Astrological Houses and Angles – 1:
Great Circles, House Classifications, House Division

– written by Philip Graves
– revised Sep 7, 2004
– reformatted for WordPress, June 4th, 2016


What is a figure or map?

In astrological tradition, figures or maps (later to be known more colloquially as ‘charts’) are circular diagrams showing the astronomical conditions at a particular time and place on earth. They offer a combined, integrated representation of the positions of astronomical factors affecting the earth as a whole at that time, measured along the plane of the celestial ecliptic by signs and degrees longitude of the zodiac (in western astrology, usually the tropical zodiac), and the projected position within the ecliptic of the space around a particular location on the Earth’s surface.

The simplest type of figure is a nativity, geniture or birth chart, which represents the astronomical conditions at the precise time and place of the birth of an individual.


Great Circles and Points

‘Great Circles’ are imaginary circular planes running through the centre of the Earth along naturally significant lines. The intersections of the ecliptic with the other Great Circles are called points, and are accorded influences by astrologers.

The Celestial Equator is an extension of the Earth’s equator into space.

The Celestial Ecliptic is the plane through which the Sun and planets apparently revolve around the Earth, and consists of a circle of 360º longitude at a slight incline to the equator, subdivided into the twelve signs of the zodiac of 30º each. Where the ecliptic intersects the Celestial Equator in the east (northwards) is called the Vernal Point or Aries Point.

The Horizon is a circle running through the centre of the Earth on a plane parallel to that of the visible horizon at any specified point on its surface. Where the ecliptic meets the Horizon in the east is called the Ascendant (ASC or AC) or rising degree; and in the west the Descendant (DESC or DC) or setting degree.

The Meridian is the circle running through the northern and southern horizons and the points directly overhead (the Zenith) and underneath (the Nadir) at the location concerned. Where it intersects the ecliptic above the horizon (in the south, in the Northern hemisphere) is the Midheaven or Medium Coeli (‘MC‘); and below the horizon (in the north, in the Northern hemisphere), exactly opposite the MC, the Lower Midheaven or Imum Coeli (‘IC‘). The ecliptic reaches its highest elevation above the horizon at the MC and its lowest descent below it at the IC.

At higher latitudes, the separation along the ecliptic of the Ascendant from the MC increases for longitudes of the MC from 0º Capricorn to 0º Cancer, but declines for longitudes of the MC from 0º Cancer to 0º Capricorn.

The Prime Vertical is the circle completed through the eastern and western horizons and the Zenith and Nadir. Where it intersects the ecliptic to the east is called the Anti-Vertex, and to the west is called the Vertex.

The Unnamed Great Circle runs through the eastern and western horizons and the North and South poles of the Earth. Where it intersects the ecliptic to the east is called the East Point or Equatorial Ascendant, and to the west is called the West Point.


What is a horoscope?

The horoscope (this term deriving from the Greek horoskopos meaning ‘marker of the hour’, originally referring strictly to the Ascendant) is a representation of the space around the locality of a birth or other event at its exact time, after projection onto the celestial ecliptic.

This space is divided into four quadrants connecting the four cardinal points or angles (the AC, IC, DC and MC) at the location and time concerned.

Each quadrant is divided into three houses, the first of which (corresponding to the cardinal constitution) is called an ‘angular house’; the second (fixed) a ‘succedent house’; and the third (mutable) a ‘cadent house’. The angles and houses so derived variably coincide with the signs and degrees of the tropical zodiac at different times of the same day in the same place, since they pass through all 360º of the zodiac in the 24 hours of the Earth’s rotation. A figure thus shows the positions of the celestial bodies in relation to both the tropical zodiac and the horoscope angles.

Movement from the ascendant sign and degree through each house in ascending order traces a forward path through the signs and degrees of the tropical zodiac. Yet this path is represented in anticlockwise motion by the figure, which also by tradition depicts the eastern horizon on its far left and the western horizon on its far right.

The first quadrant (houses 1, 2 and 3) extends from the AC in the east (left) to the IC (below); the second (houses 4, 5 and 6) from the IC to the DC in the west (right); the third (houses 7, 8 and 9) from the DC to the MC (top); and the fourth (houses 10, 11 and 12 from the MC to the AC, completing the circle.


Rising, culmination, and setting

During the course of a day, since the figure is always drawn with the horizon fixed across its lateral diameter yet the horizon and every house passes forward through the signs of the zodiac at an average rate of one sign per two hours, it appears that the zodiac revolves clockwise through the figure at the same rate, and that each sign in turn rises at the ascendant, culminates at the the Midheaven, and sets at the descendant before passing below the horizon again.

The same applies to the celestial bodies, although since they are themselves moving relative to the zodiac they will revolve clockwise slightly slower than the zodiac signs within the figure unless they are in retrograde motion.

The time taken for any sign of the zodiac to rise through the ascendant is called its ascension time. As a result of the inclination of the polar axis of the Earth in relation to the ecliptic, some signs rise faster than others; and this difference varies with latitude and the time of year, being most extreme at latitudes close to the north pole. The signs of long ascension (slower to rise) are Cancer, Leo, Virgo, Libra, Scorpio and Sagittarius. The signs of short ascension (faster rising) are Capricorn, Aquarius, Pisces, Aries, Taurus and Gemini. Yet every sign passes through the midheaven at a relatively even rate.


Classifications of the houses

The table below shows the four quadrants of the horoscope in relation to the angles where they begin, the houses of each modality they contain, and whether they are above or below the horizon and in the Eastern or Western hemisphere (from the perspective of the point on the earth’s surface being studied).

