There are at least 40 house systems for astrologers to choose from. Although how the house systems are derived can be complex there are basically two classifications: Quadrant/Equal division, and Lunes/Semi-arc.
Quadrant/Equal Division System
Quadrant/Equal Division systems take a circle—either the equator, ecliptic, or prime vertical— and divide it equally into four quadrants.
The 1st quarter is the ascendant to the IC (10th cusp).
The 2nd quarter is the IC to the descendant (7th cusp).
The 3rd quarter is the descendant to the MC (4th cusp).
The 4th quarter is the MC to the Ascendant.
Various methods subdivide each quadrant into three smaller sections to arrive at 12 houses.
These houses are divided by either a space system, measuring physical distance, or at time system measuring how long it takes to travel the distance of the chosen circle using Sidereal time.
In this classification, is the Equal House system which simplifies matters by dividing one of the great circles, most commonly the ecliptic, into 12 equal arcs of 30° each.
Lunes/Semi-arc Systems
Lunes/Semi-arc systems divide a sphere into 12 equal lunes. Lunes are crescent-shaped sections created when a sphere is divided by two intersecting planes—sort of like the sections of an orange. In this category are some of the most commonly used house systems and some you’ve probably never heard of:
In the Equal Lunes systems there are:
- Ascendant Equal House
- Meridian Equal House—also called Axial, Equatorial, and Zariel
- Campanus
- Horizontal House
- In the Unequal Lunes systems there are:
- Regiomontanus
- Morinus
- In the Semi-arc House systems there are:
- Placidus
- Pseudo-Placidus
- Koch—also called Birthplace system
- Then there is a Miscellaneous subcategory here that includes:
- Topocentric
- Porphyry
- Natural Graduation
What System is Best?
This is really an unanswerable question. Different astrologers will favor one house system over another making it a matter of preference rather than of correctness. However, certain house systems are better suited for certain types of charts than others, especially when casting charts for locations close to the poles.
What an astrologer intends to do with astrology may determine which house system is best to use. In forecasting work, for example, Placidus is preferred by many astrologers. Cosmobiologists often prefer the Koch system.
In History
In history, politics have played a part in what house system astrologers used. From the 16th through the 18th centuries in England and France whether an astrologer used Regiomontanus or Placidus was determined by whether they were a Protestant (Regiomontanus) or Catholic (Placidus). Placidus was a Catholic monk and what house system an astrologer was loyal to made social statement.
There is no widespread agreement about which house system works best. Below are brief descriptions of the most commonly used systems.
Albategnian
Introduced in the 10th century by Arabian astrologer Prince Muhammad ben Gebir al Batani, this system divides the prime vertical into diurnal and nocturnal arcs that are then subdivided into equal parts by two declination circles. This is thought to have been the foundation for the Placidean system.
Alcabitian (Alcabitius)
This is the oldest known house system. It was devised by astrologer Alcabitius in the first century AD (although some think it was really 12th century Arabian astrologer Alchabitus who invented it).
This system works much like the Koch system using trisection of semi-arcs by time division. Alcabitian divides the diurnal circle (the small circle parallel to the equator, passing through the ascendant) of the ascendant into twelve arcs.
The portion of this diurnal circle that lies in each quadrant is trisected to obtain the houses. The diurnal and nocturnal arcs are then divided by two declination circles. This produces unequal semi-arcs. This is considered a good system for any charts calculated near the polar regions because there will always be an ascendant.
Aries
This system always places 0° Aries on the ascendant and 0° Capricorn at the MC. the rest of the cusps are at 0° of their respective signs.
Campanus
This system, adapted from an earlier Arabian system was devised in the 13th century by either astrologer/mathematician Giovanni Campano, or Johannes Campanus. No one is sure which was the original author. This is the house system favored by Sidereal astrologers.
Campanus houses are calculated by dividing the prime vertical (the great circle that passes through the east point of the horizon) into 30° arcs beginning at the Eastern horizon.
These divisions are then projected onto the ecliptic by drawing circles from the north the south point of the horizon. Where these north-south lines intersect the ecliptic are the Campanus house cusps.
Houses near the horizon are often larger and can cause more planets to be placed in the 12th and 1st houses than would be the case with other house systems.
Many astrologers hold that cusps should mark the center of the house instead of its boundaries, as in the Campanus system.
This system doesn’t work well for charts calculated for the polar regions.
Equal
The Equal house systems go back to the 1st century BC. However, this particular system is accredited to 19th-century Australian astrologer Zariel. It is also called the Zariel Division system or the Ascendant Equal House system.
The Equal House system should not be confused with an equal house chart where all cusps are equally spaced such as the Aries system uses.
To obtain the cusps, divide the ecliptic into twelve arcs of 30° each. Then project these points on to the circles that meet at the north and south poles of the ecliptic.
Usually, but not always, the ascendant is the 1st cusp and the 10th house cusp is the Zenith’s longitude (nonagesimal).
This system works well with charts calculated for the polar regions.
Koch
Koch is a variation of the Alcabitius system. Although made popular by German astrologer Walter Koch in 1962, it was really invented by two other Germans named Specht and Zanziger.
Koch’s system is also known as the Birthplace system and the GOH system from the German “Geburtsortes Hausertabellen.”
