Sidereal zodiac longitude
Why “sidereal” is incomplete without a named zero-point convention and numerical ayanāṁśa.
Calculation contract · released 2026-08-18
Definition
Sidereal zodiac longitude is a tropical ecliptic longitude transformed by a selected stellar-reference offset called an ayanāṁśa.
Calculation procedure
Compute and retain tropical longitude, calculate the named ayanāṁśa for the same epoch, subtract it, and normalize the result to [0°, 360°).
Required inputs
- Tropical longitude
- Named ayanāṁśa method
- Epoch and precession model
- Normalization policy
Maha convention
Maha’s Jyotiṣa production path uses Lahiri (Chitrapakṣa); other sidereal systems must occupy separate named feature namespaces.
Uncertainty and edge cases
Different ayanāṁśas can change signs, nakṣatras, pādas, and whole-sign houses near boundaries.
What this does not establish
A sidereal conversion does not show that one astrological system is empirically superior.
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.