The word "zodiac" means "circle of animals," and the name refers to the means taken by ancient astronomers to identify its various parts. Selecting stars that could be connected by lines to give a rude representation of some appropriate figure, they established twelve of these. The original signs, traced out this way in star patterns, are known as the "constellations" or collectively as the "natural zodiac," and they are seldom used in astrology. The reason is that the astronomical point which is taken as the zodiac’s beginning has a very slow clockwise movement in the skies. This is known as the "precession of the equinoxes," and it is sometimes used to define the great "ages" of human history. In the more than two thousand years since the zodiacal signs were established, the star-patterns which still name them are found about a whole sign out of position. This fact, not understood by opponents of astrology, is often cited as evidence of its supposed "unscientific basis."

The "animal" designations of the various signs were not only for the purpose of identifying the twelve sections of the heavens, but were also designed to dramatize the successive stages in human experience. The sun as a symbol of the will makes its annual "pilgrimage" through the zodiac and the order of events, or seasons of effort, are visualized as "ordeals" which in one way or another are typical in the lives of all men. This is the concept which took classical form in the twelve "labors of Hercules."

Since each person has his sun at birth in one out of these twelve divisions of the zodiac, the signs also sort people into twelve classes. Each class gives a special emphasis of some one part of the experience symbolized by the whole annual pilgrimage of the sun, or the will. The idea is that each man is found at some special point in this "pilgrimage" because it affords him the fullest chance to use his particular talents. The resulting concept of twelve basic types among human beings is represented in the twelve tribes of Israel and the twelve apostles.