← Encyclopedia of Astrology · lesson 78/235
House system
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What it is
The zodiac's twelve signs are fixed divisions of the Sun's path. The twelve houses are different: they divide the sky as seen from one place at one moment, starting from the horizon and the meridian, and they are what tells you in which area of life a planet operates. A house system is the rule for drawing those twelve divisions. There is no single agreed rule, and Bernadette Brady puts it plainly: there is no right or wrong system, and each gives a slightly different grid.
Why they differ
The sky is a sphere and the houses must be marked on the ecliptic, a tilted circle. Different systems divide different things — time, space, the ecliptic itself — and then project the result onto the ecliptic. The main families:
- Whole Sign. The rising sign is the whole first house, the next sign the second, and so on: each house is exactly one sign. It is the oldest method in the Hellenistic tradition, and the Ascendant falls somewhere inside the first house rather than on its cusp.
- Equal. Each house is thirty degrees, counted from the exact degree of the Ascendant. The Midheaven then floats and may fall in the ninth, tenth or eleventh house.
- Placidus. Divides the time each degree takes to travel from the horizon to the meridian into thirds. It is the most widely used modern system and the one this chart uses unless another is chosen.
- Koch. Similar in spirit to Placidus, built on the Midheaven's time of rising at the birthplace; it gives broadly similar houses.
- Regiomontanus and Campanus. Divide space rather than time — the celestial equator and the prime vertical respectively — into equal sections. Regiomontanus was the classic system of horary astrologers such as William Lilly.
- Porphyry. Simply trisects each quadrant between the angles.
In the quadrant systems (Placidus, Koch, Regiomontanus, Campanus, Porphyry) the four angles are the cusps of the first, fourth, seventh and tenth houses, and the houses vary in size. At high latitudes they can become very uneven, and a sign may be wholly contained inside a house (an intercepted sign); Placidus and Koch break down altogether near the polar circles, where Equal or Whole Sign still work.
What it changes
The planets' signs and aspects stay the same in every system. What can change is the house a planet falls in, especially when it sits near a cusp, and with it the area of life it is read through. The Ascendant and Midheaven do not change — only whether they mark house cusps.