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What is Sidereal Astrology?

Updated: Jul 14, 2020

The Sidereal Zodiac is growing in popularity in the West, but it's still not a subject much taught in astrology classes. There's a lot of myths and misinformation in circulation, and plenty of smart, knowledgeable astrologers remain confused as to what Sidereal actually is. Clues: it's not Vedic, it doesn't use thirteen signs, and it's not even an attitude struck by modern astrologers in search of a unique selling point.

Short version

The Sidereal (meaning 'of the stars') Zodiac is measured from the fixed stars of the ecliptic constellations rather than the (Tropical) Vernal Equinox. It's a different concept of the zodiac to Tropical, one based on the actual stars rather than the seasons, even though its twelve equal 30° signs are interpreted in the same way. The Sidereal zodiac remains unmoving, while the Tropical zodiac shifts gradually backwards by a movement called 'Precession of the Equinoxes'. Today the two zodiacs are separated by a distance (Sanskrit term ayanamsha) of 24°, though they once coincided, back in the 3rd century AD. The Sidereal zodiac has always been used in India, but it was also the original Western (pre-Hellenistic) astrology which underwent a major 20th Century revival. The Sidereal paradigm is preferred for its vivid sign archetypes and accurate, precession-free timing for transits and returns.

Longer version

'Precession of the Equinoxes' is caused by the Earth's rotational wobble on its axis, where the Aries Point shifts slowly backwards, 1° degree every 72 years, for an entire cycle of 25,800 years (a period known as the Great Year). In the 3rd Century AD the moving Equinox came to a point in its cycle where it overlapped precisely with the fixed Sidereal stars, and for a century or so the two zodiacs became effectively one. At this point the Hellenistic scholar Claudius Ptolemy wrote an influential text, the Tetrabiblos, which identified the Vernal Point with 0° Aries; ie, the start of the zodiac. Before this point the zodiac was not defined by the Equinox. Ptolemy's interpretation was true for his own time, but not for all times.

After Ptolemy's time, some astrologers still used the original Sidereal zodiac while others took the new 'Tropical' system which identified 0° Aries forever with the Spring Equinox. By the time Ptolemy was translated into Latin in around the 10th Century AD, Sidereal had gone almost completely underground in the West, though it remained the dominant system in India. Precession - the backwards movement of the Equinoxes - was abandoned as a parameter and Western astrologers calculated horoscopes in a folkloric sense as if the year was forever 275 AD. Yet they still used the Sidereal signs; elements, qualities and symbolism, even though the Tropical signs no longer matched their original, organic positions. The fixed stars were treated as if they were moving rather than the shifting Equinoxes, and astrology became grounded and Earth-centric and lost touch with its original Sidereal ethos.

The above chart shows the ecliptic constellations around the outside in red, the Sidereal zodiac in the middle in yellow, and the Tropical zodiac in the centre in green. Tropical is oriented to the Equinoxes and Solstices, particularly the Vernal Equinox, March 21st, which is 0° Aries. Yet this convention in 2020 equates to 5° Sidereal Pisces, with 24° of precession having accrued since the Equinox lined up with the stars in the 3rd Century. The Royal Stars of the Sidereal zodiac are also shown, in the fixed signs, which remain unmoving in their positions for tens of thousands of years.

It is often said, 'Sidereal is based on the Stars, Tropical is based on the Seasons'. Ptolemy justified his new Tropical zodiac on the basis of the Northern Hemisphere seasons - Aries brings Spring Lambs, Leo sees the height of Summer, Capricorn Winter Solstice is the darkest and coldest time, etc. This symbolism is still invoked today, even though it doesn't apply in the Southern Hemisphere where the seasons are reversed. The Tropical zodiac remains useful for predicting weather and the turnings of the year, but it was never intended to plot the position of the planets and stars.

This historic 'two-zodiac' disruption in astrology continues up to the present time, where the systems are now 80% of a sign out of alignment and increasing year on year. Today most people have different tropical and sidereal signs, while others are the same in both systems - and in another 350 years the two zodiacs will be a whole sign apart. It's as if one instrument is calibrated in two different ways, but both give the same result: logically, both systems can't be right.

The 'fixed stars' that orient the Sidereal zodiac are chiefly the Persian Royal Stars: Regulus (5° Leo), Aldebaran (15° Taurus), Antares (15° Scorpio), and Fomalhaut (10° Aquarius). The axis of Aldebaran in the centre of Taurus (The Eye of the Bull) and Antares in the centre of Scorpio (The Heart of the Scorpion) is a particularly important Western Sidereal reference point. The guiding star in the Vedic system is Chittra (Spica) at 0° Libra, exactly opposite to the Vernal Point - Chittra/Spica is used because there are no first-magnitude stars in Aries itself.


