Ayanamsa (ayanāṃsa , from ayana "movement" and aṃsa "component") is the Sanskrit term for the longitudinal difference between the Tropical (Sayana) and Sidereal (Nirayana) zodiacs.[1]
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Overview
The ayanamsa is defined as the angle by which the sidereal ecliptic longitude of a celestial body is less than its tropical ecliptic longitude. The ayanamsa is mostly assumed to be close to be 24° today, according to N. C. Lahiri 23.85° as of 2000. This value would correspond to a coincidence of the sidereal with the tropical zodiac in or near the year 293 AD, roughly compatible with the assumption that the tradition of the tropical zodiac as current in Western astrology was fixed by Ptolemy in the 3rd century.
- The sidereal ecliptic longitude of a celestial body is its longitude on the ecliptic defined with respect to the "fixed" stars.
- The tropical ecliptic longitude of a celestial body is its longitude on the ecliptic defined with respect to the vernal equinox point.
Since the vernal equinox point precesses westwards at a rate of about 50".29 per year (the rate has been accelerating) with respect to the fixed stars, the longitude of a fixed body defined with respect to it will increase slowly. On the other hand, since the stars "do not move" (this ignores the effect of proper motion) the longitude of a fixed body defined with respect to them will never change.
Traditional Vedic astrology (Jyotisha) uses a system of sidereal longitude. When the practitioners of these schools of astrology use modern astronomical calculations to determine the position of celestial bodies, they need to take into account the difference caused by the different reference point used in specifying the longitude, and this they call the ayanamsa.
But all orthodox schools of Vedic astrology reject modern astronomy and still base their computations upon traditional texts and treatises, mostly following the Surya Siddhanta or treatises based on it. They use ayanāmsa according to Surya Siddhānta, in which ayanāmsa rises from 0° to +27° during 1800 years, then decreases to 0° and further to -27°, thereafter rising again, thus oscillating within a rage of ±27° instead of cyclically moving in a circle as modern concept of ayanāmsa suggests.
Manjula advocated a cyclical concept of ayanāmsa, but it could not gain currency among almanac makers. In West Theon (ca. 4th century AD) was the earliest known advocate of Surya Siddhāntic type of ayanāmsa (although Theon said trepidation varied within a rage of ±8° only : Surya Siddhāntic trepidation was deduced by multiplying 90° with 0.3, Theon multiplied 27° again with 0.3 to get 8° ). This oscillating type of ayanāmsa, known as trepidation, was a favourite of Indian, Arab and European astrologers and astronomers till the time of Copernicus. Modern science does not support the idea of trepidation or oscillating ayanāmsa. 499 AD is regarded as the zero date of this type of ayanāmsa according to Surya Siddhānta, Aryabhatiya and other ancient treatises. Thus the present value of traditional ayanāmsa is nearly +22.64°, which is less than modern the value of about +24°.
After 2299 AD, the traditional ayanāmsa will start decreasing from the maximum value of +27°, while modern value will keep on increasing. Equations of sunrise and ascendant (lagna) need accurate value of ayanāmsa, upon which all important components of religious almanac and horoscopes are based in India.
The ayanamsha describes the increasing gap between the tropical and sidereal zodiacs. The ayanamsa, changes continually through the Precession of the Equinoxes at the rate of approximately 50" a year, is currently about 24°.
Western Astrologers Fagan and Bradley computed it at 24 degrees in 1950; however, there are various values in use in India. While the general consensus is that the star Alcyon represents the first point of Aries, differences arise because of the indefinite ancient boundaries of the constellation of Aries.
See also
References
- ^ The Essentials of Vedic Astrology, by Komilla Sutton, The Wessex Astrologer Ltd., Bournemouth, England.
External links
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