastrophe, and were once as frightening to the educated as to the ignorant. Given enough comets and enough disasters, some will be coincident, that’s all.
In 1910, the earth passed through the tail of Halley’s comet, and many feared they would die because of cyanide gas streaming there. Sales of gas masks soared. No one died of the comet, and no comet accompanied the First World War or the calamitous Spanish Flu epidemic of 1918.
Some once believed that a comet’s tail might set the air ablaze if it came close enough. Untrue. In reality, comets are as cold as space itself. As Ian Ridpath explains in A Comet Called Halley, comet tails glow with the reflected light of the sun in their dust tails, and also with ionization similar to the phenomenon that sets neon lights gleaming. Some small fraction of the dark rubble of space is composed of former comets, with their bright tails entirely lost to the solar wind.