House Systems: Placidus, Whole Sign, Equal, and Porphyry: A Source-Reviewed Guide
A planet at 28 degrees of a rising sign may be first house in whole-sign but twelfth in Placidus. Scope and limits are explicit.
Overview
Each house system has a named geometric or sign-based rule; the chart records system code, twelve cusps, angle relations, fallback behavior, and changed placements. The page shows exactly what to verify, how to repeat the method, where a plausible near miss fails, which variants change the result, and what the evidence cannot establish.
At a glance
- Direct scope
- Reviewed finding — Whole-sign, equal, Porphyry, and Placidus houses partition the chart by different rules: sign boundaries, fixed thirty-degree arcs, quadrant trisection, or semi-arc timing. They need not assign one planet to the same house.
- Evidence to verify
- Method checkpoint — Calculate verified angles first, select one named system and version, generate all twelve cusps at full precision, test ordering and opposition invariants, classify boundary planets by an explicit half-open interval, and retain alternatives.
- Repeatable method
- Worked-case result — A planet at 28 degrees of a rising sign may be first house in whole-sign but twelfth in Placidus. The comparison keeps identical birth data and changes only the house algorithm.
- Worked example
- Failure condition — Displaying a house number without the system makes a calculator difference look like corrupted planetary data. Planet longitude may agree perfectly while only cusp construction changes.
- Near miss
- Documented variant — Some traditions use whole-sign houses with quadrant angles as sensitive points; equal houses may begin at the exact Ascendant or at a sign boundary in variant usage. The implementation must name its rule.
- Limits and safety
- Use boundary — No house system has universal empirical authority. System choice should remain visible, polar failure must not be hidden, and interpretation should never present a changed house assignment as a changed person.
Definition and Scope
Each house system has a named geometric or sign-based rule; the chart records system code, twelve cusps, angle relations, fallback behavior, and changed placements.
Whole-sign, equal, Porphyry, and Placidus houses partition the chart by different rules: sign boundaries, fixed thirty-degree arcs, quadrant trisection, or semi-arc timing. They need not assign one planet to the same house.
Evidence and Repeatable Method
Calculate verified angles first, select one named system and version, generate all twelve cusps at full precision, test ordering and opposition invariants, classify boundary planets by an explicit half-open interval, and retain alternatives.
Worked Example and Near Miss
A planet at 28 degrees of a rising sign may be first house in whole-sign but twelfth in Placidus. The comparison keeps identical birth data and changes only the house algorithm.
Displaying a house number without the system makes a calculator difference look like corrupted planetary data. Planet longitude may agree perfectly while only cusp construction changes.
Variants and Disagreement
Some traditions use whole-sign houses with quadrant angles as sensitive points; equal houses may begin at the exact Ascendant or at a sign boundary in variant usage. The implementation must name its rule.
Limits and Safe Use
No house system has universal empirical authority. System choice should remain visible, polar failure must not be hidden, and interpretation should never present a changed house assignment as a changed person.
Sources and editorial basis
- Swiss Ephemeris 2.10 DocumentationSwiss Ephemeris 2.10 manual, chapters 2 “The Ephemerides”, 6 “Sidereal Time, Ascendant, MC, Houses, Vertex”, and 7 “Delta T”, pages 5–64Public technical documentation for ephemerides, time conversions, sidereal time, apparent positions, houses, nodes, and Delta T; software policy and version must still be disclosed.
- NCGR-PAA Level II CurriculumNCGR-PAA Level II Curriculum PDF, Part 1 “Astronomy and Chart Calculations” and Part 2 “Delineation and Synthesis”, sections 1–9A professional astrology curriculum covering astronomy, chart calculation, house systems, dignity, rulership, transits, progressions, and synthesis; it records practice standards rather than empirical proof.