Kenneth Bowser


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An Introduction to Western Sidereal Astrology

By Kenneth Bowser


In January 2011 Parke Kunkle, a Minnesota community college instructor, ignited a national firestorm of controversy in the astrological community when he pointed out that the signs of the zodiac no longer correspond to the constellations of the same name.  This issue has been vigorously debated by astrologers for the last sixty-five years. 


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. The term tropical, from the Greek τροπικος (tropikos, a turn or turning), refers to the Tropics of Cancer and Capricorn that describe the limits of the tropics.  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 from the Latin sidus (star) 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. Sidereal astrology is the original form of the art.  Its antecedents date from mid second millennium B.C.; it gained currency in the Near and Middle East in the first 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. 


The difference between tropical and sidereal reckoning is due to the phenomenon of precession of the equinoxes which is explained in detail in Appendix Two.   The word “precession” derives from the Latin verb praecedere, to precede. Precession, as used here, refers to the gyration of the rotation axis of a spinning object like a child’s spinning top. The Earth’s spin axis precesses in the same way. Precession of the equinoxes refers to the slow westward motion of the solstitial and equinoctial points along the ecliptic.  The term “precession of the equinoxes” was first used by Copernicus (1473-1543).

The Greek genius and best-known astronomer of his day, Hipparchus of Rhodes (flourished 146 – 127 B.C.), is credited with the discovery of precession.  His work on precession is lost except for the title, “On the Displacement of the Solstitial and Equinoctial Points,” details of which are mentioned in Claudius Ptolemy’s Almagest, the most important astrological and astronomical work of Late Antiquity.  Hipparchus’ only work that has survived intact is the “Commentary on the Phaenomena of Eudoxus and Aratus.”  Ptolemy (≈ A.D. 100 – 175) is the main source of other works by Hipparchus. 

By comparing his own contemporary observations of stars with older positions of the same stars, Hipparchus noted a difference in their distances from the equinoxes.  Specifically he noted that Spica, the brightest star in Virgo, was observed eight degrees east of the autumnal equinox 150 years before his time, but only six degrees east of the autumnal equinox in his own time (which is a westward motion of the equinoxes).  The case has been made by G. J. Toomer* that Hipparchus 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 Hipparchus’s determination of the difference between the tropical year and the sidereal 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 probably, Professor Toomer thinks, the very end of Hipparchus’s career.  The false speculation of a regular eight degree oscillation of the equinoctial points called trepidation, sometimes attributed to Hipparchus, is actually from the 4th century A.D.  Another modern authority with impressive astronomical and academic credentials also maintained that Hipparchus 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 Hipparchus compared 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.**

There is no solid evidence that Hipparchus invoked the tropical zodiac but it is attributed to him primarily because of what Ptolemy wrote (three hundred years later) about the matter in his Almagest.  Regardless of Hipparchus’s positions which were various at different times in his career, the conclusion that eventually won out—one of several solutions proposed  to explain precession—was that the entire sky was moving as a unit against the Earth fixed in space. This was arrived at in part because Hipparchus (and later Ptolemy) couldn’t detect any motion between stars, rather only between the stars and the equinoxes.  Hipparchus’ probable final conclusion that the equinox had moved was not, however, the position that was adopted in the ancient world.  Rather, the hypothesis adopted by Ptolemy that the stars had moved was based on the fundamental assumption of his day that the Earth was motionless in space and the center of the universe. That is the basic tenet of geocentrism: the idea that all bodies orbit a fixed Earth.  If one sees motion between oneself and another object and one cannot detect oneself in motion, the conclusion is ineluctable: the other thing must be moving.  That is the ultimate result of the geocentric concept of solar system geometry embraced by the Greeks.  There was no experiment devised in Hipparchus’s or Ptolemy’s time that could demonstrate the motion of the Earth. Their geocentric assumptions were reasonable for their time.

If one views precession from the perspective of a motionless Earth, absolutely fixed  in space forever, the celestial longitude of the stars increases by slightly more than 50 seconds of arc per year, a degree of arc in almost 72 years and an entire thirty-degree sign in approximately 2150 years.  (Hipparchus had it nearly right; he proposed an increase of almost 46 seconds of arc per year, Ptolemy proposed 36 seconds of arc per year.)   Seen from the deeper and true perspective of the Earth in motion in several modes revolving around the Sun, the Earth’s celestial pole precesses and the equinoxes retrograde past the fixed stars with a period of 25,800 years.  This true perspective also accounts for the astrological “ages” (the Age of Aries, Age of Pisces, Age of Aquarius etc.) that are entirely sidereal phenomena and have nothing to do with tropical zodiac reckoning.

