Ayanamsa
every reader
What the tradition reads
The ayanamsa is the angular distance between the tropical zodiac, which is fixed to the equinoxes, and the sidereal zodiac, which is fixed to the visible constellations, and it is the single number that lets a sidereal astrologer convert a tropical longitude into a sidereal one. Because the equinox itself creeps slowly backward against the fixed stars, a motion called precession, the ayanamsa is not a constant but grows year by year, roughly one degree every seventy two years, and every sidereal school must therefore commit to a zero point and a rate before its signs mean anything at all. Vedic astrology treats the ayanamsa as a plain correction rather than a matter of opinion, and the tradition holds the Lahiri ayanamsa, which fixes the star Spica near the first degree of sidereal Libra, as the default for Vedic calculation. N.C. Lahiri sat on the Calendar Reform Committee the Government of India convened under the astrophysicist Meghnad Saha in 1952, the body whose recommendations became India's 1957 national calendar, though the Raman and Krishnamurthy ayanamsas remain in use among smaller schools that argue for a different zero point or a different rate of precession. Western sidereal astrologers, a minority within Western practice, generally use the Fagan Bradley ayanamsa instead, a figure close to but not identical with Lahiri's.
The story
Ayanamsa is a Sanskrit compound of ayana, meaning movement or a course, and amsha, meaning a part or a portion, so the word names the precessional "moving part" by which the two zodiacs have drifted apart, rather than any zodiac sign itself. Some ayanamsa proponents trace the idea to calculations implied in older Vedic texts, but the sources that quantify it are generally dated well after the Hellenistic astronomer Hipparchus independently discovered and measured the precession of the equinoxes in the second century BCE. The two zodiacs coincided closely around two thousand years ago, when the vernal equinox point still stood near the first degree of Aries in both systems, and the whole of Western tropical astrology has kept that original alignment as its convention ever since, defining Aries as beginning at the equinox regardless of where the constellation itself has since drifted to. The ayanamsa is therefore best understood as the record of everything that has changed since that shared starting point: the Lahiri figure, named for N.C. Lahiri, a member of the Government of India's 1952 Calendar Reform Committee, stood near twenty three and a half degrees at the turn of this century and continues to grow.
Written from
Corpus key glossary:ayanamsa.