Comets are the most erratic members of the Solar System. They may sometimes look spectacular, but they are not nearly so important as they then seem, and by planetary standards their masses are very low indeed. In most cases, though not all, their orbits round the Sun are highly eccentric. A comet has been aptly described as a dirty ice-ball.

COMET PANICS

In earlier times comets were not classed as being celestial bodies, and were put down as atmospheric phenomena, although it is true that around 500 BC the Greek philosopher Anaxagoras regarded them as being due to clusters of faint stars. They were always regarded as unlucky. Recall the lines in Shakespeare's Julius Cæsar:

When beggars die, there are no comets seen:

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 face of God’. However, his Hungarian contemporary, Andreas Dudith, sagely pointed out that in this case the sky would never be comet-free! The first proof that comets were extraterrestrial came from the Danish astronomer Tycho Brahe, who found that the comet of 1577 showed no diurnal parallax, and must therefore be at least six times as far away as the Moon (actually, of course, it was much more remote than that).