Astrological Systems (21.9.2026)

AI:

Yes. And the connection is actually fundamental: the four cardinal signs of the zodiac begin precisely at the astronomical turning points of the year.

Aries → vernal equinox, around 20./21. March

Cancer → summer solstice, around 20./21. June

Libra → autumnal equinox, around 22./23. September

Capricorn → winter solstice, around 21./22. December

That is because the tropical zodiac normally used in Western astrology is aligned with the seasons. By definition, 0° Aries is the vernal point. From there, the zodiac is divided into twelve sections of 30° each. That is why 0° Libra falls exactly on the autumnal equinox.

And with that I need to correct my previous answer: in 2026, astronomical autumn begins in Germany on 23. September, and at that very moment the Sun also enters Libra. So it is not that ‘Libra happens to begin on the 23. this year as well.’ Astronomically, both refer to the same point in time.

The calendar date can vary from year to year because a solar year is not exactly 365 days long. Depending on the year, the Libra ingress therefore falls on 22. or 23. September (and in some time zones possibly on an adjacent date), not invariably on 23. or 24.

Incidentally, this has a beautiful consequence for astrological symbolism: Libra really is the sign of the transition from the lighter to the darker half of the year. At the Libra point, day and night are approximately equal in length; after that, night increasingly gains the upper hand in the Northern Hemisphere. So your association today between Libra, the beginning of autumn and the dark season ahead is not merely astrological symbolism; it has a very concrete astronomical basis.

AI:

This is precisely where popular criticism often conflates two different things under the same term ‘zodiac sign’: zodiac signs and constellations.

Astronomically, the criticism is initially correct: the constellations have shifted relative to the vernal point. The cause is the precession of Earth's axis. Earth's axis wobbles very slowly like a spinning top; a complete cycle takes about 26.000 years. As a result, the vernal point moves relative to the fixed-star sky by roughly 1° in 72 years. Since antiquity, this amounts to a shift of almost one whole zodiac sign.

But the tropical zodiac predominantly used in Western astrology does not define its signs by the present-day positions of the constellations in the first place.

It works geometrically:

Vernal point = 0° Aries
→ 30° later = 0° Taurus
→ another 30° = 0° Gemini
→ …
→ autumnal point = 0° Libra

Because of precession, 0° Aries therefore cannot ‘move away’ from the vernal point. By definition, it is the vernal point.

The constellation Aries, on the other hand, can indeed move away from it—and that is exactly what has happened.

Historically, however, it becomes more interesting. Originally, the signs and the constellations after which they were named roughly coincided. In the 1st millennium BCE, the Babylonians developed a zodiac consisting of twelve equal 30° sections. The actual constellations, by contrast, are neither exactly 30° wide nor evenly distributed. In Hellenistic astrology, this eventually became the system from which Western astrology emerged.

The criticism based on precession is therefore not entirely nonsensical. It points to a historical and conceptual question:

> If the astrological meaning of ‘Aries’ originally had something to do with the stars of the constellation Aries, why should that same meaning continue to apply to the vernal point after the constellation and tropical sign have moved apart?

There are different astrological answers to this. Tropical astrology essentially says that meaning derives primarily from the annual Sun–Earth cycle, not from the fixed stars. Sidereal astrology—many forms of Indian astrology, for example—keeps the zodiac oriented to the stars and therefore accounts for precession by applying a corresponding offset (ayanamsha).

And this is where your earlier observation becomes genuinely interesting. If one accepts the logic of the tropical system, the classical symbolism acquires a remarkable internal structure:

Aries: light begins to gain the upper hand → departure, initiative
Cancer: maximum light reached → turning point, turning back
Libra: light and darkness in balance → equilibrium, counterpart
Capricorn: maximum darkness reached → concentration, limitation

They are then followed by fixed and mutable signs, which in a sense stabilize and dissolve these seasons again.

But this also means something that is often overlooked: this seasonal rationale is Northern Hemispheric. In Australia, spring rather than autumn begins at 0° Libra. That is one of the more interesting conceptual questions for a tropical astrology grounded consistently in the seasons.

In short: ‘The zodiac signs have shifted’ is astronomically correct if it means the constellations in relation to the seasons. It is wrong if the conclusion is that the tropical zodiac has accidentally lost its position. The tropical zodiac is deliberately anchored to the equinoxes and solstices.

And that is exactly why your question is so central: ultimately, it leads to the question of what an astrological sign is actually supposed to be—a section of the starry sky or a phase in the Sun–Earth cycle? Those are two different astrological models.

AI:

No—and this is where an interesting surprise lies: sidereal astrology, too, normally divides the zodiac into twelve signs of exactly 30° each. So it does not simply reproduce the actual constellations either.