The displacement between tropical reckoning that appears to be fixed in space but is actually moving, and sidereal reckoning that appears to be moving in space but is actually fixed, is presently almost twenty-five degrees.  Since the northern hemisphere spring equinox moves to the West with respect to the stars, the sidereal signs are twenty-five degrees to the east of where they were described at the beginning of the Age of Pisces in A.D. 221. That apparent movement, however, is an illusion, not something real, as the stars have not moved in eighteen centuries except for a tiny handful of seconds of arc.  Within the framework of tropical reckoning the sky moves with respect to fixed civil dates; within the framework of sidereal reckoning, civil dates move with respect to the fixed stars.  Since the Gregorian Reform of the Julian calendar in 1582, the northern hemisphere vernal equinox usually occurs on March 21 that marks the entry of the Sun into the tropical sign Aries.  That date however has nothing to do with the stars in Aries during the present era.  If one could look at the stars behind the Sun on March 21, 2011 one would see the stars in the western fish of Pisces with the Great square of Pegasus above the zodiac and Cetus the whale below the zodiac.  The constellation Aries is far to the east of the northern hemisphere vernal equinox.  Twenty-five degrees is a massive expanse of sky.  People who actually look at the sky are astonished at the discrepancy between tropical and sidereal reckoning.  Presently in 2011, in terms of the twelve-fold equal division zodiac employed by the Babylonians, the Sun reaches Aries in most years on April 15. That means that at any location in either hemisphere where the Sun is visible on that date, if one could block out the Sun and look at the stars behind it one would see the stars in Aries with Triangulum and a corner of Perseus above the zodiac and Hydra and Eridanus below the zodiac.

It wasn’t always like this.  Tropical and sidereal reckoning were exactly coincident—completely identical—at the end of the Age of Aries in A.D. 221.  They were so close to being identical for so long that throughout the second and third centuries of the Christian Era nobody could tell the difference between tropical and sidereal reckoning without instruments and/or a marking star. 

Claudius Ptolemy wrote about what anybody would have seen in his day if they had gone outside at night with horoscope in hand and looked from the horoscope to the sky. The symbolic rendering of the zodiac on the horoscope would roughly duplicate the evidence of one’s eyes.  Yet Roman astrologers in Late Antiquity, and certainly during Ptolemy’s day, were clearly using a combination of outdated sidereal and inaccurate tropical standards that were merely approximate even by the standard of the day, much less modern standards.  The great majority of the positions of the horoscopes from the Roman world of Late Antiquity are sidereal from an earlier period and the tropical ones reckoned from an Hipparchan equinox (0° Aries = vernal equinox) are adjusted for precession (using Ptolemy’s grossly inaccurate value for precession) which betrays a lack of understanding of tropical reckoning.  A large proportion of Roman horoscopes from Late Antiquity also include the distance of a planet from a star that shows further sidereal influence and lack of confidence in an equinox unmarked by a star.  Tropical reckoning was much better established as a medieval standard than an ancient one.  Ptolemy’s account of the sky circa A.D. 140 when The Almagest was being written is not what one sees today.  The Sun rose with the first degree of Aries in Ptolemy’s lifetime as an astronomical fact.  Now in 2011 the Sun rises with five degrees of Pisces in an equally undeniable fashion. The Age of Aquarius will begin in A.D. 2376 when the Sun rises with 29° Aquarius 59' at the northern hemisphere vernal equinox.

The discrepancy of twenty-five degrees leads directly to a bigger issue—the ultimate issue actually—for an astrologer to consider: tropical reckoning un-couples the zodiac from the stars.  If the sky is defined by one set of criteria (the fixed stars) at one period and a different set at a later period (the equinoctial points), then identical calendar dates will not describe the same parts of the sky though both sets of criteria have the same name.  The issue is whether trait characteristics derive from the tropical signs or the sidereal signs.  A related matter, the question of how and why the tropical zodiac displaced the sidereal zodiac in the West is also explained in Appendix Two.

