HOUSE SYSTEMS USED IN ASTROLOGY
There are many house systems to choose from, but many have fallen by the wayside in recent years and are little used. For beginners the Equal House System is the most basic and simplest to understand. There are some astrologers who still use this system and it does have its validity. In fact it probably has more validity than the others do, as it is the oldest one, dating back some two thousand years and has its origins in the natural zodiac. Everyone has their favourite house system to use and some are very similar. Personally, I prefer to use both the Equal House System and Koch particularly for Horary astrology, though I do vary this at times.
The various House Systems are based on dividing time, as in Placidus or Koch, the ecliptic (Equal House) or space (Campanus). Probably the most common system in current use is Placidus, one of the quadrant systems, which uses the axis of the MC/IC as the cusps of the tenth/fourth houses. Some house systems, such as Placidus and all others listed here apart from the Equal House System, do not work well in higher latitudes as being too close to the pole some houses become huge, while others disappear altogether. They are all disposed to intercepted signs. The following is a list of the most common systems in current use, though there are many more.
Campanus - This system uses the four angles as the cusps of the 1st, 4th, 7th and 10th house and the division is linked to the four cardinal points. There appears to be some discrepancy regarding the pioneer of this system, although I accept that it may be due to the translation of the name. It is variously attributed to Johannes Campanus (Johannes being the latin version of John) or to Giovanni di Campani, both having lived in the 13th century. (perhaps someone with better knowledge than I would let me know)
Equal House - the simplest of all. This system uses the degree of the Ascendant as the basis for all the succeeding house cusps, so that each house begins at the same degree but of the next sign. It involves no further calculation of house cusps once the Ascendant is found as the houses are divided equally and there can be no intercepted houses. This is the basis for the natural zodiac so it would seem logical to follow it. The main disadvantage of using this system is that the MC/IC axis can be anywhere between the eighth/second house and the eleventh/fifth house. As the MC is a very important angle and is relative to the matters of the tenth house, it can be argued that the other systems which have the MC as the cusp of the tenth house, are more valid.
Koch - known as the birth place method, it uses time for its divisions counting from the MC to the Ascendant. This makes the birth place co-ordinates vital in the calculation. Because it uses the MC as its starting point, the MC is the most important angle of this type of chart and represents the ego, who you are and who you would like to become. In other words, the path of life starts with the MC and represents freedom of the individual and free will. It was devised by a German astrologer and advocated by Dr Walter Koch (1895-1970), hence its name.
Placidus - devised by Placidus de Tito, a 17th century mathematician. It is based on the time taken for the Ascendant to become the MC. As with the Koch system, it is open to having intercepted signs. Intercepted signs are those that do not form any house cusp but are sandwiched between two others within a house. This system gained popularity in the 19th century due to its use in Raphael's ephemeris since 1821.
Porphyry - Porphyry lived from approximately 233 - c.304 AD. He was a Greek philosopher known for his work on Ptolemy's "Tetrabiblos", the main foundation of astrology. The system is based on division of the ecliptic, it divides the houses by trisecting the semi-arc of the Ascendant/MC. The four angles are used respectively for the 1st, 4th, 7th and 10th houses, then each quadrant is divided equally as measured on the ecliptic. This system is not used as much as the others.
Regiomontanus - This system was more widely used in the old texts of astrology, but has for the most part fallen into disuse in recent years. It is based on the earth's movement around the sun, measured by the equator and the horizon. A 15th century astronomer, Johannes Muller, known as "Regiomontanus" devised the system.
Solar - often used where the time of birth is unknown. The position of the sun becomes the ascendant and the chart is read from there. This system is the one used in general daily sun-sign horoscopes.