The difference lies instead in where 0° Aries is set.

In the tropical zodiac:

0° Aries = vernal point.

Because of precession, this point moves relative to the fixed-star sky, but the tropical zodiac moves with it. The Sun therefore always remains at 0° Aries at the beginning of spring.

In the sidereal zodiac, by contrast, a reference to the fixed-star sky is chosen. From this starting point, twelve equal sectors of 30° each are then formed:

> 0–30° Aries → 30–60° Taurus → 60–90° Gemini → etc.

But the actual constellations look nothing like this. They vary in size. For example, the Sun spends considerably longer in the astronomical constellation Virgo than in Scorpio. In addition, the ecliptic also passes through the constellation Ophiuchus, the Serpent Bearer.

So three different things really have to be distinguished:

System Division Reference point

Tropical zodiac 12 × 30° Vernal point / seasons
Sidereal zodiac 12 × 30° Fixed-star sky
Astronomical constellations different sizes actual IAU constellation boundaries

Today there is a difference of about 24° between the tropical and sidereal zodiacs—the exact value depends on which sidereal reference system or ayanamsha is used.

That creates a substantial difference in a natal chart. Your Sun, for example, is tropically at about 8° Libra in early October. Subtract roughly 24° and it ends up sidereally at about 14° Virgo. Many planets change signs accordingly, while some remain in the same sign because of their position.

This also makes the often-heard astronomical criticism ‘You aren't really a Libra at all; you're a Virgo’ somewhat skewed. Astronomically, one could determine which actual constellation the Sun occupied. Sidereally, one could assign it to a 30° sign. Tropically, your Sun is in Libra. These are three different coordinate systems or definitions, not three competing calculations of the same thing.

That is precisely what makes the matter philosophically fascinating: sidereal astrology is not simply ‘astrology based on the real constellations’ either. It retains astrology's abstract twelvefold geometry and merely shifts its anchor from the seasonal cycle to the fixed-star sky.

AI:

The word ‘tropical’ actually has nothing to do with the tropics in today's sense of a hot climate—although both words have the same linguistic root.

It comes from the Greek τροπή (tropḗ) = ‘turn’, ‘reversal’, ‘turning point’.

What is meant are the turning points in the Sun's annual course. The two solstices show this especially clearly:

0° Cancer → summer solstice

0° Capricorn → winter solstice

This is also the origin of the geographical tropics: Tropic of Cancer = northern tropic and Tropic of Capricorn = southern tropic. When these names arose, the Sun occupied the corresponding tropical sign at each solstice.

The tropical zodiac could therefore also be understood as the ‘zodiac of the turning points’ or, more broadly, the ‘zodiac of the solar year’.

And this makes what we have just been discussing surprisingly clear in linguistic terms: its name already tells us that this system is fundamentally oriented to the annual Sun–Earth cycle, not primarily to the constellations.

In that respect, ‘tropical’ is actually a remarkably precise name.

AI:

Yes. It really could—and it would be a third system corresponding to neither the tropical nor the usual sidereal zodiac.

The twelve astrological zodiac signs also have corresponding astronomical constellations: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. Astronomically, however, Ophiuchus, the Serpent Bearer, must be added: the ecliptic also runs through this constellation, and the Sun passes through it.

The boundaries are precisely defined

In 1930, the International Astronomical Union (IAU) formally defined the boundaries of all 88 constellations. Every point in the sky therefore belongs unambiguously to exactly one constellation.

For a time of birth, one could therefore calculate astronomically:

> At that time the Sun was at this right ascension/declination or ecliptic position → this point lies within the IAU constellation Virgo.

The same could be done for the Moon, Mercury, Venus and so on.

The result, however, would be a rather unusual ‘natal chart’, because the sections would not be 30° wide. Along the ecliptic, the constellations vary considerably. Virgo and Scorpio are particularly striking examples: the Sun spends roughly a month and a half in Virgo, but only about a week in Scorpio. Ophiuchus then follows for the Sun.

For the Sun, this gives approximately the following astronomical sequence:

Capricorn → Aquarius → Pisces → Aries → Taurus → Gemini → Cancer → Leo → Virgo → Libra → Scorpio → Ophiuchus → Sagittarius → Capricorn.

Strictly speaking, that would give us a 13-part astronomical ‘zodiac’.

But with a complete natal chart, things become even more interesting

For the Sun, the matter is relatively simple because by definition it lies on the ecliptic. The other planets, however, lie somewhat above or below the ecliptic because of the inclinations of their orbits. The Moon and Pluto can deviate even more strongly from it.

