Ayanamsa

Ayanamsa or Ayanamsha is the Sanskrit term for the difference in degrees between the traditional sidereal zodiac, based on relatively fixed ecliptic stellar coordinates and the "tropical" one, familiar in the West, having its zero point based on the sun's apparent placement on the vernal equinox.

The ancient Mesopotamian observers referenced celestial events from approximately thirty-two "normal stars" located within a few degrees of the ecliptic, but Claudius Ptolemy seems to be one of the earliest to attempt mapping the stars on a coherent system of spherical coordinates, owing much to the efforts of predecessors. It is unclear whether Ptolemy actually invented the tropical zodiac by intention or through later misunderstanding of his contemporary observation that the sun appeared to enter Aries at about the time of the vernal equinox. Correcting for the measurement errors in Ptolemy's coordinates, a date around 53 CE provides a good fit for matching sidereal and tropical zodiacs, and on the whole, such a date matches reasonably well with current IAU boundaries of the zodiacal constellations, though the latter vary considerably from thirty-degree portions of the ecliptic.

There is a notion in ancient literature of all the seven visible luminaries returning to a starting point at the culmination of cycles, and in fact, on 8 March 53 CE (JD=1740483.68) this DID occur, with the sun, moon, and five visible planets converging within a 25-degree span in Pisces and Aquarius. Actually, similar convergences are not so rare as one might think, occurring roughly eight times in a given millennium.

It is difficult to precisely determine the boundaries of the sidereal zodiac used in the ancient world, because degree positions were not cited until the later dates, and often these were inconsistent, apparently interpolated from tables rather than direct observations. The astrological consensus holds that the tropical and sidereal zodiacs matched up sometime in the third century CE. Fagan & Bradley suggested the year 221, while Lahiri, making an official determination for the government of India, favored 285. Several dates in the fourth century are advocated by other Indian astrologers, citing a better match between actual star positions and the lunar mansions named for them.

Close convergences of the seven luminaries also occurred on the dates 7 April 232, 11 June 294, and 6 October 332. For the epoch 2000.0, these would give respective ayanamsa values of 24.597, 23.735, and 23.204 degrees. Interesting to consider also that on August 15, 312 CE, a much rarer sort of celestial event occurred. The seven luminaries returned effectively to their own domiciles, all within a span of 180 degrees, from Cancer to Capricorn. This seems a unique event in a long span of millennia. We are hedging a bit on Mars, only, which has technically passed into the zero degree of Sagittarius, unless considered as 30 Scorpio. Still, it is exceptional, though unknown whether astrologers in 312 CE remarked on it. This is a few weeks before Constantine met Licinius on the famed Milvian Bridge, so the time is a sensitive pivot of European history. This date would yield a 2000.0 ayanamsa of 23.483 degrees. It happens to make better sense than most values in mapping the Vimsottari dasas in my own chart, though I always reserve a good dose of skepticism anyway.

By the way, the fixed stars are not equally "fixed" and most of the candidates for "fiducial" star have enough proper motion to have shifted a bit since classical times. Spica has longitudinally shifted more than an arc-minute in that span of time. Not much, perhaps, but there are several potential "fiducials" that are far less "shifty". Among the Babylonian normal stars, Zeta Tauri, Rho Leonis, or Beta Scorpii are rather better, though none are conveniently located on a sign boundary. The 312 CE date does give us a fiducial star directly on the border of Cancer and Leo, namely Psi Leonis, just 13 arc-minutes from the ecliptic. The point between Cancer and Leo has been cited as "the birthplace of the sun" and a line to its opposite degree, near Delta Capricorni, bisects the zodiac into the diurnal and nocturnal rulership zones. Interesting!

Useful links on the star lore of antiquity:

Constellations of Words

The Lost Zodiac of the Stars

Ptolemy's Almagest

Robert Hand: Historical Astrological Texts

Muladhara Rahu Sikhi Chakra

Renaissance Astrology

Star Coordinate Data

Astrodienst

Egyptian Sky Charts

Yeats & the Lunar Mansions

The Constellations & Their Stars

Recommended references:

Allen, Richard H.,Star Names, Their Lore and Meaning, 1889, Dover Publications 1963.(ISBN 0-486-21079-0).

Robson, Vivian E.,The Fixed Stars and Constellations in Astrology, 1923, Ascella Publications, UK,(ISBN: 1-898503-50-8).

last updated: 21 Sep 2008, by:

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