Porphyry House System

The Porphyry house system, attributed to the 3rd-century philosopher Porphyry of Tyre, uses a simple and elegant method: each quadrant between angular house cusps (Ascendant, MC, Descendant, IC) is divided into three equal arcs. This produces houses of varying size but avoids the extreme distortions that Placidus and other time-based systems can create at high latitudes. Porphyry is mathematically stable at all latitudes, making it a reliable fallback when Placidus calculations break down for the specific birth location and time.

If Placidus cannot produce usable cusps for your birth location and time, TriAstra uses Porphyry houses to give you stable house placements. The interpretation remains the same—only the mathematical method adapts to the chart.