ABSTRACT
Comets are the most erratic members of the Solar System. In 1578 the Lutheran bishop Andreas Calichus went further, and described comets as being ‘the thick smoke of human sins, rising every day, every moment, full of stench and horror before the fact of God’. Comets were viewed with alarm partly for astrological reasons and partly because it was thought that a direct collision between the Earth and a comet might mean the end of the world. In 1948 the Cambridge astronomer R. A. Lyttleton popularized the ‘flying sandbank’ theory of comets. A comet is made up essentially of three parts; a nucleus, a head or coma, and a tail or tails. Faint short-period comets are common, and more are discovered every year. The comet with the shortest known period is J. F. Encke’s, named in honour of the mathematician who first computed its orbit. By June 1994 the comet had reached the halfway point between perihelion and aphelion.
