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Part One


This excerpt was first published in 2007 by The Mountain Astrologer Magazine

This is the first in a three part series on western sidereal astrology, its antecedents in the ancient Near East, and its renewal by Cyril Fagan, one of the greatest astrologers of the 20th century.  This series, which originally ran in the student section of The Mountain Astrologer, will also cover the introduction of tropical zodiac reckoning, the phenomenon of precession, the astrological ages, and a quick review of the works of Hipparchos of Rhodes and Claudius Ptolemy.

People new to astrology are often confounded by the two main schools of thought within it: tropical and sidereal.  Tropical astrology reckons positions of bodies from the Northern Hemisphere vernal equinox.  In this system, the zodiac is defined by the seasons and is disconnected from the stars as a frame of reference. It gained currency late in the first millennium B.C. in the Greek world and is practiced today primarily in the West.

Sidereal astrology reckons positions of bodies from the fixed stars.  In this system the zodiac is defined by the stars themselves and is disconnected from the seasons as a frame of reference.  The earliest form of sidereal astrology gained currency in the Near and Middle East in the second millennium B.C.  Sidereal astrology is practiced today primarily in India and among some Westerners, mostly British and American.  

There are two schools of sidereal astrology: eastern, also known as Indian, Vedic or Hindu astrology, and Babylonian, also known as western sidereal astrology.  Babylonian astrology is a familiar quantity in academia because it is very well documented.  Western sidereal astrology is built around the re-discovery in the nineteenth century of the sidereal zodiac employed in Assyria and Babylonia (modern Iraq) that spread throughout the Near and Middle East and the Mediterranean world. 

Eastern and western methodologies are similar in some respects, but the differences are great enough that the two schools can only be considered cousins, rather than brothers, joined mainly by their use of the sidereal zodiac.  Western sidereal methodology is closer to tropical astrology with the sidereal zodiac substituted for the tropical. 

In the ancient world, astrology and astronomy were, in effect, twin disciplines.  Every astronomical fact had an astrological corollary, a tenet astrologers still embrace. Early astrology was crude compared to its modern rendering, but it bloomed into a form roughly familiar to modern astrologers in the first millennium B.C.

The earliest Babylonian astronomical document to which a date can be affixed is from 1702 B.C and the last datable Babylonian astronomical document found to date is from A.D. 75. Babylonian materials are plentiful and well-edited from approximately1600 B.C. through to the height of the Roman Imperial Era in the first century of the Christian Era.  The earliest astronomical computations in the Middle East were concerned with the varying length of day and night, the rising and setting of the Moon and the appearance and disappearance of Venus.  The equinox was noted because of its integral role in the determination of the longest and shortest days. 

The most important texts for ancient astrology come from the city-states of Nineveh, Babylon and Uruk in ancient Mesopotamia, and the most important of those texts is the seventy tablet series known by its incipit: the Enuma Anu Enlil (“When [the gods] Anu and Enlil…”).  It is the richest source of second millennium B.C. astrological and astronomical information in the world. The Enuma Anu Enlil series deals with solar, lunar, planetary, stellar, zodiacal and meteorological lore and some omens.  Its astrology is called judicial because it deals with events and conditions that affect king and country; primary among those are issues that relate to war and peace, quality of the harvest and weather.  This was all derived from the positions of the Sun, Moon, planets and stars and sometimes the rising point of the ecliptic.  Modern astrologers do the same things, now mostly for individuals, but judicial or political astrology is still very much in vogue. 

A two tablet series titled Mul Apin (which means “plowstar”), that is part of the Enuma Anu Enlil series, deals extensively with astronomical lore including the simultaneous risings and settings of constellations, the time interval between the rising of paired constellations and the calendar dates that correspond to the risings and culminations of important stars in the Babylonian pantheon.  Mul Apin is a compilation that took centuries to complete.  Its completion date is firmly fixed at 687 B.C., and while some scholars place its genesis in the third millennium B.C., the latest work on this series strongly suggests that it dates from 1000 B.C. (1)

The zodiac took many centuries to sort out.  The twelve equal division scheme of thirty degrees each is not attested with certainty until 500 B.C., although there is compelling circumstantial evidence, that it is several centuries older than that.  Before they produced the modern twelve-fold division of the zodiac the Babylonians used an eighteen unequal division scheme that included the twelve constellations used today but with Pisces in two pieces (the eastern fish and the western fish) plus another constellation within Pisces called “the swallow” and with the addition of the Pleiades, Auriga, Orion and Perseus.  

