An unusual hybrid, this is a Christmas/science book for juvenile readers. The author, who has written numerous books about astronomy, is director of the educational program at the Hayden Planetarium, and the text is derived from the Planetarium's annual Christmas program. In an easy to comprehend but quite readable, logical way, the Biblical text, historical sources, and astronomical calculations are discussed to derive the most plausible theory of when Jesus was born, and what the phenomenon was that the wise men called the ""star in the east."" No one should be offended by this treatment, which concedes, finally, that it may have been ""a miracle star."" It's an offbeat, intriguing subject for Christmas, and indirectly the book offers a good example of scientific method and of the interrelationship of science and history. Blair Lent's woodcuts, colored in blue, green, ochre, and gray, capture the simple, one-dimensional quality of medieval art, and are attractive enough to make this a possibility for gift-giving. The book will be particularly useful, however, for the special pre-holiday session in the class-room.