Lahiri ayanāṁśa convention
Maha’s exact Lahiri conversion contract, independent validation envelope, and boundary behavior.
Calculation contract · released 2026-08-18
Definition
Lahiri ayanāṁśa is one named sidereal zero-point convention; it supplies the angular offset subtracted from tropical longitude.
Calculation procedure
Evaluate Maha’s J2000 Lahiri anchor at the instant using its declared precession polynomial, subtract from tropical longitude, normalize, and retain both values.
Required inputs
- UTC instant converted for the ephemeris path
- Tropical longitude of date
- Lahiri implementation version
Maha convention
The current implementation is anchored at J2000 and advanced using IAU 2006 general precession. Across the frozen 1600–2099 corpus it differs from Swiss SIDM_LAHIRI by at most 0.004123°.
Uncertainty and edge cases
That measured difference is an implementation envelope, not a claim that either zero point is physically privileged.
What this does not establish
Lahiri selection defines chart coordinates; it does not validate Jyotiṣa predictions.
Authoritative references
These sources establish the calculation vocabulary, data product, or transformation convention. They do not establish astrological interpretation.
- Standards of Fundamental Astronomy
International Astronomical Union SOFA Board · 2023-10-11
IAU-approved algorithms for astrometry, time scales, Earth rotation, precession, nutation, coordinate transformations, and related fundamental astronomy.
Boundary: SOFA supplies standard algorithms and validation programs; an implementation must still record its exact release and input data products.
- Swiss Ephemeris general documentation
Astrodienst AG · 2.10 documentation, checked 2026-08-18
An independent ephemeris implementation, supported reference choices, house calculations, and its dual-license boundary.
Boundary: Maha does not bundle or call Swiss Ephemeris in production. Frozen conformance results are validation evidence, not permission to redistribute its software or data.