The high water mark for Babylonian mathematical astronomy that transferred directly into an astrological context, covers the second half of the first millennium B.C.  The discoveries in the second millennium B.C. that most planetary and astronomical movements are periodic was an enormous stimulus to regular observation, record-keeping and mathematical treatment of those observations.

After the final determination of the reality of the zodiac, the main tool that allowed the Babylonians to graduate from omens to a broader, more extensive astrology, was a technique called period relations.  Period relations are a combination of sidereal periods and synodic periods.  A synodic period is the time elapsed between successive conjunctions of a planet with the Sun as seen from the Earth.  The synodic period for Jupiter, for example, is 398.88 days.  A planet’s sidereal period is the time it requires to orbit the Sun as seen from the Earth.  The sidereal period for Jupiter is 11.86223 years, but Jupiter’s period relation, discovered by the Babylonians, is thirty-six revolutions of that planet which is 427 years or 391 synodic periods.  That means Jupiter returns to the same positions in the zodiac very closely every 427 years with respect to its synodic phenomena, both in terms of order of occurrence and interval in time. A planet’s synodic phenomena are its first appearance (visibility), first stationary point, opposition (to the Sun), second stationary point and last appearance (visibility).  For example, in the current year Jupiter has had two stations; in terms of sidereal reckoning, it turned stationary retrograde on April 6, 2007 (N.S., i.e. New Style or Gregorian calendar reckoning) at 24° 56' and stationary direct on August 7, 2007 (N.S.) at 15° 05'.  Four hundred twenty-seven years ago Jupiter turned stationary retrograde on March 22, 1580 (O.S., i.e. Old Style or Julian calendar reckoning) at 25° 42' and stationary direct at 15° 51' on July 23, 1580 (O.S.). (2)  The agreement between 1580 and 2007 is close enough to allow someone with long term observations of the previous 427 years to predict Jupiter’s behavior quite accurately during its period relation that began in 2007 by comparing it to 1580.  The period relation of Venus is 1151 years; Mars is 284 years; Saturn is 265 years; Mercury is 46 years. The understanding of period relations was immensely valuable information much used by later astronomer/astrologers including the Greeks, the Indians and the Arabs.

Period relations are the main component of the first ephemerides, one of the greatest achievements of the Babylonians.  There is a difference, however, of more than five degrees between tropical and sidereal reckoning during Jupiter’s period relation that is at the root of how precession was discovered.  Actually, it is precisely this divide between tropical and sidereal reckoning that is only obvious over a period of centuries that gave rise to tropical reckoning itself.  Babylonian material is sidereal, but the Babylonians had no knowledge of precession—the element that separates tropical from sidereal reckoning.  Their use of the equinox was mainly to keep their calendar from drifting out of relationship with the solar year.  Their priority with respect to the zodiac is their supreme achievement; ephemerides rank next in importance.

Tropical and sidereal reckoning diverge with the career of the Greek astronomer Hipparchos of Rhodes. His dates are unknown but his career spanned the period 146-127 B.C.   Hipparchos made observations of stars that he compared against the first star catalogue compiled by a Greek, the astronomer Timocharis, one and a half centuries before Hipparchos’s time.

Hipparchos found that (the modern equivalent of) declinations (3) of some stars had increased in 150 years, some had decreased, some had stayed the same but that distances and positions of the stars with respect to each other had not changed, nor had their celestial latitudes. (4) Hipparchos’s observations were correct and the conclusions he drew from them completely logical based upon his underlying assumptions that the Earth was motionless and the center of the solar system.  He concluded that Spica (the brightest star in Virgo) had been eight degrees to the west of the autumnal equinox in Timocharis’s time, and from his own observations that Spica was six degrees to the west of the autumnal point in his own time. (5)  It is from this conclusion in combination with the declination comparisons to Timocharis’s star catalogue that Hipparchos deduced that there was definitely a slow motion between the stars and the equinoxes, heretofore unknown.  Hipparchos’s lasting fame rests more on this discovery called now “the precession of the equinoxes” than for any other part of his work.

The consequence of his discovery produced the modern tropical zodiac almost beyond question.  If one believes that the Earth doesn’t move and one observes motion between the equinoxes and the stars, then one is forced to conclude that the stars must be moving with respect to the Earth.  What is actually happening, now as then, is that the Earth moves with respect to an essentially fixed sky, but the Earth’s motion was not obvious by any experiment devised in Hipparchos’s time.  The stars do have motion with respect to the Earth but their motions are so infinitesimally small that in most cases it takes tens of thousands of years for an observer to see any change in their distances from each other.  Except for some relatively fast nearby stars (yet even these are still exceedingly slow except compared to a stellar average), it takes hundreds of thousands of years for stars to move as much as one degree with respect to the Earth.  So while the so-called fixed stars are not absolutely fixed, as a practical matter they are very much fixed to the naked eye.  The night sky looks now to the naked eye just as it did at the dawn of recorded history in Egypt circa 3000 B.C.

