The word zodiac is derived from the Greek ζωδιακός (zodiakos), which means "a circle of animals", or, as some believe, "little animals". It is the name given by the old pagan astronomers to a band of fixed stars about sixteen degrees wide, apparently encircling the earth. Robert Hewitt Brown, 32°, states that the Greek word zodiakos comes from zo-on, meaning "an animal". He adds: "This latter word is compounded directly from the primitive Egyptian radicals, zo, life, and on, a being".
The Greeks, and later other peoples influenced by their culture, divided the band of the zodiac into twelve sections, each being sixteen degrees in width and thirty degrees in length. These divisions were called the Houses of the Zodiac. The sun during its annual pilgrimage passed through each of these in turn, Imaginary creatures were traced in the Star groups bounded by these rectangles; and because most of them were animal--or part animal--in form, they later became known as the Constellations, or Signs, of the Zodiac.
Each year the sun passes entirely around the zodiac and returns to the point from which it started —the vernal equinox— and each year it falls just a little short of making the complete circle of the heavens in the allotted period of time. As a result, it crosses the equator just a little behind the spot in the zodiacal sign where it crossed the previous year. Each sign of the zodiac consists of thirty degrees, and as the sun loses about one degree every seventy two years, it regresses through one entire constellation (or sign) in approximately 2,160 years, and through the entire zodiac in about 25,920 years. (Authorities disagree concerning these figures.) This retrograde motion is called the precession of the equinoxes. This means that in the course of about 25,920 years, which constitute one Great Solar or Platonic Year, each one of the twelve constellations occupies a position at the vernal equinox for nearly 2,160 years, then gives place to the previous sign.
But the slow progressive disappearance of the Bull is most happily commemorated in the vanishing series of letters so emphatically expressive of the great astronomical fact. For ABRACADABRA is The Bull, the only Bull. The ancient sentence split into its component parts stands thus: Ab'r-achad-ab'ra, i. e., Ab'r, the Bull; achad, the only, &c. — Achad is one of the names of the Sun, given him in consequence of his Shining ALONE, — he is the ONLY Star to be seen when he is seen — the remaining ab'ra, makes the whole to be, The Bull, the only Bull; while the repetition of the name omitting a letter, till all is gone, is the most simple, yet the most satisfactory method that could have been devised to preserve the memory of the fact; and the name of Sorapis, or Serapis, given to the Bull at the above ceremony puts it beyond all doubt. This word (Abracadabra) disappears in eleven decreasing stages; as in the figure. And what is very remarkable, a body with three heads is folded up by a Serpent with eleven Coils, and placed by Sorapis: and the eleven Volves of the Serpent form a triangle similar to that formed by the ELEVEN diminishing lines of the abracadabra.
As the zodiacal band marks the pathway of the sun through the constellations, it results in the phenomena of the seasons. The ancient systems of measuring the year were based upon the equinoxes and the solstices. The year always began with the vernal equinox, celebrated March 21 with rejoicing to mark the moment when the sun crossed the equator northward up the zodiacal arc. The summer solstice was celebrated when the sun reached its most northerly position, and the day appointed was June 21. After that time the sun began to descend toward the equator, which it recrossed southbound at the autumnal equinox, September 21. The sun reached its most southerly position at the winter solstice, December 21.