Chalk up another neat and stylish text-with-pictures by the English astronomer Patrick Moore. This one focuses on comets--great ones and small, long-tailed or short, periodic visitors or one-time guests, still burning bright or fast fading away. Moore traces the history and early theories of comets' origins and their frequent associations with disaster, whether social or political (one celebrated appearance of Halley's Comet was in 1066). We've come a long way from believing that comets were some earthly miasma or the spin-off of some giant planet. But the origins of the flimsy, fragile objects remain mysterious. More is known about their composition. A nucleus at the core of the comet head appears to be a conglomerate of rocky particles and frozen gases; the tail may be made up of gases, dust particles, or both. When a comet nears the sun it loses part of its substance as the gases evaporate, some being blown back to form a luminous tail. The presence of solar wind and the pressure of the sun's rays are sufficient to keep the comet's tail always headed away from the sun. All this and lore about the peculiar breed of comet fanciers--patient and perceptive folk--as well as details of major sightings past and future, tables, glossary, and index make this a boon to the budding astronomer or the armchair observer.