If one truly used the IAU constellation boundaries, one would therefore not simply ask:

> ‘On which section of the ecliptic is Mars?’

but rather:

> ‘In which two-dimensional region of the sky is Mars actually located?’

The IAU boundaries are unambiguously defined for this as well. Consequently, two planets with very similar ecliptic longitudes could astronomically belong to different constellations because their ecliptic latitudes differ.

That would be fundamentally different from an astrological natal chart. There, the planets are essentially projected onto the ecliptic and assigned to one of the twelve signs on the basis of their ecliptic longitude from 0–360°.

And this is where an exciting possibility emerges for your RadixChat project

Alongside

Tropical: 12 × 30°, 0° Aries = vernal point

and

Sidereal: 12 × 30°, anchored to the fixed-star sky

one could add a mode

Astronomical: actual IAU constellations

and implement it.

Instead of ‘Sun 8° Libra’, for example, the result would be something like ‘Sun in the constellation Virgo’. The statement ‘8° Virgo’ would initially have no natural meaning at all, because an IAU constellation is not a 30° sector. A separate coordinate measure would have to be defined, such as the position within the section of the constellation traversed by the ecliptic.

This also shows once again why the claim that ‘astrology uses the wrong zodiac signs’ falls short. Astronomers certainly have precisely defined constellations. But neither of the two major astrological systems simply claims to use these 88 astronomical regions of the sky as its zodiac signs.

A horoscope constructed from the actual constellations would therefore not be a ‘corrected’ tropical horoscope, but a new or fundamentally differently defined astrological system.

AI:

Yes. And interestingly, this is by no means merely a modern internet idea. There really have been astrologers who tried to build exactly what we have just been discussing: an astrology more closely oriented to the actual astronomical constellations.

One important modern attempt came from Steven Schmidt, who in 1970 published Astrology 14. He even posited 14 signs, adding both Ophiuchus and Cetus (the Whale). In 1995, Walter Berg developed The 13 Signs of the Zodiac, a system explicitly based on the IAU constellation boundaries established in 1930. His system became fairly popular for a time, particularly in Japan.

Berg actually does roughly what we have just worked out in thought: the signs have different lengths. In his IAU-based system, for example, the Sun passes through Virgo roughly from 16. September to 30. October, Scorpio only from about 23. to 29. November, and Ophiuchus from around 29. November to 18. December.

And, surprisingly, Ophiuchus already has an ancient astrological symbolism

I find that even more fascinating.

Ophiuchus means ‘Serpent Bearer’. It is depicted as a man holding or wrestling with a serpent.

Mythologically, the figure is often identified with Asclepius, the great healer of Greek mythology. And from this emerges an exceptionally powerful symbolic world:

Serpent – poison – remedy – illness – healing – death – rebirth.

This is not an association invented retrospectively for ‘13-sign astrology’. The Roman astrological author Manilius already described Ophiuchus in his Astronomica and associated the figure with mastery over snakes and their venom. An astrological text from the 4. century linked the bright star Ras Alhague in Ophiuchus with physicians and healers.

Modern Ophiuchus systems have then developed from this an archetypal field of meaning, roughly:

Healing – transformation – handling dangerous forces – hidden knowledge – crisis and regeneration.

What is interesting, however, is that no astrological doctrine of the sign developed over thousands of years exists for it that would be comparable to that of Aries, Taurus and so on. As soon as someone makes Ophiuchus a fully fledged 13. sign and gives it personality traits, an element, a ruling planet and so forth, they begin constructing a new astrological model. Schmidt and Berg, for example, proposed Pluto as its ruler.

And for your thought experiment, I would make a distinction here that I find very appealing:

There would be no need to immediately and artificially saddle Ophiuchus with an ‘element’ or a complete personality doctrine. One could initially proceed just as you have repeatedly argued in relation to Lilith and Chiron: first examine the archetype carefully, and only then develop astrological meanings from it.

With the Serpent Bearer, the archetype would be unusually rich. He does not destroy the serpent. He holds it. The dangerous thing is in his hands. The same poison can kill or—properly dosed—be medicine.

As an astrological principle, that would be something different from, for example, Scorpio's theme of death and rebirth or Chiron's wounding and healing. Ophiuchus might stand more for the ability to deal consciously with a potentially destructive force and transform it into something healing.

And then something else becomes very interesting: if we truly wanted to construct an astronomical natal chart, we could not simply replace twelve signs with thirteen. We would have to be consistent: actual constellation boundaries, different sizes, a planet's real position including ecliptic latitude—and then investigate whether a coherent astrological system of interpretation could emerge from it at all.

That would be far more radical than sidereal astrology. It would genuinely be a kind of ‘constellation astrology’. And Berg is one of the few who went quite a long way in precisely this direction.

