The real ""curse of Halley's comet"" may be the flood of slick popularizations that are heralding its 1985-86 return. Whipple's book, however, is in a class by itself: a highly informative, well-written account of comets by the man who, during the 1950's, revolutionized our understanding of their often erratic behavior. Whipple, recently retired as head of the joint Harvard/Smithsonian Observatory, focuses on comets in general rather than on Halley's alone. In fact, he at once admits that next year's ""apparition"" (the astronomer's term) is, like 1974's Kohoutek, likely to disappoint most people. After a brief survey of Halley's early appearances and a chapter on its latest apparition in 1910 (when Mark Twain, as he had predicted, ""went out"" with the same comet that had appeared in 1835, the year of his birth), Whipple examines the general evolution of cometary science. Acknowledging that comets have always inspired fear, he speculates that this is because of their unpredictable, even delinquent, behavior. Their orbits--even in modern times--have proved much more difficult to plot than those of the planets. Indeed, the law governing gravitation laid down in Newton's Principia (whose publication, incidentally, was paid for by Newton's friend Sir Edmund Halley) is blithely ignored by comets. It remained for Whipple himself during the 1950's to correlate Einstein, Planck, and recent advances in spectroscopy with Newton, in order to postulate his now generally accepted ""Dirty Snowball"" theory of comet composition. Having noticed that some comets split into two or even vanish as they approach the sun, Whipple's stroke of genius was to suggest that perhaps they are melting! There is more to comets than that, of course; and several chapters here on the mathematics of orbit prediction are likely to be hard going for the amateur. On the whole, however, Whipple is an easy guide through this tortuous subject--endearingly modest in his account of his own contributions, and especially readable on the foibles of his star-gazing predecessors, whether he is discrediting canards (Halley did not discover a comet on his honeymoon) or mildly affirming his facts (Halley did once tail to receive a teaching post at Oxford on the grounds that he ""ate, drank, and swore like a sea captain"").