I thought Sidereal was Vedic Astrology?

Vedic astrology has always used the sidereal zodiac, but sidereal is not Vedic per se. Even though Vedic sign-lore has a great deal in common with the West - signs, symbols, elements & qualities - Vedic and Sidereal are not synonymous terms.

Does Sidereal use 13 signs?

This perennial red herring comes up whenever there is a slow news day and is guaranteed to stir the blood of any halfway-knowledgeable astrologer. The sidereal zodiac is an energy mandala oriented to the fixed stars, not a literal map of the modern constellations. Astrologers have always known the constellation Ophiuchus cuts into the ecliptic plane, and integrated its Serpent-Bearer symbolism into the zodiacal sign of Scorpio. There are 12 signs by definition of every culture that has ever used the zodiac: Babylonian, Egyptian, Persian, Greek, Roman, Indian.

Sidereal and Tropical signs must be interpreted differently?

Actually no, both zodiacs are based on the original Babylonian sidereal archetypes: Aries is the Ram and cardinal fire , Taurus is the Bull and fixed Earth, Airy, Gemini is the Twins and mutable Air, and so on, identical in both systems. Some blurring of the lines has occurred where astrologers observe traits belonging more to a previous sign, for example, Sagittarius's wounding honesty is actually Scorpio's 'sting in the tail'; Libran fastidiousness has more to do with Virgo; Taurus has become notorious for its temper, when this is actually an Aries trait, while Aries are said to be 'sacrificial lambs', because today they are mostly sidereal Pisceans. The fundamentals are the same, however, and sidereal gives noticeably sharper and more classical, textbook sign depictions.

Yes, but the constellations aren't really equal:

A constellation is not a sign, the definition of which is a 1/12th equal portion of the ecliptic. The concept of a sign is far older than the unequal divisions of the sky today, certainly older than the list of modern constellations authorized by the International Astronomers Union in the 1920s. Rather than man-made the Sidereal zodiac is a man-discovered field of energy existing in nature.

Yes but the fixed stars are also moving.

The average 'proper motion' of the fixed stars is 1° every 120,000 years - that is a period twenty times the length of recorded human history to move a single degree. They are comfortably fixed for you and me and the next six thousand generations of astrologers. The relatively quick motion of the Equinoxes on the other hand creates the illusion of stellar movement, like for example the royal star Regulus appeared to have moved into Virgo in the early 21st Century. Of course the aprecessional sidereal Regulus ('The Heart of the Lion') remains at 5° Leo for many thousands more years, and in Leo altogether for millions more years. 

Moreover, the sidereal zodiac is an energy matrix that is fixed in space for all time and exists irrespective of any one fiducial star or stars.

But Tropical signs clearly work.

Does anyone ever question their tropical zodiac signs, on first sight? Not much, it seems. Sidereal is very rarely taught in beginner's classes and this overwhelming Tropical bias at a tender stage of development makes its sign-lore very difficult for astrologers to un-learn. It is a heavily-invested self-fulfilling prophecy that tropical signs 'work'.

Yes, but there are so many different 'ayanamshas'.

This situation is not ideal, yet it's also an objection that tends to be exaggerated. In the real world, practically every Western Sidereal astrologer uses Fagan-Bradley and the great majority of Jyotishis use the Indian Government-approved value, Lahiri. These two ayanamshas differ by about half a degree.

Is Sidereal your past life?


How can centuries of tropical astrologers have been wrong? 

Tropical reckoning hasn't always been so far awry; precession is incremental. In the 17th century, the ayanamsha was 2/3rds of a sign, now it is 4/5ths. A Renaissance master like William Lilly for example, was famous for Horary Astrology, a more purely divinatory branch of the art concerned principally with applying aspects. Horary, arguably, is less dependent on specific signs than a quasi-magical attitude which, along with experience and human genius, will give good results, if in spite of its zodiac rather than because of it.

Is the zodiac debate only about sign-traits?

No. Precession also affects the timing of transits and particularly (Solar) returns. For example, sidereal Pluto transiting the UK's 1066 chart Sun not only put the conjunction in a different sign (Sagittarius rather than Capricorn), but also significantly changed the actual timing. To compensate for nearly a thousand years of accrued precession, Sidereal Pluto reached the UK's Sun seven years later than by Tropical reckoning. So rather than 2012, the sidereal Pluto-Sun conjunction arrived in 2019, coinciding with the UK making its historic break with Europe. 

Sidereal Solar Returns come into their own even more since they are not affected by precession. By aged six, Tropical solar returns are already two hours 'fast', which is enough to give different angles to a horoscope. For this reason the Western Sidereal school of astrology pays great attention to the technique of Solar and Lunar returns.

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