All the ayanamshas: who created them, when and why

Forty-seven ayanamshas is not seventy-three ways of solving one problem. It is seventy-three different answers to the question "count from where", and each answer rests on its own reference point. Here is what those points are and who chose them.

The principle

The zodiac can be anchored to the sky in two ways. The tropical zodiac is counted from the vernal equinox — a moving point, so the tropical zodiac is tied to the seasons and 0° Aries always coincides with the start of astrological spring. The sidereal one is anchored to the fixed stars.

Precession creates the gap between them: the Earth's axis slowly traces a circle in about 26,000 years, carrying the equinox with it. Over that time the zodiac shifts by roughly 50 arcseconds a year, or a degree every 72 years. The two and a half dozen degrees accumulated over two thousand years is a whole sign.

An ayanamsha is the angle to subtract to convert tropical coordinates into sidereal ones. Its size depends on which fixed point was chosen as zero. That choice can be made in many ways: a star, a pair of stars, the direction of the galactic centre, the plane of an equator, a text with tables. Each choice yields its own value, and all of them are "correct" within their own tradition.

This is the key point: the difference between ayanamshas is not a calculation error but a difference of convention. Choosing the scale matters more than the scale's precision.

The Vedic scales

This is the Indian tradition, from which the sidereal systems descend in their present form. In India the ayanamsha is not an astrological detail but part of official astronomy: festivals, calendar months and planetary positions for panchangas are all computed from it.

Lahiri (Chitra Paksha) is the main scale of Indian astronomy, adopted as official and made the basis of Indian calendars. It is named for the astronomer Surya Siddhanta, whose tables it reproduces: Lahiri recomputed the Sun's motion along the sidereal zodiac and derived a reckoning consistent with the texts. This is not an arbitrary anchor but the result of fitting an observed curve to a source. It is what almost all modern Vedic calculations assume, and it is the default here. Its value is about 23.85° for 2000.

Lahiri (1940) is a variant of the same scale recomputed for a different reference epoch. The difference from modern Lahiri is negligible, but mid-20th century this was a separate practice and it still turns up in older tables.

Lahiri (VP285) is the variant obtained from a publication by Venkata Pattabhirama Vridha Lakshminatha Shastri (VP), number 285. The anchor is the same as in classical Lahiri, but the figure is derived from one specific edition of the ephemerides. Useful when you need to reproduce that exact computation.

Lahiri (ICRC) is the variant reconciled with the ICRC ephemerides — that is, with the processing of solar and lunar positions the International Celestial Reference Coordinate system treats as authoritative. It differs from the classical value by a fraction of a degree.

Krishnamurti is the ayanamsha proposed by the astronomer and astrologer S. Krishnamurti. It is an attempt to build a scale from observations of the modern era rather than from an Indian text. Hence a noticeable divergence from Lahiri: about 23.7° against 23.85° for 2000, roughly two tenths of a degree. For most people that is immaterial, but at a sign boundary it gives a different result.

Krishnamurti (VP291) is the same idea, derived from a different VP edition, number 291. In the VP list these are adjacent numbers, and the difference between 285 and 291 shows how much the result depends on which dataset was used.

Raman is the scale proposed by the astronomer B. V. Raman. It differs noticeably from the Indian ones: about 22.4° for 2000, nearly a degree and a half below Lahiri. The Moon in the sidereal zodiac by Raman is shifted relative to the Indian reckoning and the signs differ visibly. Raman worked in the Vedic framework but relied on his own computations rather than the Indian tables.

Ushashashi is a scale attributed to the astronomer Ushashashi. It belongs to the same group of Indian "observational" variants: it agrees with the Indian tradition in method but has its own offset value, so at the margins the signs do not match Lahiri.

Djwhal Khul descends from the work of the modern Indian astronomer Djwal Koul. It is one of the later attempts to obtain the value from observation rather than from a text. It sits in the same group as Ushashashi: Indian framework, own anchor.

Yukteshwar is the scale associated with the name of Sanyan Yukteshwar. Among the earliest Indian "new" scales to depart from the classical one, with a value around 22.5° for 2000 — noticeably below Indian Lahiri.

