Almost everybody has heard of natal astrology. That’s the branch of astrology that gives information about the nature and course of a person’s life based on the relationship of various astrological symbols in the heavens at the time they were born. While natal astrology looks at your entire life, horary astrology answers a specific question. You don’t need to know the time of your birth or what your rising sign is, all you need is a sincere burning desire to have the answer to your question!
This 6-minute video explains what a horary reading is, and how to pose a horary question.
In this post I am going to contrast the Alcabitius semi-arc system of house division with the Placidus house system.
Both Alcabitius and Placidus are time-based house systems, as opposed to Porphyry, which is purely an ecliptic-based system.
In Porphyry, we start at the point of the ascendant (the point where the horizon meets the ecliptic) and measure the number of degrees along the ecliptic to the MC (the point where the ecliptic meets the local meridian). We trisect that into three equal houses and in this way get the cusp positions for the tenth, eleventh and twelfth houses, and by extension for the fourth, fifth and sixth houses. Easy!
Then we measure the number of degrees from the MC to the descendant and trisect THAT! That will give us the house cups for the seventh, eighth and ninth houses, and by extension the first, second and third houses. Note that in the chart above, houses 7, 8 and 9 are smaller than houses 10, 11 and 12.
To a certain extent, using the local meridian in Porphyry takes into account the latitude of the native in that unless one was born on the equator, the distance from the horizon to the midheaven (MC) will not be the same as from the MC to the descendant.
Let’s contrast Porphyry with how the Alcabitius house system is calculated:
In Alcabitius, instead of simply trisecting the ecliptic between the ascendant point and the MC, we trisect the amount of time the Sun takes to rise along the ecliptic from the ascendant to the MC.
So for example, in Paris today the Sun rose over the horizon at 7h33m13s and reached its culmination at the MC at 13h54m26s. So, we subtract the time of the Ascendant from that of the MC and find that it took 6 hours 21 minutes and 13s for the Sun to travel from the ascendant to the MC.
Here is the chart of the Sun rising on 1st April 2021 over Paris:
Using the Alcabitius system, we simply divide the total time by three to get the eleventh and twelfth house cusps. 6h21m13s divided by 3 = 2h 7m 4.33s. We take the quotient of the division (2h7m4.33s) and add it to the time of the ascendant (7h33m13s). By doing this, we learn that the Sun was at the cusp of the 12th house at 9:40:17.33s.
To get the time the Sun arrived at the 11th house cusp, we simply add 2h7m4.33s to the time of the 12th house cusp, which would be at 11:47:21.65s
Then, with the help of basic high school trigonometry, we determine what degrees on the ecliptic the Sun would have been on at the times we just calculated, and we have our house cusps!
Here is a chart of the Sun culminating over Paris. Because of the latitude, the culmination point is not directly above our head, but slightly to the west. Because of this, notice that houses 7, 8 and 9 are smaller in ecliptic degrees than houses 12, 11 and 10:
And now, we finally arrive at the Placidus house system!
Placidus is very similar to Alcabitius, but it takes Alcabitius a step further.
By trisecting or dividing the ecliptic in three equal parts from the ascendant to the MC (and then again from the MC to the descendant), Alcabitius is not taking into account that the twelve signs of the zodiac do not necessarily have the same ascension times as they pass over the ascendant: Depending on the native’s latitude, some signs take long to pass over the ascendant than others!
Straight versus crooked signs:
As we saw in the last blog, because of the earth’s tilt in relation to the ecliptic, in the northern hemisphere Cancer, Leo, Virgo, Libra, Scorpio and Sagittarius take longer to pass over the ascendant than the other six signs, and are called “signs of long ascension” or “straight signs” or “signs of right ascension”. The other six signs are Capricorn, Aquarius, Pisces, Aries, Taurus and Gemini, and are called signs of “short ascension”, or “crooked signs. Because of the earth’s tilt, the crooked signs actually appear to be flatter or “stooped” than the other signs, and as a result, they go by faster as they pass by the horizon due to the earth’s daily rotation.
In the southern hemisphere, the perspective is reversed, so what is a “long sign” in the northern hemisphere becomes a “short sign” in the southern hemisphere!
Going back to the northern hemisphere now: Even with the six “long ascension” signs, the ascension times are not uniform. The duration of the ascension time very much depends on what latitude the native is placed on. So a native born in Chicago at 11am will have a different set of ascension times than a native born in Houston, which is further south and obviously at a different latitude.
So the beauty of Placidus is that it takes into account of the latitude of the native when determining the ascension time each sign takes to go over the horizon at the time of birth.
As with Alcabitius, we measure the time it takes for the Sun to go from the Ascendant and MC and divide the total by three. Let’s say the quotient of this division is 2 hours 33 minutes 15 seconds.
And then we go a step further in Placidus:
We physically measure where the Sun will be in its rotation on the ecliptic 2h33m15s after it was at the point of the ascendant. Where the Sun will be on the ecliptic depends entirely what latitude the native is on using Placidus, for as we have seen, some astrological signs take longer for the Sun to pass through than others, even though they all have the same longitudinal width of 30° on the ecliptic!
