Although there are a number of different house systems in use today, most of these systems use either the ascendant (ASC) or mid-heaven (MC) as a point of reference or house cusp division. The most significant differences between the many house systems are the sizes of the intermediate houses which are houses two and three, five and six, eight and nine, and eleven and twelve. The most frequently asked question is, “Which house system should I use?” It should be remembered that all house systems work, but some are more efficient than others in certain types of astrology. Ultimately, it doesn’t matter which house system you use providing it works for you.
EQUAL HOUSE SYSTEM
The Equal house system is the only system that is erected in the plane of the Earths orbit. It is reputed to be the earliest system of all and it dates back to the first century BC. It was recommended by Parasara and may have been used by Ptolemy. In this system, the zodiac is erected in the plane of the Earths orbit around the Sun which comprises of a 360 degree circle that surrounds the Earth. It uses the ascendant as the first house cusp, and then divides the zodiac into twelve equal houses of exactly thirty degrees starting from the sign and degree on the ascendant. The mid-heaven is often more, or less than ninety degrees (three signs) from the ascendant, therefore it is not often placed on the tenth house cusp, but marked where it appears in the mid-heaven according to the latitude and longitude of birth. The mid-heaven is taken as an important point; it is the point of self-mastery.
The Placidus system was popularised in the seventeenth century by the Italian Benedictine monk Placidus de Titis (1590-1668). Placidus did not invent the Placidus system, though it was found in his work “Primum Mobile”. Placidus tables were discovered before the birth of Placidus on an astrolabe in 1305, and Placidus tables were made available in 1604.
The Placidus system is based on the time it takes for each degree of the ecliptic to rise from the lower meridian to the ascendant and from the ascendant to the mid-heaven which is placed on the tenth house cusp. The four semi arcs, made by the movement of the ecliptic, are trisected to form the cusps of the twelve houses. This system works for latitudes near the equator because the houses become more equal in their number of degrees, but in the higher northern and southern latitudes an increasing amount of distortion occurs because the houses become intercepted, and as a consequence the Placidus system loses its accuracy.
I have experimented with many different house systems and I have come to the conclusion that there is not any one correct house system. Although I prefer to use the Equal house system, it may not be correct for everyone. If you are unsure as to which house system to use, then experiment with the many house systems available today and you will find the one that is correct for you.