Placidus

The Placidus house system is the most commonly used method for dividing a birth chart into 12 houses in Western astrology. Named after the 17th-century astrologer Placidus de Titis, it calculates house cusps based on the time it takes for a point on the ecliptic to travel from the Ascendant to the MC (Medium Coeli) and then to the Descendant. This results in unequal house sizes, with larger houses in some signs and smaller ones in others.

How it works

In a Placidus chart, the Ascendant (rising sign) marks the cusp of the 1st house, and the MC marks the cusp of the 10th house. The other house cusps are determined by dividing the time it takes for the ecliptic to move between these points into equal temporal segments. Because the Earth's rotation is not uniform relative to the ecliptic, houses can vary significantly in size, especially at extreme latitudes. For example, someone born near the Arctic Circle may have some houses spanning 40 degrees while others are only a few degrees wide. This system is considered "space-based" because it uses the local horizon and meridian as reference points.

In practice

When reading a Placidus chart, note that planets in intercepted houses (houses that fall entirely within a sign) may express their energy more subtly. The unequal house sizes can also emphasize certain life areas: a large 7th house might indicate a long period of relationship themes, while a small 4th house could suggest a more concentrated focus on home and family. Most astrologers find Placidus intuitive for interpreting daily life and psychological patterns. If you want to see your own Placidus chart, you can generate your natal chart here.