The premise behind Hipparchos’s logic is that the initial starting point of the zodiac has to be tied to something that won’t change.  Otherwise one has no absolute standard against which to measure bodies.  Yet if it is assumed that the Earth is fixed and the sky is moving, the signs reckoned from the vernal equinox—which moves one degree westward against the stars in 72 years—quickly get out of synchronization with the sidereal signs reckoned from the stars.  Sidereal reckoning is not subject to precession because its frame of reference is fixed to a star and an epoch that obviates the exceedingly slow motion of the stars themselves.  The zero degree of Aries, as defined by western sidereal reckoning, is the point forty-five degrees west of Aldebaran, the brightest star in the middle of the constellation Taurus at the epoch A.D. 1950.0. Thus, sidereal reckoning is “fixed” and tropical reckoning is called, "the moving zodiac."

The case has been made (6) by G.J. Toomer, whose translation of Ptolemy’s Almagest is unquestionably the best one, that Hipparchos concluded, at least at one point in his reasoning, that the equinox had moved (which is actually what had happened) and thus that it cannot be regarded as a fixed point on the ecliptic into perpetuity.  However this position (that the equinox had moved) was the end result of a long process that was intimately bound up in Hipparchos’s determination of the difference between the sidereal year and the tropical year.  Therefore it is not completely clear from the modest remnants of his work that he was confident of which frame of reference—the stars or the equinoctial points—was moving in relation to the other until, Professor Toomer thinks, the very end of Hipparchos’s career.  Another modern authority (7) with impressive astronomical and academic credentials also maintained that Hipparchos did adopt the hypothesis that the equinox had to be moving.  The rationale behind that assertion, explained by Professor W.M. Smart is that it is unreasonable to assume that every star Hipparchos examined from one era to the next had exactly the same proper motion, which is a requirement if the star field were moving against a fixed equinox.

Precession is well illustrated by observing the wobble inside the spin of a child’s spinning top.  It looks like the slow gyration of the rotation axis of a spinning body.  The Earth does the same thing due principally to its shape and the fact that its polar axis is not aligned with the pole of the plane of the ecliptic.  The angle between the ecliptic plane and the plane of the celestial equator is called the obliquity of the ecliptic.  It is currently 23 ½°.

The Earth, like any semi-rigid body that rotates even as fast as a merry-go-round, accumulates material around its equator.  The Earth moves at the rate of 1000 miles per hour at the equator, which is more than sufficient to deform a non-rigid sphere.  Accordingly, the Earth’s polar diameter is twenty-seven miles less than its equatorial diameter, which makes it an oblate spheroid due to its bulging equator.

The gravitational relationships between the Sun, the Earth and the Moon are experienced on the Earth side of the equation almost exclusively at the equatorial bulge.  The effect is to pull the Earth upright so as to bring the Earth’s polar axis into alignment with the ecliptic pole; however, a torque—in this case, gravitational attraction—applied to a rotating body will cause the body to respond at a right angle to the [vector of the] applied torque.  That means the Earth, because it is massive and spinning, is able to resist the gravitational forces of the Sun and the Moon that would otherwise change its orientation in space instantly; but the Earth is nonetheless affected by the gravitational attraction of the Sun and Moon tugging at its equatorial bulge and responds at a right angle to the force applied on it: its spin axis slowly wobbles.  This motion is too slow to be seen in a lifetime without instruments.  Due to the immense masses, forces and distances in this three-way relationship between the Sun, the Moon and the Earth, it takes approximately 25,800 years to complete a single wobble cycle.  Thus about every 2,100 years the Earth precesses through thirty degrees.  Those are the astrological ages.  The meaning of the term, “Age of Pisces”— in which we are now—is that if one looks due East on the morning of the Northern Hemisphere vernal equinox, one will see the Sun rise with the stars in the constellation Pisces because precession has carried the equinox away from Aries since Hipparchos’s time.

