We’ve discussed ecliptic-based house systems such as whole sign houses, equal houses and Porphyry. Now I’d like to move on to two of the “time-based” house systems: Alcabitius and Placidus.
Ecliptic systems divide the ecliptic itself into houses. In the whole sign house system (WSH), the astrological sign itself becomes the house, with each sign/house consisting of a standardized 30° of ecliptical longitude. The Ascendant is floating freely within the first house, and the midheaven (M.C.) is generally floating anywhere between the 8th – eleventh houses.
Ditto for equal houses, except each house starts with the degree of the ascendant.
The Porphyry house system takes the distance from the Ascendant to the midheaven, and trisects it into three equal divisions, which determines the house cusp degrees for houses 10, 11 and 12, and by extension for houses 4, 5 and 6. Then, the longitudinal distance between the midheaven and the descendant is measured and trisected, giving us the degrees of houses 9, 8 and 7, and by extension the degrees for houses 3, 2 and 1. The Porphyry system is the simplest form of “quadrant house system”, so called because it divides the 360° circle of the ecliptic into four quadrants.
Now we come to the Alcabitius system of house division, which is called a “time-based” house system.
So how is Alcabitius time-based? What does this mean?
Consider the ascendant, the astrological point to the East where the horizon meets the ecliptic… This is the point where the Sun rises.
As the earth rotates this point will rise along the diurnal arc (i.e. the ecliptic) until it becomes the midheaven (MC), the point where the Sun culminates (not to be confused with the zenith).
The “time” we are speaking of here is the time it takes for the point of the ascendant to move along the “semi-arc” of the until it reaches the MC, the cusp of the tenth house, where it transverses the local meridian
This amount of time is then trisected in Alcabitius: it is divided into three equal parts, which we refer to as “trisecting the semi-arc of the ascendant”.
Thus, we are trisecting time in the Alcabitius system, as opposed to a system that is dividing solely the ecliptic, such as WSH, equal houses or Porphyry, and all that this implies symbolically (which we shall discuss in more depth a bit later on).
Back to Alcabitius now…
So, let us say that it takes 5 hours, 32 minutes and 16 seconds for the point of the ascendant to rise in a diurnal direction (primary direction) to the midheaven.
All one does is divide that by three, which gives us 1 hour 50.7 minutes. To determine the 12th house cusp we simply find out what longitudinal degree the ascendant was on at 1 hour 50.7 minutes after the precise hour of the rising point. We double that to find the eleventh house cusp, and to check one’s work we simply multiply by three, and if our calculations were correct, we arrive at the same degree as the midheaven.
Easy, right? At least it is conceptually. It is a beautiful and elegant system which was used widely in Europe from around the 10th century up until the introduction of the Regiomontanus system in the late 15th century.
The second and third house cusps are found the same way as the eleventh and twelfth, except rather than moving forward in time, we look back to when the point of the ascendant was at the IC, determine what time this occurred, divide the time it took by three and follow the same procedure for the lower semi arc that we used for the upper one.
One advantage of the Alcabitius system is that there is little less distortion in the relative sizes of the houses. For example, in Placidus – another time-based house system – at the latitude of Paris we sometimes find a huge sixth and twelfth house. In the Alcabitius house system the houses tend to be more evenly distributed, as a general rule.
Indeed, we would probably be using Alcabitius widely today if it had been included in Raphael’s Ephemeris, which was the standard reference for astrologers during the 19th and well into the 20th century. But alas, it wasn’t; it was Placidus that was included, which goes a long way to explaining the current popularity of Placidus, for astrologers tend to use whatever house system their teachers used. Quite understandable, of course. Though perhaps unfortunate.
In our next discussion, we will look at the Placidus system of house division to see how it is calculated, and compare it with Alcabitius.