Modern scholars have long struggled to understand the sophisticated workings of Babylonian astronomy and, in particular, how the scribe derived from observation the numerical parameters of their planetary theory in this book, N. M. Swerdlow offers a solution to that problem. He examines here the collection and observation of ominous celestial phenomena and of how intervals of time, locations by zodiacal sign, and cycles in which the phenomena recur were used to develop a purely arithmetical planetary theory by which the same ominous phenomena that were regularly observed were reduced to computation, thereby surmounting the single greatest obstacle to observation: bad weather.