Zodiac zero points: equinox and Lahiri reference
The foundational comparison between an equinox-anchored tropical longitude and a Lahiri-sidereal longitude derived from the same celestial state.
Frame comparison · released 2026-08-18
Shared fact substrate
The body, instant, observer assumptions, and underlying ecliptic direction are unchanged. The comparison begins from one retained tropical longitude rather than calculating two unrelated skies.
Required shared inputs
- One UTC instant
- One ephemeris state
- One ecliptic reference frame
- One numerical precision policy
- Named Lahiri ayanāṁśa and version
Tropical view
Longitude is measured from the true equinox of date. Zero Aries follows the equinoctial origin, so seasonal sign labels remain tied to that moving reference.
Lahiri-sidereal view
The declared Lahiri offset is subtracted and the result normalized to 0–360 degrees. Zero Aries follows that named sidereal convention, not every possible stellar zodiac.
Where they agree
Both views describe the same time-indexed celestial direction and preserve the same body identity, motion state, and ephemeris provenance.
Where they disagree
They assign different longitude numbers, sign labels, and degrees within sign because their zero points differ. Neither label can be silently substituted for the other.
Preservation policy
Store the tropical longitude, named ayanāṁśa, numerical offset, and resulting sidereal longitude as separate fields in one provenance bundle.
Prohibited synthesis
Do not average the longitudes, call Lahiri “the sidereal zodiac,” or select a zero point after reading an interpretation or outcome.
What empirical comparison requires
Treat tropical and sidereal outputs as separate candidate models. Any performance claim requires preregistered features, outcomes, horizons, baselines, model-selection policy, multiplicity control, and prospective scoring that retains misses and abstentions.
Method sources
These sources define calculation and namespace policy. They do not determine which astrology system is true.
- Celestial fact-layer specification
Maha Celestial
The shared instant, observer, ephemeris, reference-frame, precision, software, and provenance fields from which both chart frames are derived.
Boundary: Reproducible celestial geometry does not validate an astrological interpretation.
- Lahiri ayanāṁśa calculations
Maha Celestial
Maha’s declared transformation from retained tropical longitude to a separate Lahiri-sidereal longitude.
Boundary: Selecting Lahiri defines one sidereal convention; it does not establish that sidereal astrology is superior or empirically valid.
- Tropical versus sidereal astrology
Maha Celestial
The policy that tropical and sidereal charts remain parallel declared models with separate feature and rule namespaces.
Boundary: The guide is a methodology declaration, not an adjudication between traditions.