Book excerpt: The zodiac was first clearly defined by the Babylonians some 2500 years ago, but until recently the basis of this original definition remained unknown. This zodiac of the Babylonians, known as the sidereal zodiac because it is specified in direct relation to the stars (Latin sideris, 'starry'), was used for centuries throughout the ancient world, all the way to India, and must be distinguished from the tropical zodiac in widespread use by astrologers in the West today, which was introduced only in the middle of the second century A.D. by the Greek astronomer Claudius Ptolemy. Such was Ptolemy's influence, however, that the tropical zodiac gained prominence and, except for its survival (in a variant form) in India, knowledge of the sidereal zodiac was lost. In this thrilling study of the history of the zodiac, first submitted in 2004 as his Ph.D. thesis, Robert Powell rescues the the sidereal zodiac from the dusts of time, tracing it back to the Babylonians in the sixth/fifth centuries B.C. The implications of this discovery-among them the restitution of the sideral zodiac to its rightful place at the heart of astrology-are immense, they key point being that the signs of the sidereal zodiac, each thirty degrees long, coincide closely with the twelve astronomical constellations of the same name, whereas the signs of the tropical zodiac, since they are defined in relation to the vernal point, now have no direct relationship to the corresponding zodiacal constellations, owing to the precession of the equinoxes.This revolutionary history of the zodiac includes chapters on the Egyptian decans and the Hindu nakshatras, showing how these sidereal divisions, which originated in Egypt and India, are related to the original Babylonian zodiac. It also sheds light on the controversy surrounding the 'zodiac question' (tropical vs. sidereal), illuminating the history of the tropical zodiac-showing that originally it was not a zodiac at all, but a calendar for describing the course of the seasons! This book, the fruit of thirty years of research, is intended not only for scholars but for general readers as well, and offers the clearest and most comprehensive study of the history of the zodiac yet published.