This latest of Branley's trim, to-the-point introductions highlights how the Pioneer and Voyager probes have increased our knowledge of Saturn--and how much is still unknown. He reports on the planet's size and shape, rotation and revolution, temperature, density, mass, and gravity, always comparing these properties to those of earth to give the figures meaning. (""If Saturn were hollow more than 760 Earths could fit inside""; and, like most planets, ""Saturn is not round like a baseball. It is more the shape of a beach ball when you sit on it."") The rest of the book deals with the number, composition, and theories of origin of Saturn's rings (""Before Pioneer and Voyager scientists thought there were three or four or maybe six; now we know many more, perhaps thousands"") and some of its 22 or more satellites.