The next great figure in astrology and astronomy is Claudius Ptolemy who is separated from Hipparchos by three hundred years.  Ptolemy’s dates are also unknown although the best educated guesses place him between A.D. 100 and 175.  He wrote in Greek but lived in Alexandria, Egypt, the intellectual center of Late Antiquity in the West.  He was a polymath whose known fourteen works included not just astrology and astronomy but mathematics, optics and cartography.  Ptolemy thoroughly embraced the tropical zodiac and, like Hipparchos, was convinced of the immobility of the earth and that the solar system was geocentric (i.e., that the Sun orbits the Earth).  His career spanned the period when tropical and sidereal reckoning were almost identical at the very end of the age of Aries.  In other words what Ptolemy wrote about corresponded to what an observer saw; there was agreement between observation and theory, but only during that era. 

Among Ptolemy’s works, the two that profoundly influenced astrology in the West for 1500 years were the Syntaxis, a treatise on mathematical astronomy, and the Tetrabiblos, a treatise on astrology.  The Syntaxis is better known as the Almagest, which is the Arabic rendering from the Greek superlative for “greatest.”  The Almagest served as the primary astronomical and astrological text in the Western world as well as the Near East from the time of its inception around A.D. 150 until its astronomical content was first shaken by the work of Copernicus (1473-1543) and finally superceded by the work of Johannes Kepler (1571-1630) and Isaac Newton (1642-1727). 

While the Syntaxis was a brilliant treatise for its day, it suffers from the schematism so beloved by Aristotle that affected the intellectual life of the West for another thirteen centuries.  Among the main features of the Almagest that distinguish it from earlier astronomical models are that it employs geometric models (8) whereas the Babylonians used none, and the choice of time rather than position to locate a body in the zodiac. For the Babylonians all planet positions were based upon their places at critical moments: their synodic phenomena.  Once those positions in the zodiac had been determined, the Babylonians interpolated the positions of bodies between those phenomena to get accurate positions of the planets based on their regular behavior within their period relations.   Ptolemy addressed the question in the form: “Where are the planets at any particular moment in time?” with time rather than position as the independent variable.  Although the epicycle models Ptolemy used are not a true reflection of reality, and the solar system is heliocentric not geocentric, his numbers were close enough to correct that they were considered an acceptable approximation of the real world by the standards of his day.  The accuracy of the Ptolemaic model was shown to be quite imprecise, however, by the standard of the Western world 1300 years later.  He is still unquestionably the pre-eminent figure in astronomy/astrology in the West during Late Antiquity.

(1) Herman Hunger and David Pingree, “Mul.Apin An Astronomical Compendium in Cuneiform,” Archiv für Orientforschung 24, (1989): 12.

(2) The agreement in time between the dates of Jupiter’s stations over 427 years is much closer than it may first appear to be due to the different calendars in effect at the beginning of these two consecutive period relations.  The difference between twenty-first century Gregorian reckoning and sixteenth century Julian reckoning is thirteen days.  Thus the true difference between the beginning dates of Jupiter’s stations in 1580 and the 2007 is actually two days rather than fifteen.


(3) Declination is the distance north or south of the celestial equator measured in degrees of arc.  It is directly analogous to terrestrial latitude extended out into space.  The celestial equator is the plane of the Earth’s terrestrial equator extended off the planet into space.

(4) Celestial latitude is the distance north or south of the ecliptic plane measured in degrees of arc.  The ecliptic is a plane that intersects the centers of the Sun and the Earth that is inclined to the plane of the Sun’s equator by 7¼ °.  All the planets orbit the Sun approximately in the plane of the ecliptic except Pluto whose orbital plane is inclined to the ecliptic by 17°

(5) Bernard R. Goldstein and Alan C. Bowen, “The Introduction of Dated Observations and Precise Measurement in Greek Astronomy,” Archive for History of Exact Sciences 43 (October 1991): 114.

(6) G.J Toomer, Dictionary of Scientific Biography, s.v. “Hipparchus” (New York: Charles Scribner’s Sons, 1978): 15, Supplement 1, p.218.

(7) W.M. Smart, Textbook on Spherical Astronomy, 4th ed. (Cambridge: Cambridge University Press, 1960), 226.


(8) The epicycle theory of Apollonius of Perge that postulates planets in circular orbits around points which are themselves in circular orbits around the Earth.  Ptolemy’s explanations of astrological rationale and interpretation as explained in the Tetrabiblos are superb and well worth serious study even today.

© Kenneth Bowser, 2007. Adapted from An Introduction to Western Sidereal Astrology (AFA, 2012) To purchase the new edition of this book on, click here

Part Two will address the astrological ages; the Dark Age in the West after the collapse of Roman power in the 5th century and its affect on astrology; and how tropical astrology gained ascendancy in the West.

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