A highly informative account of those elusive visitors from space that have mystified man for many centuries. Past civilisations considered comets to be harbingers of disaster or omens of divine intent; military successes and failures were often attributed to the appearance of a comet over the battle field. And in 1456, Pope Calistus III was said to have excommunicated a comet (later charted by and named after Edmond Halley) as an agent of the devil! Patrick Moore sets out by explaining the basic structure of a comet and its relation to the rest of the solar system, describing the effects that the planets - especially Jupiter - can have on comets' orbits. The author indicates that anyone with keen eyesight can become a comet hunter, and may be able to contribute information about position, orbit, brightness and periodicity. The book also describes the famous comets of the past: Halley's comet, the first comet to be recognised as periodical; Biela's comet, which split in two and dissolved into a shower of shooting stars; and the recent crop of comets such as Bennett's, Arend-Roland, Ikeyi-Seki, West's, and the great comet disappointment of 1973-4 - Kohoutek. The book is illustrated with explanatory diagrams and photographs, and includes tables of the known periodic comets and a glossary of terms. It will be invaluable for both the amateur astronomer and the casual viewer of the night sky.