That these issues are debated at all among Western astrologers is due primarily to the work of Cyril Fagan (1896 – 1970) whose life from 1916 until his death was devoted to astrology.  He realized in 1944 after many years of study that the zodiac employed in the ancient world, before Greek influence was felt, was sidereal.  Fagan was originally a tropical astrologer who encountered intense resistance from British and American astrologers when he substituted sidereal zodiac parameters used in Babylon for a tropical zodiac format.  All subsequent siderealists in the United States and Europe cut their teeth on Fagan’s books, magazine columns and his open-ended debates with the leading tropical figures of the 1940s, 1950s and 1960s.  A more detailed explanation of Fagan and his work are in Appendix One.

I am one of those deeply influenced by Fagan’s work.  I became a student of astrology in 1970 as a tropicalist.   I met Jim Lewis (1941-1995) in 1972 who was just then getting his business, Astrocartography, off the ground.  His very interesting lectures to a dozen rookies seated on the floor of his spartan apartment were a tremendous stimulus to young enthusiasts hungry for information.  He was a lifelong tropicalist but he many times spoke of his respect for the siderealists for their technical skill.  In consequence of Lewis’ fair-minded attitude and ever curious myself, I attended a lecture given by a San Francisco siderealist, John Mazurek (1919–2003) also beginning in 1972.  I attended Mazurek’s lectures for three years and by the end of that time had defected from the tropical ranks.

Sidereal astrology attracted me for four basic reasons: first, I had problems reconciling what I had learned about the signs with what I observed in people like President Ronald Reagan who was a tropical Aquarius but a sidereal Capricorn.  As a long-time California resident I had observed Reagan since his rise to power in the mid 1960s as governor of California.  He didn’t appear to me to display Aquarian traits but the Capricorn qualities were quite marked.  There were a lot of people like Reagan in my experience who were spectacularly bad tropical fits but easy to see in a sidereal context.  Second, the tropical signs don’t even remotely correspond to the constellations that are their namesakes.  That fact spurred me to understand the facts behind the tropical-sidereal disconnect.  Third, sidereal solar and lunar returns were the best predictive technique I had encountered as an astrologer.  Fourth, I was fortunate to become acquainted with several outstanding members of the second generation of modern siderealists, most notably Arthur Blackwell (1942–1992) and Paul Schure (1948–2007).  They were by far the best interpreters I had met of any stripe and I wanted to understand their reasoning.

I set up and studied the horoscopes of everyone around me, attended lectures by renowned astrologers whenever possible and read the works of master astrologers, mainly Claudius Ptolemy, Abu Ma’sar, Guido Bonatti, William Lilly, John Worsdale, A. J. Pearce, Walter R. Old, W. J. Simmonite, Charles E. O. Carter, B. V. Raman and, of course, Cyril Fagan. In college I took every class that was directly or indirectly related to astrology from celestial navigation, astronomy, the histories of Egypt, India, Assyria, Babylonia, Greece and Rome to the Akkadian, Greek and Latin languages.

The book is not directed at any particular level of experience.  It will be of value to novices, intermediate and advanced students.  The first six chapters cover the astrological basics: planets, signs, aspects and houses.  The second section, which is the biggest section of the book, covers the forty-five planet combinations.  The third section deals with interpretation with specific illustrations of the horoscopes of well-known geniuses, politicians and notorious figures. There are three appendices. Appendix One is a brief history of the Sidereal Zodiac.  Appendix Two addresses the tropical – sidereal question.  Appendix Three addresses the exaltations.



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


**W. M. Smart, Textbook on Spherical Astronomy, fourth edition (Cambridge: Cambridge University Press, 1960), 226.  Smart wrote on page 226 about the annual increase in the longitudes of the stars observed by Hipparchus which were the same for every star:  “There are two possible explanations: either all the stars examined had real and identical motions in longitude – an improbable hypothesis – or the fundamental reference point, the vernal equinox Aries from which longitudes are measured along the ecliptic, could no longer be regarded as a fixed point on the ecliptic.  Now Aries is defined to be one of the two points of intersection of the ecliptic and the equator on the celestial sphere; the observations showed no changes in the latitudes of the stars and therefore it was legitimate to conclude that the ecliptic was a fixed plane.  According to the second hypothesis (which was adopted by Hipparchus [parentheses are Smart’s]), it was necessary to assume that the equator had moved and, in consequence, the vernal equinox moved in such a way that the longitudes of the stars increased uniformly by an amount in accordance with the observations.”

Excerpted from An Introduction to Western Sidereal Astrology, by Kenneth Bowser. Reprinted with permission by The American Federation of Astrologers.  © 2012 Kenneth Bowser. All rights reserved.