The houses divide the local sky, as seen from the birthplace at the birth time.
Because the Earth turns, they make a full circle in twenty-four hours, which sets them apart from the signs, fixed on the zodiac. The first sector starts at the rising sign, the degree of the ecliptic rising on the eastern horizon; the other eleven follow in sequence, first below the horizon, then rising in the west.
The systems differ in how they draw the boundaries. Whole Sign houses, the oldest, make each sign a house. Equal houses measure 30 degrees from the rising sign. Porphyry divides each quarter of the sky into three equal parts. Regiomontanus divides the celestial equator, Placidus the time each degree takes to rise to the Midheaven. These last two give houses of unequal widths.
The choice changes neither the planets’ signs nor the rising sign: at most it can move a planet into the neighboring house, when it is close to a boundary. Placidus becomes impossible near the poles, where some degrees never rise: the site then switches to Porphyry beyond 66° of latitude. It offers Placidus by default, while Whole Sign and Equal houses are available as options.
Family
The chart
The diagram
Six ways to divide the sky
Read next
Rising sign and Midheaven
History, debates, and sources
A little history
The use of whole signs goes back to Hellenistic astrology, which Vettius Valens illustrates in his Anthologies, in the 2nd century.
Porphyry, a century later, describes dividing each quarter into three equal parts. Regiomontanus spreads across Europe, in 1490, a system based on the celestial equator. Placidus de Titis publishes his own in 1657, based on time, which André Barbault uses in his Traité pratique d’astrologie of 1961. It is the most widespread in modern French astrology.
Sources
5
Oldest
Vettius Valens, 2nd century
Most recent
André Barbault, 1961
What is debated
No system has unanimous support.
Supporters of Placidus stress its precision and its reach. Supporters of Whole Sign houses see it as the method most faithful to ancient texts and the simplest. Equal houses appeal by their regularity. Quadrant systems, finally, run into a problem near the poles. Each remains defensible, depending on what you expect from the houses.
Schools do not all agree: the site sets out the positions without deciding for you, and states the setting it uses by default.
Where this concept comes from
The authors and texts that establish or discuss this concept, with the passage when it is known.
2nd centuryVettius ValensAnthologies, whole work
Use of whole signs: each sign forms a house.
3rd centuryPorphyryIntroduction to the Tetrabiblos, whole work
Divides each quadrant between the angles into three equal parts.
1490RegiomontanusTabulae directionum, whole work
Spreads across Europe a system based on dividing the celestial equator.
1657Placidus de TitisTabulae primi mobilis, whole work
System based on the division of time: the most widely used in France today.
1961André BarbaultTraité pratique d’astrologie, whole work
Reference work of modern French astrology, which uses Placidus.
The diagram’s figures are calculated by the site’s engine (Astronomy Engine) or taken from the recorded facts, never copied by hand.
Six ways to divide the sky
House systems: principle, origin, and what the site offers
System
Principle
Origin
On the site
Placidus
Division of the time each degree takes to travel from the horizon to the meridian
Placidus de Titis, 1657
Default · impossible near the poles
Porphyry
Each quadrant between two angles cut into three equal parts
Porphyry, 3rd century
Optional; takes over from Placidus beyond 66°
Equal houses
Twelve houses of 30° from the ascendant
Hellenistic tradition
Optional
Whole Sign
The rising sign forms the 1st house, the next sign the 2nd house…
Vettius Valens, 2nd century
Optional
Regiomontanus
Division of the celestial equator into twelve equal parts
Regiomontanus, 1490
No · impossible near the poles
Koch
Division of time starting from the Midheaven
Walter Koch, 20th century
No · impossible near the poles
Frequently asked questions: house systems
Which house system should I choose?
There is no single right answer. Placidus is the most common in France, Whole Sign the oldest, Equal houses the simplest. The site offers Placidus by default, and lets you compare the others in the chart settings.
Why doesn’t Placidus work near the poles?
Because it divides the rising time of each degree, and near the poles, from about 66° of latitude, some degrees no longer rise or set. The calculation then has no solution. The site switches to Porphyry beyond 66°.
Why do my houses change from one website to another?
Because each website chooses its own default system: Placidus, Whole Sign, Equal houses… The signs and the rising sign stay the same, but the house boundaries move, and a planet close to a boundary can change house.