The Director of the Armagh Planetarium in Ireland clues the amateur astronomer in on some 400 words and phrases from ""aberration of starlight"" to ""zodiacal light."" Such basics as atom, photon, star, comet, horizon, are defined along with flocculi, flying saucers and Fraunhofer lines, Widmanstatten patterns and the Wilson effect. Illus. Direct, definite, useful. A title in the Amateur Astronomer's Library.