Method comparison · independent chart frames
Tropical versus sidereal astrology
Tropical and sidereal charts can consume the same celestial facts while producing different zodiac labels. Maha treats them as parallel declared models, not ingredients in an unlabeled synthesis.
Published 2026-08-18
Calculation chain
One UTC instant and ephemeris → tropical longitude retained → named ayanāṁśa applied for a separate sidereal longitude.
What remains the same
The underlying instant, geographic input, planetary state, and ephemeris calculation are shared celestial facts. The Sun–Moon angle and physical planetary configuration do not change merely because a different zodiac label is applied.
What changes
Zodiac sign, degree within sign, sign-based houses, nakṣatra placement, and rules conditioned on those labels can change. House cusps can differ for additional reasons when traditions use different house systems. Each derived result therefore records its coordinate frame and method.
- Tropical: zero point follows the equinox
- Sidereal: zero point follows a named stellar-reference convention
- Lahiri: one specific sidereal ayanāṁśa, not a synonym for every sidereal chart
- Whole-sign and quadrant houses: separate choices from zodiac frame
How Maha compares the systems
The compiler preserves separate feature namespaces, rule packs, predictions, and scores. A tropical rule cannot consume a sidereal placement unless the rule explicitly declares that cross-system dependency. Historical calibration can compare both systems against the same outcome, but it must report model selection and multiple-testing controls.
Interpretive boundary
Agreement or disagreement between traditions is not a scientific validation result. Predictive performance must be measured prospectively for each declared model.