Types of House Systems Explained
Written for self-reference and posted for those trying to learn and practice astrology seriously. Refer to my blog bio for more.
The houses are one of the most important concepts in astrology. They represent major themes and areas of your life, the world you inhabit, and your character, and understanding them is crucial to accurate natal interpretations. They are determined by the native's birth time and location, but also by the house system used.
This post is to help you understand what a house system is, and the most important differences between them. A follow-up post explaining my personal takes on when and how to use them is on the way. This one is solely for technical reference.
You'll notice below that the introduction includes a list of essential vocabulary. This is for reference. It is not necessary for seasoned astrologers to read. Feel free to skip ahead to the guide itself.
Newcomer's Glossary of Terms
The houses are a section of the natal chart in which objects and signs may fall. They are madly dividing the chart into twelve, and are named for their numerical order. So, the first house precedes the second house, the second house precedes the third house, etc.
A placement is a position in the chart. These positions are marked by degrees. There are 360º comprising the entire chart, obviously, but a placement is more often referred to by the degree out of 30º they occupy in the relevant zodiac sign. Placement may also refer more generally to the house or sign a specific position lands in.
Objects are any planets, non-planets such as asteroids and stars, or hypothetical planets which have placements. One may also use astronomical or other mathematical equations to determine significant positions of the chart. Such non-object placements are referred to as points.
Cusps are a type of point that marks the border between two houses. One house's territory begins with that house's cusp, and ends with that of the next house. So, the 1st house cusp marks the 1st house's beginning, but it also marks the 12th house's end. The 12th house cusp marks the 12th house's beginning but also the 11th house's end, and the 11th house cusp marks the 11th house's beginning and the 10th house's end, and so on, and so on.
The angles are the four most important cusps or points of a chart. They are generally found by referencing natal time and place. The four angles include the Ascendant (also referred to as the Rising), the Descendant, the Medium Coeli (also referred to as the Midheaven), and the Imum Coeli.
The Ascendant generally cusps or determines the sign of the first house. The Descendant is the angle opposite the Ascendant. It cusps or determines the sign of the seventh house. The Medium Coeli is the highest point of the chart. It either cusps the tenth house or, to my knowledge, exists somewhere between the 9th, 10th, and 11th house. The Imum Coeli is the angle standing opposite the Medium Coeli. It either cusps the fourth house or exists somewhere between the 3rd, 4th, and 5th house.
The Types of House Systems
There are three major types of house systems: temporal, spacial and ecliptic. The difference between them is in how they are calculated as well as the type of system it produces.
To call a system temporal means that it refers to the movement of celestial objects to determine house cusps.
To call it spacial means that the system refers to location in physical space to determine house cusps.
To call a system ecliptic means the houses are assigned equal divisions of 30º, with the Ascendant or Midheaven sometimes determining cusps, otherwise determining the houses' signs.
Placidus is the most popular temporal system. It is also the most commonly used system in Western astrology. It is a temporal and quadrant system. Quadrant systems prioritize calculating the angles, and calculate other cusps in relation to them.
Placidus is based on the arcs of heavenly objects. Basically: all objects have a set arc they travel through space. We divide that arc into twelve parts, making two halves of six parts each. The half exposed in the day is called the diurnal arc, and the half exposed at night is called the nocturnal arc.
The point between the two halves is represented by the Ascendant. (Hence the other name, the Rising, as this is the point from which objects rise out of the nocturnal arc and into the diurnal arc.) From this, the other four points can be calculated, such as the Descendant, which marks where objects transition from day to night, and the Midheaven, the highest point of the day's arc.
The Koch system is probably the second most popular temporal system, and is a relatively popular system for Western astrologers overall. It is also both a temporal and quadrant system.
The difference between Koch and Placidus is that while Placidus prioritizes calculating the Ascendant axis, Koch prioritizes calculating the Midheaven.
Campanus is the most popular spacial house system, and the only one I've personally seen used with any regularity. It is a spacial and quadrant system that references the birth location.
Campanus is similar to the previous systems in that it does rely on creating day and night halves of six parts each. However, rather than referencing the projected arc of objects, this system is created by dividing the celestial space itself.
The horizons divide the two halves, represented by the Ascendant, the western horizon where the sun rises, and the Descendant, the eastern horizon where it sets. The zenith, or the midpoint point of the sky during the day, Is marked by the Medium Coeli, and the nadir, or midpoint of the night sky, by the Imum Coeli.
Regiomantus is an alternative spacial and quadrant system that references the equator rather than the birth location.
At the start, I specified three major types of systems. This is true, but not the whole truth.
The Meridian system is calculated using both space and time, so technically, it counts as a spacial and temporal system. It is also a quadrant system, like those mentioned prior.
The Meridian system divides the celestial space into the halves of six, just like the spacial Campanus system, but the axis of this division is aligned to the celestial poles rather than on the horizon.
The Equal Sign system and the Whole Sign system are the two most popular ecliptic systems.
The Whole Sign system is the one I've see most used in Vedic. It assigns each house a 30º space which aligns with the occupied sign. Hence, a Taurus-ruled 1st house would have its cusp at 0º Taurus, regardless of the specific degree of the Ascendant.
The Equal Sign system begins by assigning a 30º space to the 1st house, starting with the Ascendant as its cusp, then assigns each preceding house a space of equal degrees. So, if the Ascendant is in 19º Taurus, the 2nd house cusp will be at 19º Gemini, the 3rd house cusp at 19º Cancer, and so on.
An alternative variation on the Equal Sign system is used by some, which prioritizes the Midheaven as the inciting cusp. This can result in Ascendants that do not land in the 1st house. So, say the native with a 19º Taurus Ascendant has their Midheaven at 7º Pisces. Using the Equal Sign MC system, the 10th house starts at 7º Pisces, the 11th starts at 7º Aries, the 12th at 7º Taurus, and the 1st at 7º Gemini, resulting in a 12th house placement for the Ascendant.
Of course, using the normal Equal Sign system on a chart with these placements would result in an 11th house Midheaven. This is the trade off of using an ecliptic system. It may seem strange or counterintuitive to quadrant system users, but it also opens up new avenues for placement interpretation.
Hoping this serves as a helpful reference. I will add a link to a second part containing an explanation of my own interpretations and suggestions for using each house system later. Thanks for reading, feel free to message, reply, and ask ♡♡♡♡
