Skyscript home page


For and Against: The Zodiac Debate

One topic that is sure to cause controversy amongst astrologers is that of whether the Tropical or Sidereal zodiac is most effective in practice. A recent forum debate revealed how passionately astrologers cling to alternate views. In 1997 the Traditional Astrologer magazine asked two expert astrologers to justify their own choice by reference to history, philosophical logic and the results of their own experience. Their responses have been reproduced here and allow us to consider the historical influences upon this 'astrological complication' in-depth.

This debate assumes a knowledge of the issues connected to precession. For a more detailed explanation of precession and the early refinement of zodiacal signs refer to the article Heavenly Imprints.

For The Tropical Zodiac - David McCann

In recent years certain astrologers have made two assertions that I would like to examine and, hopefully, refute. The first is that ancient astrologers used a sidereal zodiac; the second is that this, if true, implies that we should adopt one. The best answer to the assertion that the ancient zodiac was sidereal is a question: which zodiac? The zodiac was involved in chronometry, astronomy, and divination. These make conflicting demands, for chronometry implies a tropical zodiac but astronomy a sidereal one! Reconstructing the history of the zodiac is not easy - only a fraction of ancient writings have survived and 90% of Mesopotamian texts still lie unpublished in museum basements - but the following account is probably not too far from the truth.

The desire to produce an accurate calendar was one of the earliest motives for studying the sky. Once agriculture started, particularly if it involved irrigation, a reliable calendar was needed to plan the activities of the farming year. The Greeks and Romans, with fairly useless calendars, continued to depend upon observing the heliacal risings and settings of stars:

But when beneath the skies on morning's brink
The Pleiads, Hyads, and Orion sink,
Know then the plough and seed-time near.

(Hesiod: Works and Davs, transl. Elton)

The more reliable calendars of the Near East were linked to the seasons and so agricultural operations could be regulated by the months. To do this it was necessary for the year to begin with the first lunation after a solstice or equinox, and so a constellation had to be identified which marked the 'cardinal point'. This was done at a very early date: both the Babylonians and Indians long preserved memory of the time when the spring equinox was marked by the Pleiades, around 3000 BC. The creation of a series of twelve constellations to match the twelve months naturally came later. If the cardinal signs were meant to locate the cardinal points, one would not expect to find the points at the beginnings of the signs but in the middle. The tradition that they fell at 15° was preserved by Eudoxus, although in his day they were actually at 8°. Extrapolating back from later figures, we can place the origin of the calendrical zodiac with the cardinal points in Aries, Cancer, Libra, and Capricorn to sometime after the 9th century BC.

To understand the role of the zodiac in early astronomy consider how one would set about measuring the position of a planet. Today we would use a telescope in an accurately-calibrated equatorial mounting to find the planet's altitude and azimuth (compass-bearing) and then, given the correct sidereal time, its latitude and longitude could be calculated. The ancient astronomer needed a simpler approach, and so measured the difference in co-ordinates between the planet and the closest known star. The Babylonians eventually developed a set of 31, (known today as the 'normal stars'), from which all observations were measured. The planetary observations given by Ptolemy in the Almagest were similarly located with respect to a few well-known stars. In his instructions for constructing a celestial globe, Ptolemy recommended that all longitudes should be measured from Sirius, so that it would not become out of date as a result of precession. The Babylonians established a standard set of 18 constellations along and around the ecliptic as early as the 2nd millennium. Those outside the zodiacal belt were useful for orientation: Perseus is far easier to recognise than Aries. These original constellations were not equal in size, and were presumably re-described when they were reduced to twelve and matched to the calendrical zodiac. Fixed stars continued to be used as reference points throughout the Middle Ages, and even Copernicus measured positions in a sidereal zodiac beginning from the fixed star Mesartim.

So which zodiac did the ancient astrologers consider themselves to be using, the tropical or the sidereal? The most probable answer is that they didn't know the difference. If we examine the surviving Greek and Roman writers on astronomy, we find that most showed no awareness of precession: Geminius, Cleomedes, Theon of Smyrna, Manilius, Vitruvius, Pliny, Columella, Censorius, Achilles Tatius, Chalcidius, Macrobius, and Martianus Capella. Some of these, (eg., Manilius, Pliny, Achilles), mentioned the various positions which had been given for the cardinal points in the astronomical zodiac, but regarded this variation as a dispute among astronomers - they showed no indication of realising that these were all correct positions, but at different dates. Most authors continued to place the cardinal points in 8° of the sidereal signs, the position correct for the 4th century BC when astrology was first disseminated in Greece. Only Hipparchus, Ptolemy, Theon of Alexandria, and Proclus were aware of precession, and Proclus didn't believe in it! Theon and Proclus also recorded the alternative theory of 'trepidation', later common among the Arabs and Indians: the idea that the cardinal points oscillated over an arc of 16°. When scholars like Pliny and Proclus were ignorant, is it likely that working astrologers were any better informed? How much astronomical knowledge does the average modern astrologer have? The practical effect of this confusion was of little real importance. During the Roman period, the few degrees error produced if the wrong zodiac were used would have no more effect on chart interpretation than the frequent errors of similar magnitude in calculating planetary longitudes.

