The system used to divide the zodiac into twelve further segments called houses (see diagram). The houses form the horoscope's "terrestrial" frame of reference, as opposed to the zodiac which forms the "celestial" frame of reference.
There are both so-called equal and unequal house systems. However, no matter which system is used, the axes Ascendant/ Descendant and Medium Coeli/ Imum Coeli stay the same. In most cases, the Ascendant marks the cusp of the first house and the Medium Coeli the cusp of the tenth house.
Equal House Systems
Here the zodiac is divided into equal segments of thirty degrees with the Ascendant either marking the cusp of the first house or situated within it. The Medium Coeli, on the other hand, does not have to be in the tenth house but can be situated anywhere between the eighth and the eleventh house. Intercepted signs do not occur in equal house systems. The Whole Sign house system is the most ancient house system of all. There, the sign of the Ascendant is the first house, with the Ascendant somewhere in it.
Unequal House Systems
In the unequal house systems the four quadrants, i.e. the four segments defined by the main axes, are divided into three further segments of unequal size. However, the houses situated opposite each other are always the same size. There are numerous unequal house systems. The most well-known are:
This system is now rarely used. It originates from the 3rd century BCE and divides the four quadrants in three equal segments. The Porphyry system is based on the ecliptic.
This system was developed by Giovanni Campani (1233-1296). In the Campanus house system, the Prime Vertical (the great circle which takes in the East and West points on the horizon and runs from the zenith to the nadir) is divided by twelve. These divisions are then projected onto the ecliptic along great circles which meet at the North and South points on the horizon. The house cusps are situated at the points where the twelve circles cross the ecliptic.
In this system, developed by the mathematician, astronomer and astrologer Regiomontanus (Johannes Müller, 1436-1476), the celestial sphere is divided into twelve equal segments of thirty degrees. These divisions are projected onto the ecliptic along great circles that take in the North and South points on the horizon. The house positions are marked by the points at which the great circles cross the celestial sphere.
The Italian priest Placidus de Titis (1603-1668) developed a temporal system which trisects the distance between the Ascendant and both the Imum and Medium Coeli. The basis of measurement is the time taken for each degree of the ecliptic to rise from the nadir (Imum Coeli) to the Ascendant, and from the Ascendant to the Midheaven (Medium Coeli).
The Placidus House System is the most commonly used.
GOH or Koch
The so-called GOH system was propagated by the school principle Walter Koch (1895-1970) and is sometimes called the Koch House System. The circle of latitude at the place of birth is divided into equal segments.
There is no general agreement among astrologers as to which house system is the "correct one". No system has been proven to be inherently superior to the others. All that can be done is to choose a house system based on the personal experience of which one appears to give the most accurate results. The disadvantage of the unequal house systems is that they don't work for places at very high latitudes.
- Wikipedia: House (astrology)#Systems_of_house_division
- Overview: Available house systems in the Extended Chart Selection (Frequently asked questions; Astrodienst)
- Condensed presentation of the different house systems (by Paul, in a thread at Skyscript, 2016)
- Compare Your Birth Chart in Multiple House Systems (Astrology Library, 2020)
- Astronomy of Houses (Graham Bates, Urania Trust 2014)
- An Astrological House Formulary (Michael Munkasey; scribd)
- Astronomical Foundations of the Astrological Houses (Christopher Weidner; Astrodienst)
- The Natal Houses - What Do They Represent? (Dane Rudhyar, 1949)
- Also about Rudhyar's use of the Campanus system
- The Problems of House Division (Deborah Houlding, ca. 2006)
- The Polar Horoscope (Michael Wackford 2001/ 2007; Skyscript)
- Astrology in polar regions and on the southern hemisphere (Dieter Koch; Astrodienst)
- Whole Sign Houses, Quadrant Houses, and Equal Houses: Three Different Models for Astrology (Video David Cochrane, 2014)
- The Ascendant and Birth Charts near the Arctic Circle (Video Cochrane, 2014)
- An Astrological Dilemma: Polar Latitudes (Alova, 2009)
Notes and References
- Starting with the Ascendant (which usually is on the left)