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Placidus houses
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What it is
Placidus is a quadrant house system based on time. Instead of cutting a circle in the sky into equal pieces, it follows each degree of the zodiac on its own daily journey across the sky and divides that journey into thirds.
The four angles are the cusps of the angular houses: the Ascendant opens the 1st house, the Imum Coeli the 4th, the Descendant the 7th and the Midheaven the 10th. The other cusps are found between them.
How it is worked out
Every degree of the zodiac rises in the east, climbs to the meridian and sets in the west. The time it takes to go from the horizon up to the meridian is its semi-arc. Placidus defines the cusps by fractions of that time:
- the cusp of the 12th house is the degree that has completed one third of its journey from rising to culmination;
- the cusp of the 11th house is the degree that has completed two thirds;
- the cusps below the horizon (the 2nd and 3rd) are found the same way along the night-time half of each degree's journey;
- the opposite cusps (5th, 6th, 8th, 9th) lie directly across the chart.
Because each degree is measured against its own time, there is no single circle being divided, and the houses come out uneven: some quadrants hold long houses and others short ones, depending on the latitude and the signs on the angles. Some signs may be wholly contained in a house (an intercepted sign), with another sign holding two cusps.
Where it comes from
The method was known to the Italian mathematician Giovanni Antonio Magini in the late sixteenth century; the Benedictine monk Placidus de Titis (1603–1668) published it and argued it was what Ptolemy had intended. His works were placed on the Catholic Index in 1687, but they found readers in England, were translated in the late eighteenth century, and in the nineteenth century the popular Raphael's ephemerides printed tables of houses calculated by Placidus. Since nearly every astrologer then cast charts from those tables, it became the default of modern Western astrology — less a verdict on its merits than a fact of publishing history.
Strengths and weaknesses
- Its supporters value the way it follows the sky's actual daily motion, and the century of modern literature written in it: when a book describes a planet "on the cusp" of a house, it usually means a Placidus cusp.
- Its critics point to the uneven houses and to its behaviour far from the equator. Above roughly 66° of latitude — inside the Arctic and Antarctic circles — some degrees of the zodiac never rise or set, so the question Placidus asks has no answer, and the system fails altogether. Well before that, at the latitudes of Scandinavia or Scotland, houses can become very large or very small.
For births at high latitudes many astrologers switch to equal houses, whole sign houses or Porphyry.
In a reading here
Placidus is the house system Viastaro uses unless another is chosen. It can be changed, as a default for the account and per person in the reading settings, to Koch, whole sign, equal, Regiomontanus, Campanus or Porphyry. Horary readings are the exception: they are always cast in Regiomontanus, the system of the horary tradition.