Generally consisting of a nucleus, head, and tail, comets are celestial bodies, similar in appearance to stars, whose origins and structures scientists are still in the process of determining. Because of their unusual shape and sudden appearances, comets were commonly viewed in ancient times as warnings or forerunners of great news. Aristotle was among those who believed comets were atmospheric phenomena because they were found outside the zodiac and they appeared to be different from planets. However, he also suggested that comets were weather signs, a statement that kept fear of comets alive for centuries.

When printing began, every comet appearance brought forth pamphlets with such titles as "News of the Terrible and Fearsome Comet." Halley's Comet (before it was so named) was especially seen in this light when it returned in 1456, just three years after the Turks had conquered Constantinople.

Nonetheless, there were those who looked scientifically...