A Brief (if not grossly oversimplified)
History of the Tropical Zodiac
Ancient Calendar-Computers “Clock” Movements of the Sun, Moon & Stars
Empirical evidence suggests that the various zodiacs in early recorded history were arbitrary arrangements of the Heavens designed to act mainly as calendars and navigational aids. [See Cyril Fagan quote in endnote below.] Stonehenge, for example, is popularly thought to be a standing astronomical computer-calendar that operates something along the lines of a sun dial.
There were plenty of other motivations in ancient times for keeping systemic track of the movements of Sun, Moon and Stars. After hundreds of years of studying Egyptian, Aztec, Mayan and Incan ruins in relation to the Sun and the Moon, the most staggering breakthroughs were made after it was ascertained the Great Pyramids were built to align Egypt with certain constellations in the Northern skies — most notably constellation Orion and the three stars of Orion’s Belt. See Precise Astronomical Dating of the Great Pyramid and THE ANCHOR OF THE WORLD: Did the Pyramid Builders of the Old Kingdom use the Pole of the Ecliptic? - Robert G. Bauval.
Ancient Astronomy-Astrology — a Single Science
Astronomy and Astrology were at one time a single science that most authorities agree was brought to Egypt by Thoth the Atlantean. The earliest known Egyptian zodiac featured 8 divisions representing the upper echelon of the Egyptian pantheon. Subsequent cultures added to and subtracted designs from the ecliptic plane (zodiac belt) until finally, by some accounts but not without conflicting evidence to the contrary, the Romans put the finishing touches to the Western Zodiac by snipping the claws off the Scorpion to create a 12th constellation which they called Libra. To this day the pans of the Libra scales are often referred to by their ancient names Zubeneschamali and Zubenelgenubi meaning Northern and Southern Claw respectively. (See Anne Wright’s Constellations of Words web site.)
Meanwhile in other parts of the world, calendaring systems and architectural wonders were being devised, designed and built implementing alignments and angular units of measurement as suggested by the Sun, Moon, Planets & Stars but from different perspectives due to differing cultural ideologies. Some cultures built their calendar systems based on the cycles of the Moon rather than those of the Sun. But an astounding number of these sites world-wide no matter what their cultural / ideological orientation were connected by a common grid principle (See Graham Hancock’s Forum: Jim Alison – Sites Around the World) implying there was once a vital underlying connectivity on this planet. With the recent rediscovery of the Sacred Geometry relationships of these sites to one another the empirical evidence undeniably demonstrates that there was in fact a time in history when the connection between Earth and Sky was scientifically used for some well-considered purpose and that there was intelligent, harmonious, cross-cultural communication between and among the dwellers on the continents/plates.
The agrarian celestial calendar develops – oracular vocabulary builds
As Human society proliferated and became increasingly more complex the Western World had entered into a phase of developing its new mystic and occult personae. Works published by many of the Philosophers of the time in contemplation of the metaphysics, theology, theosophy, and religion, questioning the nature and constitution of the cosmos and the human soul were plentiful. At some point in and amongst all of this metaphysical growth Western Astronomy-Astrology evolved as part of that movement, and the “Houses” and “Signs” of the zodiac were expanded to encompass more than simple agrarian concepts as the whole system had outgrown the original definition of astrology as a calendar-navigational-alignment device and became a spiritual guidance tool for tracking celestial alignments believed to be signs foretelling the cycles and windows of fortune and fate.
Up to this point Astronomy-Astrology was one-and-the-same “art/science”. But the soul of this marriage was soon to fall upon hard times.
Astronomy and Astrology Part Ways
Particularly important in the development of Western horoscopic astrology was the astrologer and astronomer Ptolemy, whose work Tetrabiblos laid the basis of the Western astrological tradition. Under the Greeks, and Ptolemy in particular, the planets, Houses, and signs of the zodiac were rationalized and their function set down in a way that has changed little to the present day. Ptolemy lived in the 2nd century AD, three centuries after the discovery of the precession of the equinoxes by Hipparchus around 130 BC, but he ignored the problem, by dropping the concept of a fixed celestial sphere and adopting what is referred to as a tropical coordinate system instead.