J. N. Bhasin is the scale of the astronomer Janakiram Narayan Bhasin. Another Indian attempt to compute the ayanamsha independently. It belongs to the group where the spread reaches a degree and a half, which is to say there is no agreed base value within the Indian tradition itself.

De Luce is attributed to the modern researcher De Luce and published as a "reconstructed" value obtained by comparing historical sources. It stands apart, because it is an attempt to recover retroactively what was used at a particular historical moment rather than to measure today's value.

The Western scales

Fagan/Bradley is the main scale of Western sidereal astrology. It was used by R. Bradley in the early 20th century, and before him by the astronomer-researcher V. Fagan. Its value is about 24.0°, roughly 0.2° greater than Indian Lahiri. That matters: if you are reading a Western source it is almost certainly Fagan/Bradley, and its signs will differ from the Indian ones by about one sign for part of the population.

Aldebaran (15 Tau) has an exotic anchor: instead of the classical reference point it uses a specific catalogue position for the star Aldebaran. This is a rare case of an ayanamsha tied to one star through a modern catalogue rather than an ancient text. Useful as a cross-check against observations.

The Babylonian and ancient scales

Babylonian astrology is the older branch, from which Greek practice and the whole Western numbering of signs later grew. Its way of fixing the zodiac does not match the Indian one, so its ayanamshas differ.

Hipparchus is the ancient Greek scale going back to the 2nd century BC astronomer. It is an early attempt to express precession in coordinates: Hipparchus compared stellar positions with records of earlier observations and estimated the shift. What matters is that he posed the same problem as the Indians but two and a half centuries earlier than the European tradition solved it systematically.

Sassanian is the scale of the Sasanian Persian period, 3rd–7th century. Persian astronomers systematised the Babylonian and Indian inheritance, including the zodiac reference. This ayanamsha reconstructs what was accepted in Islamic Iran before Indian tables displaced the local schools.

Valens Moon is associated with the tradition attributed to Vettius Valens, the author of the Anthologies. Whether that text belongs to him, and what exactly it recorded, remains a matter of debate among historians of astronomy; hence the conditional name.

Babylonian (Kugler 1, 2 and 3) are three variants from the work of Otto Kugler, who reconstructed the Babylonian system from cuneiform tablets. The number denotes different readings or different datings of the source texts: Kugler found that some Babylonian tables agree with each other while others give a different value. It turned out these are different epochs of observation rather than errors, and three variants are more honest than one averaged figure.

Babylonian (Huber) is the reconstruction following the work of Paul Huber, who worked specifically on dating Babylonian observations. It differs from the Kugler variants because it rests on a stricter chronology.

Babylonian (ETPSC) is the variant descending from the Early Science programme at the University of Edinburgh — a canonicalised Babylonian value in modern historiographic treatment.

Babylonian (Britton) follows the work of Stephen Britton, a specialist in the history of ancient astronomy. It belongs to the same group as Huber's but with a different dating of the original observations.

The Indian textual scales

These are not observational values but a reproduction of what is written in the classical Sanskrit texts. The difference between them is a difference between texts, not between observations.

Surya Siddhanta is anchored on the text of the same name, regarded as the oldest surviving astronomical treatise of the Sanskrit tradition. The scale reproduces the solar motion described there.

Surya Siddhanta (mean Sun) is the variant that takes as its reference not the Sun's own motion along the ecliptic but its mean position. The difference is that the real Sun moves unevenly along the ecliptic, and you may either follow the true position or the mean one. These are two conventions inside a single text.

Aryabhata is anchored on the Aryabhatiya. The principle is the same as in the Surya Siddhanta but with a different model of motion and different tables. Aryabhata lived in the 6th century and his system differs noticeably from the later Vedic one.

Aryabhata (mean Sun) is the same "mean Sun" variant as above, applied to Aryabhata's model.

Aryabhata (522 CE) ties the figure to a dating of the text from which the reconstructions start. The point is that knowledge accumulated gradually, and later redactions may treat that date as current.

SS Revati — "SS" denotes the Indian standard, and Revati is one of the nakshatras, the lunar mansions or limiting points of the ecliptic that served as an anchor in the Indian tradition. This scale is tied to that point.

