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 create at high latitudes. Porphyry is mathematically stable at all latitudes, making it a reliable alternative when Placidus calculations break down above 66 degrees.

If you were born at a high latitude, TriAstra uses Porphyry houses to give you accurate house placements. The interpretation remains the same—only the mathematical method adapts to your location.