Ayanamsa (ayanāṃśa: from Sanskrit ayana 'movement' and aṃśa 'component'), alsoayanabhāga (from Sanskrit bhāga 'portion'), is theSanskrit term for many systems used inHindu astrology to account for theprecession of equinoxes.[1][verification needed] There are also systems of ayanamsa used inWestern sidereal astrology, such as the Fagan/Bradley Ayanamsa.[2]
There are various systems of Ayanamsa that are in use in Hindu astrology (also known asVedic astrology) such as theRaman Ayanamsa[3] and the Krishnamurthy Ayanamsa,[1] but the Lahiri Ayanamsa, named after itsinventor,astronomer Nirmal Chandra Lahiri (1906–1980), is by far the most prevalent system in India.[2][4] Critics of Lahiri Ayanamsa have proposed an ayanamsa called True Chitra Paksha Ayanamsa.[2][4] There are other existing ayanamsa such as Raman, Pushya Paksha, Rohini, Kërr A.I, Usha Shashi and Chandra Hari. However, Dulakara ayanamsa is precise; the zero ayanamsa year according to it is 232 CE. Indrasena ayanamsa is a variant of Dulakara by the same author and the same zero ayanamsa year (232 CE), but differs from it by the precessional rate, which is 50.03" per year.[5]
The use of ayanamsa to account for the precession of equinoxes is believed to have been defined inVedic texts[which?] at least 2,500 years before theGreek astronomerHipparchus quantified the precession of equinoxes in 127 B.C.[citation needed] While critical scholars believe these "Vedic texts", at least those centering Spica Cittā (or 0° Libra, Tūla Rāśi), were composed in the common era, between 200 and 400 CE.
Lahiri falsely [unsubstantiated claim] intended that Spica be centred in Cittā (0° Tūla, tropical LIB) and exactly 180° from tropical ARI. Spica's ecliptic longitude was approximately 203.2° in the mid 1950s, 203.84° in 2000 and thus its presumed ayanamsa is 23.84° (J2000), 24.2° by 2026, and 25.0° by 2083.
The actual longitude of Spica is closer to 29° Virgo[6] than 0° Libra. Thus, the Lahiri ayanamsa is nearly one degree less than the true value of ayanamsa.
Centring Spica in Cittā, as Lahiri does, pushes Aldebaran and Regulus off-centre and pushes Antares west and outside its namesake nakshatra. Allowing Spica 45' to 1° east of Cittā's center better aligns Pleiades in Kattikā, centers Aldebaran in Rohini, Regulus in Maghā, and Antares to define the western boundary of Jyestha.
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