HOUSE SYSTEMS
Porphyry
Porphyry trisects each ecliptic arc between the Ascendant, Midheaven, Descendant and lower meridian.
The idea in context
Each zodiacal arc between successive primary angles is divided into three equal portions to form the intermediate house cusps.
MAKE IT CONCRETE
An example to picture
An angular quadrant spanning 96° is divided into three 32° houses; a neighboring 84° quadrant is divided into three 28° houses.
How to read it
Locate the four angles first, then follow the two intermediate cusps dividing each arc into thirds.
A common misunderstanding
Porphyry divides ecliptic arcs, not equal portions of clock time. Its houses need not be 30° each.
BRING IT BACK TO YOUR LIFE
A question to sit with
Which angle anchors the life area you are exploring, and how does its surrounding quadrant frame that reading?
Go deeper: the full reference
How to read it
The four quadrants can span different numbers of degrees, so the twelve houses need not be equal in size even though each quadrant is trisected.
Input and calculation limits
Porphyry still depends on calculated angles and a reliable birth time. A valid result is not a substitute for uncertain input data.
Compare one choice at a time
Changing the house system changes cusps and may change house assignments. It does not move the planets through the zodiac. These are interpretive frameworks, not measured personality traits or predictions. Private chart settings do not change dating compatibility.
Try reading your own birth chart
Create a free birth chart, select the placement or symbol you are learning about, and read it alongside this lesson. A planet’s sign, house and aspects add context; keep your recorded birth time and chart settings in view.
Connect the ideas
Placidus
A time-based quadrant system that divides the diurnal and nocturnal motion used to define intermediate house cusps. The Ascendant and Midheaven anchor the 1st and 10th cusps.
2 min readWhole Sign
The entire zodiac sign containing the Ascendant is the 1st House. Each following sign forms the next house, with cusps at sign boundaries.
2 min readEqual House
The exact Ascendant degree begins the 1st House, followed by eleven equal 30° sectors along the zodiac.
2 min readKoch
A time-based quadrant system using the birthplace latitude and the diurnal arc associated with the Midheaven to construct intermediate cusps.
2 min read