Toward the Modern Understanding of Comets

Abstract

Nevertheless even after their motion across the sky had been tamed by Newtonian gravity, the veil of mystery shrouding comets was merely loosened rather than completely torn away. The nature of these strange objects appeared to defy a simple explanation. They clearly were not solid bodies, like the planets, nor were they similar to the Sun and other stars. Even though the heads of some comets looked relatively dense, the fact that stars were most often visible, typically with little or no dimming, implied that they must actually be composed of very rarefied material. This applied even more to the tails that accompanied many comets, especially the brighter ones. These had no known counterpart among the features of other astronomical objects. Moreover, they did not necessarily stream out behind the comet’s heads, as one might imagine of a moving object. Instead, they appeared to be directed more or less away from the direction of the Sun, as noted by Chinese astronomers over 1000 years ago and again by Peter Apian in 1532.