The Roman Inquisition of 1615 forced Astrologers and Astronomers to part ways. Scientific measurements had proven that the Earth was not the center of the Universe and that the Earth traveled around the Sun, not vice versa. This was proclaimed a great heresy by the Church Fathers and war was waged against the astronomy-astrology scientists who were prosecuted and persecuted left and right.
Today the Tropical Zodiac created by the Father/Mother of the science of astronomy is so far removed from physical Third Dimensional reality on account of the expansion of the Universe and constant movement of the fixed stars and equinoctial points, astrologers are stereotyped as quacks by tunnel-vision astronomers who think they know something about reality and reason but refuse to step outside of the box to see what is on the other side of the question. Conversely, astrologers are dragging their feet, reluctant and resistant to restore celestial sphere integrity to their system of … whatever it has become by now. It is certainly not based on the real sky anymore. If it were, I would be a professional astrologer for 15 already by now instead of going out on a limb with Astronomology.
So to sum it all up, between the two estranged camps, astrology and astronomy, we both have a lot of growing up and growing back together to do – all for a very good cause. Let us cheer each other on in our efforts and move forward learning from each other to improve the fullness of life in all of its beauties in the best interests of harmony on the planet and service to humanity.
 “ The Dodekotopos, which is the vogue today throughout the whole astrological world, appears to have been culled from the hermetic writings of Hermes Trimegistos, literally the “thrice greatest Thoth”, and is supposed to be of Egyptian origin. But Thoth is the Egyptian god of the Moon while Hermes is the Greek for Mercury; [Ed. N. : This remark is significant, but the conclusion ? :] so the Dodekotopos is, in fact, a Hellenic rendition of an Egyptian original, which rendition violates at every point the archetypical fitness of things. What appears to be the original, and hence authentic, scheme of houses is described in the Greek Michigan Papyrus No. 149, probably written by the pseudo-Manetho, born in A.D. 80, of which a translation by the Greek scholar, Rupert Gleadow, appeared in the September and October 1950 issues of American Astrology magazine. It also is described in the Astronomicon of Manilius who flourished in Rome during the reigns of the Emperors Augustus and Tiberius. (Manilii Astronomicon, ed. A.E. Housman, London, Grant, 1903-1930). Known as the Oktotopos – okto meaning eight and topos, places – it comprises only eight houses and these run clockwise, no attempt being made to make them tally with the zodiacal signs.
In the original scheme of things, as conceived by the early Egyptians, these so-called houses or places were not measures of space at all but measures of time; a fact which modern astrological mathematicians have utterly failed to grasp. So, instead of calling them houses or spaces, for want of a better name we shall designate them “watches”. The immortal Imhotep, of Sothic fame, is credited with having devised the Oktotopos. [Ed. N. : I remain very skeptic as for this origin. No reference is advanced.] Naturally the arms of the mundane crucifix, the framework of the chart, which defines the Ascendant, the Midheaven, the Descendant and the Anti-Midheaven (often erroneously called the Nadir) is  treated, and trigonometrically computed, as being spacial. The division of the mundane sphere into succedent and cadent lunes are also spacial. But in the matter of dominion, the Egyptians treated these watches as measures of time, just conventional time as ordinary people understand it.”
Cyril Fagan: The Oktotopos (with comments by Patrice Guinard), (version 1.1 : 01.2000)
E-Bibliography – corroborating sources
- In seeking to answer the question “why is the most popular astrological zodiac the most inaccurate?” I have adopted the theory espoused by Nick Kollerstom, author of INTERFACE: Astronomical Essays for Astrologers and Venus: The Rose & the Heart.
- See also School of Ageless Wisdom Basic Astronomy and Astrology