In the Koch system, the diurnal semi-arc is trisected by time division. This produces a grid that can’t be used in the polar regions—something the Alcabitian system could.
To create a Koch chart, trisect the MC semi-arcs from the ascendant to the Midheaven, and from the IC to the ascendant. Then project these trisected points on to the ecliptic with ascension (altitude) circles paralleling the horizon.
Koch has some unique features—some useful, some not. Because of the odd way the houses are derived, the 10th house can sometimes be on the horizon. And, the 10th house cusp on the ecliptic is the MC, but the 10th house curve off the ecliptic doesn’t align with the meridian circle.
This causes other houses cusps to not be clearly defined from the ecliptic. This is a little hard to picture, but simply put, the Koch House system can sometimes produce some improbable results.
Cosmobiologists often prefer the Koch system because they believe that house cusps on the ecliptic are too sensitive to ecliptic transits, directions, and progressions.
Another big problem with the Koch system is that it can only be used up to 60° latitude.
Meridian
In the early 1900’s, David Cope, whose pen name was Zariel, devised the Meridian house system. This is a favorite of Uranian astrologers.
To calculate a Meridian system chart, divide the celestial equator into twelve 30° arcs. Then project these onto the ecliptic with hour circles (circles that pass through the north and south celestial poles).
Where these lines intersect the ecliptic are the Meridian house cusps. This produces houses that are exactly two sidereal hours long and places the MC as the cusp of the 10th house.
The difference between this and the Equal House System is that the divisions from the MC instead of from the ascendant.
Morinus
Although named after 17th-century astrologer Jean Morin de Villefranche, he didn’t invent it. In fact, he used the Regiomontanus system. No one really knows who invented this system.
To calculate Morinus, divide the celestial equator into twelve equal 30° sections starting with 0° Aries. Then draw lines from the north to the south pole of the ecliptic through these 12 points on the celestial equator.
The places where the longitude lines intersect the ecliptic are the Morinus house cusps.
The MC and the ASC, determined by the intersection of the Lunes with the ecliptic, are not always the 10th and 1st house cusps.
The problem with the Morinus system is that none of the conventional house cusps always apply. However, it can be used for the polar regions.
Placidus
Named after 17th-century monk Placidus de Tito, no one really knows who invented it, although some historians think it was 8th-century Arabian astrologer, ben Djabir.
Placidus, also called the semi-arc system, is a time system. The house cusps are derived by the time taken to cover a certain space. The time, in right ascension, is taken for each degree of the ecliptic to rise on its own parallel of declination.
This is measured from the IC to the ascendant (nocturnal semi-arc) and from the ascendant to the MC (diurnal semi-arc).
The house cusps are 1/3 and 2/3 points of these semi-arcs. This produces lines that resemble sine waves.
This is not a good system to use for Polar regions and there are no ecliptic house cusps. Still, this is the most widely used house system today.
Porphyry
This system is also called the Sripathi. Named after Porphyry, a 3rd century AD astrologer.
To calculate a Porphyry chart, trisect the ecliptic angular distance between the Midheaven and the ascendant, and between the IC and the ascendant. This produces the 10th through the 3rd houses.
From the ascendant to the MC the houses are equal. The houses from the MC to the descendant are equal, but not the same as the houses from the ascendant to the MC.
The problem with Porphyry is that it produces different sizes of houses that can suddenly change without gradation as the angles are crossed and, the houses don’t reside entirely on either side of the horizon.
However, in Porphyry’s favor, cusps can be calculated at the polar regions even if they are unconventional.
Regiomontanus
Named after 15th-century astrologer Johannes Mulla (pen name Regiomontanus), this system uses trisection of a quadrant of the celestial equator by 30° arcs using house circles.
The cusp of the first house is the horizon and the degrees where the circles intersect the ecliptic are the other cusps.
This produces unequal houses that change progressively and gradually in size from house to house.
The ascendant is always the 1st house and the MC is always the 10th house. But the cusps are in the middle of the houses instead of at the boundaries.
Many astrologers say this system is useless for forecasting.
Solar
When a birth time is unknown, this system is the most commonly used.
The Sun’s position is set for the ascendant. The other cusps are assigned the same degrees and minutes for each successive sign.
This isn’t really a house system, but a type of equal house chart. It’s important not to confuse this with a Solar system, which places the position of the Sun on the 4th house cusp or the MC (used for mundane charts).
Topocentric
This is my favorite because it corrects the distortion effects of the Placidus cusps at high latitudes.
With Topocentric the polar axis is the fixed reference point. It measures house cusps by the rotation of the geocentric horizon around the axis.
The celestial equator is divided into twelve 30° arcs then these lines are projected onto the ecliptic. Ascension circles are used for latitudes above 60° or below -60°.
The major drawback to Topocentric is that it is so mathematically intricate, it is all but impossible to calculate by hand.
Other Systems
Uranian astrologers us specific systems that don’t include houses at all but rely on harmonics of planets. A good explanation of Uranian astrology can be found on http://theuranianastrologer.com/new-blog-2
For more detailed information about the house systems, look at Computers and Astrology, a Universal User’s Guide and Reference by Patricia Foreman, Good Earth Publications.