What is Sidereal Astrology?

Updated: a day ago

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 Astrology actually is.

Short version

The Sidereal Zodiac is measured from prominent fixed stars of the ecliptic constellations rather than the Vernal Equinox. It is a fundamentally different concept to the Tropical zodiac, though the 12 equal 30° signs are interpreted in the same way. The original Sidereal zodiac remains fixed in space, while the Vernal 0° Aries drifts apart from the stars by a movement called 'precession of the Equinoxes'. Today the two zodiacs are separated by a distance (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 Babylonian (pre-Hellenistic) astrology in the West which underwent a major 20th Century revival. Sidereal astrologers use this zodiac for its vivid sign archetypes and more accurate, precession-free timing for transits and returns.

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Longer version

The Earth's axial wobble creates 'precession of the Equinoxes', a retrograde movement of the Vernal Point against the backdrop of the fixed stars, 1° degree every 72 years. In the 3rd century AD, the Sidereal and Tropical zodiacs overlapped when the moving Vernal Equinox came to a point in its 25,800 year cycle (known as The Great Year) where it aligned with the Sidereal fixed stars. For a short time the two zodiacs were one, and precisely at this time, the Hellenistic scholar Claudius Ptolemy wrote an influential  text, the Tetrabiblos, which defined the 0° Aries Point that commences the zodiac with the Spring Equinox. This was true for his time, though crucially, not for all times.

Ptolemy justified his theory 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 does not apply in the Southern Hemisphere where the seasons are reversed. Still, it is often said, 'Sidereal is based on the Stars, Tropical is based on the Seasons'.

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.

Crucially, even after Ptolemy's work inaugurated the new 'Tropical Zodiac', astrologers continued to use the original Sidereal sign meanings, elements, qualities and symbolism. The stars were treated as if they were moving rather than the Equinoxes, and instead of stellar divination it had the effect of making astrology itself earthbound. Precession was forgotten and Western astrologers carried on as if the year was forever 275 AD. This historical disruption continues up to the present time, where the two zodiacs 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.


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. There are 12 signs by definition of every culture that has ever used the zodiac: Babylonian, Egyptian, Persian, Greek, Roman, Indian. Astrologers have always known the constellation Ophiuchus cuts into the ecliptic plane, and integrated its Serpent-Bearer symbolism into the zodiacal sign of Scorpio.

Yes but the 'fixed stars' are also moving.

The average 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 is often confused with the fixed stars position, so that the royal star Regulus, for example, was assumed to have 'moved into Virgo' in the early 21st Century, even though this is a Tropical illusion. Sidereal Regulus stays where it is, and remains 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.

Yes, but the constellations aren't really equal:

A constellation is not a sign, which by definition 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.

Is Sidereal your past life?


But Tropical signs clearly work.

Does anyone ever question their tropical zodiac signs, on first sight? Hardly ever. 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.

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.

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.

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.


© 2014-20 by Adam Smith, all rights reserved

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