If we have a long ascension sign like Libra on the horizon, the sizes of the houses will look quite different than if we have a sign of short ascension on the horizon, such as Aquarius.
Here are two chart cast for the same place and time using Alcabitius and Placidus. Have a look to compare the difference:
Note that the Sun took longer to move (in a diurnal direction) through Placidus than it did through Albitius. In Alcabitius, the Sun arrived at the twelfth house cusp at 20° Leo 03′. In Placidus, the Sun arrived seven degrees earlier, at 27° Leo 44.
The reason for the discrepancy is because in Alcabitius we are simply trisecting the distance between the Ascendant and the MC. Each of the three houses have the same number of degrees. In Placidus, the length of time it takes for the Sun to pass through each of the signs is taken into consideration, hence the differences when we compare the cusps.
To conclude, both Alcabitius and Placidus are timed-based house systems, with Placidus being more concerned with the native’s latitude than Alcabitius and is thus more sensitive to the native’s location. In this way it is more geocentric or earth-based.
Speaking of earth-based house systems, it would be difficult to imagine a celestial circle that is more earth-based than the celestial equator, which is simply the earth’s equator projected out to the celestial sphere.
There are a number of house systems that are based on the longitudinal degrees of the equator, rather than the ecliptic. Perhaps the best known of them is the Regiomantanus house system. This was the system used by William Lilly. We’ll be taking a look at how Regiomontanus is calculated in the next installment.
In the first time-based house system that we looked at, the Alcabitius system, we carefully measured the time it took for the point of the ascendant (the point where the horizon meets the Sun’s path along the meridian), to reach the culmination point of the Sun at the midheaven, or MC (Medium Coeli).
We then took the total time of the Sun’s path along the ecliptic from the ascendant to the MC and divide the time it took into three equal parts. Adding one of these parts to the time of the ascendant gives us the time when the point of the ascendant reaches the 12th house cusp, adding the sum again gives us the 11th house cusp, and we convert those times into degree points on the ecliptic.
The beauty of this system is that it is linked to the local meridian, and thus more directly to the location of the earth-based native of the chart.
With Alcabitius, at first glance it would appear that since time is trisected between the ascendant and the MC, that the time it takes for the Sun (or any planet) to travel would be the same for each of the trisected houses, since each of the houses represent an equal amount of time.
However, this is not the case. And this is where the innovation of the Placidus system enters the picture.
The fact of the matter is that the Sun transverses some astrological signs more quickly than others. This is what William Lilly referred to as “straight signs” versus “crooked signs”. Or put another way, “signs of right ascension” as opposed to “signs of oblique ascension”, or “signs of long ascension” vs “signs of short ascension”.
Because of the way the earth is tilted with respect to the ecliptic, six of the constellations along the ecliptic seem flatter/not as tall/crooked/shorter than the other six, which appear to be standing upright, “straight”, or long.
The Sun takes less time with the crooked/oblique/short signs to “ascend” along the ecliptic than it does with the upright, straight, or long ones.
In the northern hemisphere, the signs of right ascension (straight/upright/long) are: Cancer, Leo, Virgo, Libra, Scorpio and Sagittarius.
The signs of oblique ascension (crooked/oblique/short) are: Capricorn, Aquarius, Pisces, Aries, Taurus, Gemini.
In the southern hemisphere, due to the earth’s tilt of 23.5° in relation to the ecliptic, these are reversed: i.e. the signs of long ascension become the signs of short ascension.
You can easily see for yourself how widely the ascension times vary for each sign in any astrological program capable of animating a chart wheel, such as Astro Gold or Solar Fire. I’ve prepared a demonstration video in Solar Fire to demonstrate this, you can do it yourself at home!
And here is a lovely YouTube video using Stellarium and Sumer 1.3 by Rumen Kolev which demonstrates the phenomenon of long ascension versus short ascension quite nicely, observe especially the image on the right:
So in summary, Porphyry is an ecliptic-based system which simply divides the ecliptic in three equal parts from the ascendant to the MC, and then again from the MC to the Descendant, and by extension to the rest of the 12 astrological houses.
Alcabitius is a time-based system, which measures the time it takes for the point of the ecliptic to move in a diurnal (primary, literally “to the right”) direction until it reaches the MC. We then divide the time by three (rather than dividing the ecliptic itself). Then we do this operation again from the IC to the ascendant, and by extension the rest of the twelve astrological houses.
Placidus was an innovation, in that it took into account that although the signs are a standardized 30° each on the ecliptic, the Sun moves along these signs at different rates of speed due to their positioning in relation to the local meridian. It is thus a more accurate representation of the size of an astrological house in relation to the native’s position on earth. We do not get this in any of the other previously mentioned house systems.
We will go more deeply into the Placidus system in the next post.
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.