AI:

Yes. And your sense of a certain contradiction touches on something historically interesting: it appears that the 30° signs arose precisely because the actual constellations were too unwieldy for precise astronomical calculations.

The history can be reconstructed quite well.

At first, there were no twelve equal boxes

The Babylonians initially observed actual stars and stellar configurations along the path of the Moon and planets. MUL.APIN, a Babylonian collection of astronomical texts, still contains a list of stars or constellations on the ‘Path of the Moon’. These formations were, of course, different sizes.

Then, around the 5. century BCE, something decisive happens: this observed sky becomes a mathematical coordinate system.

The ecliptic is taken as a complete circle:

360°

and this is divided into:

12 × 30° = 360°.

The earliest surviving evidence for such a 360° zodiac dates from after about 450 BCE; the historian of science Mathieu Ossendrijver dates its introduction to roughly this period.

And the remarkable thing is that researchers do indeed interpret this equal division as a mathematical idealization, not as a claim that the constellations are in reality equal in size.

Why exactly 12 × 30?

There is a highly plausible explanation, although it cannot be proved conclusively.

The Babylonian schematic calendar used 12 months of 30 days each. The ideal year therefore had:

12 × 30 = 360 days.

The Sun travels once around the ecliptic in roughly a year. It is therefore extremely natural to divide the Sun's path into 12 × 30 units as well. This connection between calendar and zodiac is explicitly discussed in current research.

Then there is the Babylonian sexagesimal system, mathematics based on 60. Within it, 360 is an exceptionally convenient number: it is divisible by 2, 3, 4, 5, 6, 8, 9, 10, 12 and so on.

This yields an almost ingenious coordinate system:

> Mars is no longer somewhere ‘toward the back of Leo’, but, for example, at 17° Leo.

Suddenly, movements can be described mathematically, tables compiled and future positions calculated. Babylonian planetary tables from around 400–50 BCE use precisely this system of twelve 30° signs.

And this resolves your apparent contradiction

What you are saying, in effect, is this: first a completely abstract 30° division is defined, and then planetary positions within it are determined to the exact minute. That seems strange.

But that is exactly how coordinate systems work.

Take our geographical coordinates. The 8. degree of longitude is not visible on the ground. There is no natural boundary there. The Greenwich prime meridian is a human convention.

Nevertheless, we can say:

50,9413° N, 6,9583° E

and use it to describe a location with extreme precision.

The abstraction of the coordinate system therefore does not conflict with precision. It is what makes precision possible in the first place.

And that was evidently the great achievement of the Babylonian zodiac. The historian of science Francesca Rochberg describes the transition, in essence, as follows: once the signs were defined by degrees of longitude rather than by the actual boundaries of the constellations, they became an astronomical and numerical reference system.

However, this raises a much more intriguing question for astrology

Up to this point, we have not really been talking about astrology at all, but about astronomy and mathematics.

One could simply say:

> We divide the ecliptic into twelve equal sections so that we can calculate.

But this does not explain at all why, for example, the section from 0–30° should possess an Aries character.

And this, in my view, is where the truly interesting historical question behind your unease begins.

Originally, the names and images came from the actual stellar constellations. The mathematical zodiac adopted those names, but turned them into equal-sized regions.

Later, a further development was added: eventually, the tropical zodiac was anchored to the vernal point.

So we really have three historical layers on top of one another:

1. Observed sky
There are actual stars and constellations of different sizes.

↓

2. Babylonian mathematical abstraction
They become twelve equal 30° coordinate regions.

↓

3. Tropical definition
The entire 12×30° grid is coupled to the annual cycle:
0° Aries = vernal point,
0° Cancer = summer solstice,
0° Libra = autumnal point,
0° Capricorn = winter solstice.

Only through this does the tropical system acquire the strong seasonal symmetry we were just discussing.

This also changes something for me about the question ‘But the constellations have shifted’. Historically, the truly difficult question is not:

‘Was precession overlooked?’

but:

‘Where does the meaning of a sign actually come from?’

From the original constellation?
From its place within the twelvefold circle?
From the season?
From millennia of astrological meaning-making?
Or from a combination of these?

There is no longer an astronomical answer to that. It is a question within the astrological model.

And after our conversation, I also understand better why the astronomical-constellation variant is currently more repellent than appealing to you. It would not merely correct a few positions. It would replace the entire grammar with which you have thought astrologically for decades.

What is remarkable is that the 30° division is by no means some sloppy historical approximation that modern astronomy could now make more precise. Its uniformity was the whole point of the invention from the start. It was precisely the step from the irregular starry sky to a calculable model.