Angle entry  Horizon Hemisphere Houses Angular Succedent Cadent
Ascendant Below Eastern 1-3 1st 2nd 3rd
Immum Coeli Below Western 4-6 4th 5th 6th
Descendant Above Western 7-9 7th 8th 9th
Medium Coeli Above Eastern 10-12 10th 11th 12th

NB: In the table above, ‘Angle entry’ denotes ‘Angle of entry’

The houses can also be classified by element like the zodiac signs, but these groupings of houses have traditionally been given a separate set of names, as shown in the table below: the Fire houses are Individual or Life houses, the Earth houses are Temporal or Possessive houses, the Air houses are Relative or Association houses, and the Water houses are Terminal or Psychic houses.

Houses Individual Temporal Relative Terminal
1-4 1st 2nd 3rd 4th
5-8 5th 6th 7th 8th
9-12 9th 10th 11th 12th


A final astronomical classification of the houses, not to be confused with Western and Eastern as shown in the first table above, is into the Occidental houses, which are those in the two quadrants that extend anticlockwise from the horizon to the meridian, and Oriental ones, which are those in the two quadrants that extend anticlockwise from the meridian to the horizon.

Quadrant Entry point Exit point Classification Houses
1 Horizon(AC) Meridian (IC) Occidental 1,2,3
2 Meridian(IC) Horizon (DC) Oriental 4,5,6
3 Horizon (DC) Meridian (MC) Occidental 7,8,9
4 Meridian (MC) Horizon (AC) Oriental 10,11,12


House cusps

The divide connecting any house with the next is known as a ‘house cusp’, and its belonging is attributed to the next house. In other words, the cusp of a house is where that house begins. The cusps connecting the cadent and angular houses always correspond to the relevant physical cardinal point or angle at the locality and moment concerned, as described earlier (unless a house division method not referenced in all the angles, such as the Equal House system, is used, in which case, for example, the Midheaven (MC) may be located within the eighth or ninth house rather than on the cusp of the tenth).

However, the intermediary cusps: those connecting the angular and succedent houses, and the succedent and cadent houses: vary in their positions by sign and degree depending on the mathematical method or ‘house system’ used to divide up each quadrant before or after projecting the space around the location concerned onto the ecliptic (see below for more details).

The sign that falls on the cusp of each house is an important factor to interpret. The simplified diagram above shows the natural zodiac, whereby each house exactly coincides with the sign of the same number! In practice it is very rare for this to happen, but the natural zodiac helpfully illustrates the natural affinity between signs and corresponding houses.


Celestial bodies in the houses

The positions of the various planets, the Sun and Moon, and the Moon’s Nodes in the zodiac at each moment in time are calculated with great precision by astronomical laboratories and listed in an ephemeris by sign and degree and minute for the start or middle of each day every year Greenwich Mean Time. It is simple to interpolate from there, allowing for time zone correction, their exact positions at any time and in any location on earth.

Their positions in the houses will then be apparent from the relation of their sign and degree position to that of the cusps of each house. Thus, in addition to the interface of signs with houses and that of planets with signs, each chart has the interface of planets with houses as a set of factors worthy of astrological interpretation.

If a planet falls late in a house, within 2-3º of the cusp of the following house, it is interpreted as strongly in the following house. Robert Pelletier has argued that the houses are their beginning cusps, and the proximity of a planet to one or another of these points determines its house placement; but that is not the prevailing view.


House Division Methods

The different methods of dividing up the Horoscope into houses are called house systems, and have been categorised by John Filbey into three types: (1) the Ecliptic Systems, which trisect the four quadrants of the horoscope based on a measurement of space after they have been projected onto the ecliptic; (2) the Space Systems, which trisect the quadrants of the horoscope based on a measurement of space before they are projected onto the ecliptic; and (3) the Time Systems, which trisect the quadrants of the horoscope based on the measurement of the amount of time taken for each degree of the celestial ecliptic to pass between two angles around the horoscope.

The Ecliptic Systems include the Equal House System, which projects only the horizon onto the ecliptic, ignoring the meridian, then divides the ecliptic starting from the Ascendant into twelve equal thirty-degree houses; the Whole Sign System, derived as the Equal House system but with the houses rounded up to fill an entire sign each; and the Porphyry system, which projects the horizon and meridian onto the ecliptic, delimiting the quadrants with reference to all four angles, but then trisects each quadrant on the ecliptic.

The Space Systems include the Campanus System, which trisects each quadrant of the Prime Vertical then projects every cusp so derived onto the ecliptic; the Regiomontanus System, which like the Equal House system ignores the Zenith and Nadir, but instead projects the Ascendant onto the Celestial Equator, divides the equator into twelve equal segments starting from the Ascendant, then re-projects the resultant house cusps onto the ecliptic; and the Morinus system which is identical to Regiomontanus except for using the Equatorial Ascendant instead of the projected birthplace Ascendant.

The Time Systems include the Placidus System, which is based on the projection of the angles onto the ecliptic followed by the trisection of two diurnal semiarcs (i.e. amounts of time required for any degree of the ecliptic to pass from one angle to the next) – one from the ASC to the MC (giving the 11th and 12th house cusps), and one from the IC to the ASC (giving the 2nd and 3rd cusps); and the Koch system, which is based on the trisection of a diurnal semiarc starting from the MC.

In all quadrant-based house systems it is only necessary to calculate four intermediate house cusps, as the other four are always opposite.


Continue to Part Two of Four…

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