SS Chitra is the variant anchored on Chitra, the second nakshatra. The reference point differs from Revati's, so the offset value will differ too.

True Chitra means the Sun's motion is followed along the true rather than the mean ecliptic — that is, the inclination of the ecliptic to the orbital plane is taken into account. For subtleties like this the list keeps separate entries.

True Revati is the same qualification applied to the Revati anchor.

True Pushya uses the third nakshatra, Pushya, with the true-ecliptic correction.

True Mula uses Mula, the fourth nakshatra. Mula is the point where, in the Indian tradition, the ecliptic and the celestial equator intersect.

True Sheoran is the variant associated with a modern reconstruction of the Indian zodiacal system that adds a correction for the angle between the ecliptic and the plane of Earth's orbit. This is no longer a classical scale but a modern attempt to bring the Indian system in line with the current precession model.

The star-based and galactic scales

A separate and perhaps the most unexpected group. Here the zero of the zodiac is tied not to a star or a text but to the structure of the Galaxy itself — to its centre or to the plane of its equator. The logic is appealing: if you want the most "stellar" reference point possible, take the largest and most distant object available.

Galactic centre 0° Sagittarius ties the zero to the direction of the galactic centre, which in the tropical system falls at roughly 0° Sagittarius — hence the name. It acts on two figures at once: the difference from Lahiri reaches three and a half degrees.

Galactic centre (R. Gilbrand) is the variant computed by R. Gilbrand. It differs because it used different source data on the position of the centre, so the value is different even though the idea is the same.

Galactic centre Mula (Wilhelm) is Wilhelm's calculation, resting on the centre's position in the Mula system. The subtlety is that here not only the anchor but the reference point changes.

Galactic centre (Cochrane) is an independent reconstruction by Cochrane. Three independent computations of one and the same direction give three close but non-identical values — an object lesson in how fine a quantity this is.

Galactic equator (IAU 1958) puts the zero not on the centre but on the plane of the galactic equator in the 1958 standard definition. This is a completely different convention: a plane rather than a point.

Galactic equator (true) distinguishes the true inclination of the galactic plane from the mean one. The difference is on the order of tenths of a degree.

Galactic equator (Mula) is the equator, but in the Indian reference system.

Galactic equator (Fiorenza) is Fiorenza's calculation. The same idea as the IAU version, but with a different choice of source coordinates.

Galactic alignment (Mardyks) is the most unusual of all: here the zero is chosen so that the galactic and ecliptic equators are aligned — that is, the solution is sought from the condition that two planes coincide. This is a construction whose anchor is not an object at all but a relation between two planes.

The epochs

The three entries above are not ayanamshas in the strict sense but reference epochs. The difference between them lies not in tradition but in which year is taken as the origin when longitudes are computed.

J2000 is the epoch 2000 January 1.0, the standard reference position. It is the norm for modern catalogues: all coordinates are reduced to that moment and motion between epochs is handled separately.

J1900 is the same for the beginning of the 20th century. It still appears in older ephemerides and observations.

B1950 is epoch 1950.0 in the FK4 frame rather than the Julian one. The difference between B1950 and J1950 is about two tenths of a degree, arising from differences in how the frame itself is defined. That is precisely why two standards cannot be mixed directly.

Comparative table

All forty-seven entries are gathered below by what actually distinguishes them: the reference point, the tradition, and the period. Numeric values are deliberately omitted — they depend on the year you are computing for and on how the true ecliptic is treated, so the things to compare are the principles, not the numbers.

How to choose

If you have never thought about this, take Lahiri: it is the main scale of Indian astronomy, calendars are built on it, and it is what most modern sidereal calculations assume. If you come from Western astrology you will find Fagan/Bradley more familiar — but do not be surprised when Indian sources give you a different sign.

What is not worth doing is comparing systems without saying which ayanamsha was used. Numbers with no scale attached almost always lead to the false conclusion that one source is wrong.

And it is worth keeping in mind this: the difference between scales is a difference of convention, not of accuracy. All of them describe the same physical phenomenon, just from different reference points.