Placidus — Astrology glossary

Placidus is the most widely used house system in modern Western astrology. It divides the houses by time rather than space: it tracks how long a degree of the zodiac takes to travel from the horizon to the midheaven and splits that span into equal segments. This produces houses of unequal size, and the distortion grows at higher latitudes, where some houses become very large and others very small. The system matters because the house a planet falls into depends entirely on which method is used, so two astrologers reading the same birth data can place a planet in different houses simply by choosing different systems. For example, a Sun calculated near a house boundary under Placidus may sit in the 9th house, while a whole-sign chart places it in the 10th.