Zodiac sign boundary sensitivity
When a sign label should be marked unstable because model or input uncertainty overlaps a 30° boundary.
Calculation contract · released 2026-08-18
Definition
A sign is a floor-based classification of normalized longitude into twelve 30° intervals; the continuous longitude is the underlying calculated fact.
Calculation procedure
Measure angular distance to the nearest 30° boundary, combine relevant uncertainty envelopes, and flag or withhold the sign when the envelope crosses that boundary.
Required inputs
- Unrounded longitude
- Coordinate frame
- Combined angular uncertainty
- Boundary inclusion policy
Maha convention
Maha treats exact-boundary labels in the conformance corpus as non-normative and compares continuous geometry instead.
Uncertainty and edge cases
Rounding before classification can move 29°59′59.9″ to 0° of the next sign even when the stored value remains below the boundary.
What this does not establish
A stable sign classification does not make its interpretation empirically supported.
Authoritative references
These sources establish the calculation vocabulary, data product, or transformation convention. They do not establish astrological interpretation.
- Astronomy Engine
Don Cross (cosinekitty) · 2.1.19
Locally computed Sun and Moon positions derived from the VSOP87 and JPL-derived lunar theories, together with rise and set times, at the accuracy stated in the library documentation.
Boundary: Positions are computed in process rather than fetched from an authority, so a fact citing this source carries a digest over the computed values and not over a provider response body. Its accuracy is adequate for calendrical work and is not a substitute for a Horizons query where sub-arcsecond agreement matters.
- 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.