Placidus Houses: Calculation Inputs and Polar Limitations
How Placidus houses are defined, which time and location inputs they require, and why high latitudes can cause failures. A reference, not a calculator.
Calculation contract · released 2026-08-18
Definition
Placidus is a time-proportional quadrant system whose intermediate cusps are derived from diurnal motion between angular positions.
Calculation procedure
Compute the ascendant and meridian angles in a declared frame, solve the Placidus semi-arc equations for intermediate cusps, and report any latitude-domain failure.
Required inputs
- Instant and observer coordinates
- Reference frame and sidereal time
- Polar failure policy
Maha convention
Maha does not currently use Placidus for Jyotiṣa production reports; this reference exists to make cross-software comparisons explicit.
Uncertainty and edge cases
Implementations can fail or substitute another system at extreme latitudes. Silent fallback makes two charts incomparable.
What this does not establish
Placidus and whole-sign charts must be evaluated as separate declared models, not averaged.
Authoritative references
These sources establish the calculation vocabulary, data product, or transformation convention. They do not establish astrological interpretation.
- 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.
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