Comets in kind are far from uncommon. As an approximate average, one appears every 18 months or so, and it is not unusual to see more than two in one year.

The record so far appears to have been in 2004, with a total of five comets visible without visual aids. But in 2006, 1970 and 1911 was not much delayed with a total of four each.

However, the majority of these pass unnoticed by the general public. Most of them simply look like mysterious stars with tails that are either weak or less than a threshold with the naked eye.

The "classic" comet - a starlike object with a long, flowing tail - is a scene that emits our sky once every 10 years on average. These "great comets" are certainly among the most beautiful things we see in the heavens, and no wonder they created such fear in earlier times.

Just what makes the comet "gorgeous" is not easy to define. It is not just a brightness and not just a matter of size.

Some comets can practice a surprisingly long tail however not considered large. Others can become very bright, but rarely seen by anyone other than a handful of ardent astronomers.

Much depends on their separation from the sun, the intensity of the tail, and so forth.