Even if precession was of little consequence to Roman astrologers, it had been instrumental in the discovery of the astrological zodiac. Although the background of astrology is Mesopotamian, the concept of continuous influences rather than sporadic omens seems to belong to the world of Greek philosophy, and the numerical structure of the aspects suggests the influence of Pythagoras. He died about 500 BC and contacts between Greeks and Babylonians would have increased at this time, following the Persian conquest of the Ionian Greeks and the settlement of many Persians and Babylonians in that area. The oldest surviving horoscope, from Babylon, dates from 410 BC, so true astrology probably developed in the fifth century. At this time the cardinal points were around 9° in the sidereal signs. This means that sign positions in the tropical and sidereal zodiacs showed a 70% correspondence. Can it be a coincidence that meanings were not attributed to the zodiacal constellations before this period? It surely implies that the astrological zodiac is tropical and that it was discovered by chance as the two zodiacs came to coincide. By about 260 BC Aratus placed the cardinal points at 0° even though they actually fell at 7° in the sidereal signs: his zodiac was tropical, or rather, the astrological zodiac had taken its place alongside the astronomical one.

Just as precession revealed the existence of the astrological zodiac, so the failure to understand it could lead to it being lost again. As the sidereal and tropical zodiacs moved out of alignment, so the former lost astrological significance. In India the interpretative use of the sidereal signs survives only in the case of the ascendant: this, however, is not to delineate an ascendant based on a timed chart, but to choose the sign of the ascendant as the first stage of rectification. Modern Western siderealists, who in theory give the same meanings to the signs as the rest of us, in practice largely ignore them in delineation.

The view that if the Ancients had been siderealists we would have to follow suit, is difficult to understand. It seems to come from viewing ancient astrology as a closed system which sprung into existence fully-developed and which could never progress, only degenerate. But this view can only he held if we close our eyes to history. If we are to return to the 'Magi of Chaldea', then astrology as we know it must be abandoned: the Enuma Anu Enlil is not a book of astrology, but of celestial augury. To return to the Babylonians is to abandon the houses, the zodiac, all aspects other than the conjunction, the very horoscope itself. We could, of course, try to reconstruct the first system of true astrology, but we would soon find ourselves aiming at a moving target. Modern siderealists seem to be taking this approach when they adopt what they consider to have been the original zodiac and reject the interpretative rise of the houses, yet they still employ many techniques which were unknown to the first astrologers, such as returns and directions.

One does not need an uncritical belief in progress to accept that discoveries could be, and have been, made. Similarly, mistakes could be made. The Greeks, no doubt deriving the view from the Babylonian use of bodily conjunctions, believed that aspects should be measured from body to body and, in consequence, that two planets could not be in partile conjunction if they differed in latitude. Modern experience shows that Pluto makes conjunctions with 17° of latitude, when tradition would rule out even a platick aspect. Cyril Fagan, seeking a golden age of astrology among ancient priests, was as much mistaken as Gauquelin seeking it among future physicists. There is no golden age, with astral priests or natural scientists to solve our problems for us: only we astrologers, pursuing our art as best we can in the here and now.

The real question is not which zodiac the Ancients used, or thought they used, but which works. Does the sidereal zodiac work? Move your ascendant and lights back 25° and then draw your own conclusions. As I observed above, all astrologers use the same meanings for the signs, despite assertions to the contrary by some siderealists. All describe Scorpio as intense, wilful and determined, yet most of our Scorpios are classed as Librans by the siderealists! Either they spend too much time talking about astrology and not enough time doing it, or they just lack any understanding of human nature. Either way, I find it impossible to take them seriously.

 Next: The Case for the Sidereal Zodiac by Ken Bowser

If you wish to comment on this debate, you can add to the thread in the forum where the tropical v. Sidereal issue is being discussed.

David McCann, who lives in London, is an expert on the history and philosophy of astrology. His articles have been published in many international journals of astrology and he was a regular contributor to the Traditional Astrologer magazine, where this article first appeared.

© David McCann. Published online February 2005. First published in The Traditional Astrologer magazine, (Ascella), Issue 14, May 1997, pp.23-27

For the Tropical Zodiac: David McCann

  Now read the case for the Sidereal Zodiac by Kenneth Bowser