Why Placidus Houses Differ in Size: Wide and Narrow Houses Explained

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Look at almost any Placidus chart and the twelve houses are visibly different sizes. One house might cover 17° of the zodiac and its neighbour 45°. That is not a drawing error or a sign that something went wrong with the birth data. It follows directly from how Placidus divides the sky, and it changes with the latitude of the birthplace and the time of day. This page explains the mechanism, shows computed examples, and covers what house size does and does not mean for interpretation.

On Astrologist.com: the free birth chart uses Placidus houses by default. For a birthplace at an absolute latitude greater than 66° north or south it uses Equal houses from the Ascendant instead, and says so on the chart; exactly 66° remains Placidus. The wheel draws the cusps at their real positions, so unequal houses show up as unequal slices.

Placidus divides time, not zodiac degrees

Each degree of the zodiac rises in the east, climbs to the Midheaven, sets in the west and passes under the chart to the IC, once a day. Placidus takes the time each degree needs to get from the eastern horizon up to the meridian, and splits that time into thirds. The degree that has completed one third of that climb at the moment of birth marks the 12th cusp; the degree that has completed two thirds marks the 11th. Below the horizon the same is done with the time from the IC up to the Ascendant, which gives the 3rd and 2nd cusps.

The calculator on this site follows exactly that construction. It computes the Ascendant and Midheaven, finds the 11th, 12th, 2nd and 3rd cusps by trisecting these time arcs, and then sets the remaining cusps directly opposite: the 5th opposite the 11th, the 6th opposite the 12th, the 8th opposite the 2nd and the 9th opposite the 3rd, with the Descendant and IC opposite the Ascendant and Midheaven. Two consequences follow:

• Opposite houses always have the same width. If your 3rd house spans 34.36°, so does your 9th.
• The four quadrants usually differ. The arc from the Midheaven to the Ascendant (the 10th, 11th and 12th houses together) is not fixed at 90°. Each quadrant is then split into three houses that are themselves unequal.

Equal time does not mean equal zodiac degrees, for two reasons. The zodiac is tilted against the celestial equator, so the same stretch of time carries different amounts of the zodiac across the horizon depending on which part is rising. And away from the equator, some parts of the zodiac spend far longer above the horizon than others.

Even at the equator, houses are not exactly 30°

At 0° latitude every degree is above the horizon for half a day, so the time arcs are all the same length. The tilt of the zodiac still makes the house widths uneven, just less so. In a sample of one calendar day (27 August 1991, every 4 minutes, 360 moments, which brings every sign onto the Ascendant), Placidus house widths at the equator ran from 27.62° to 32.57°.

Latitude stretches the differences

Moving away from the equator, the gap between the fastest- and slowest-rising parts of the zodiac grows, and so does the spread of house widths. Same sample day and method, longitude 5.12° E, Placidus calculated with the site's own code:

These figures describe one sampled day at each latitude, not every possible chart, but the trend is the point: by the mid-60s a single Placidus house can stretch over more than four signs while its neighbour covers a few degrees. That is one reason the site switches to Equal houses above 66°. Chart angles at high latitudes explains the fallback and why its MC and IC labels mark the 10th and 4th cusps rather than the true angles.

The southern hemisphere shows the same spread at the same latitude: at 52.09° S the sampled widths ran from 15.42° to 61.57°.

Which sign is rising matters

At a given latitude, the size of the houses around the Ascendant depends mostly on how quickly the rising part of the zodiac crosses the horizon. In the Utrecht sample, Aquarius was on the Ascendant for 17 of the 360 four-minute samples, roughly an hour and ten minutes, while Libra held it for 43 samples, close to three hours. Averaged by rising sign, the 1st house was:

• about 61° wide with Aquarius rising, 54° with Capricorn or Pisces;
• about 16° wide with Cancer rising, 18° to 19° with Leo or Gemini.

At 52.09° S the same averages appear for the opposite signs: about 61° with Leo rising and about 16° with Capricorn rising. Astrologers call the quickly rising signs "signs of short ascension" and the slowly rising ones "signs of long ascension", and which is which reverses between hemispheres.

Through one day in Utrecht

Birth time changes house widths as much as latitude does. Here are six charts for the same date and place, 27 August 1991 in Utrecht (52.0907° N, 5.1214° E), local summer time:

The 06:55 chart is Lotte's, the fictional example used in how to find your house cusps, where the full cusp table is set out. Across these six times, the arc from the Midheaven to the Ascendant ranged from 54.64° (17:12) to 125.73° (00:00), against the 90° an evenly divided chart would have.

What house size means, and what it does not

A wide house is not a stronger or more important house in itself. It spans more of the zodiac, so it is more likely to contain planets, and a narrow house is more likely to be empty. That is geometry, not emphasis. Two practical points follow from it:

• Empty houses are common. With ten planets and twelve houses, at least two are always empty, and narrow houses are the likelier candidates. Empty houses explains how they are read.
• Size creates interceptions and repeated signs. A house wider than 30° can contain a whole sign that never touches a cusp, which is an intercepted sign. A house narrower than 30° can begin and end in the same sign, which puts the same sign on two house cusps.

The size of a house may still say something about how a chart is read in practice. A planet near the middle of a very wide house sits far from either cusp, so its house placement is robust to small birth-time errors; in a narrow house, a few minutes of clock time can move a planet across a cusp. How accurate a birth time needs to be shows how to test that.

Equal houses above 66°

Equal houses start at the Ascendant and give every house exactly 30°, so the size question disappears. On Astrologist.com that applies only when the absolute latitude of the birthplace is greater than 66°, and the chart names the house system it used. Other house systems in wider astrology divide the chart in still other ways, so a chart from a site using a different system can show different cusps and different widths. If you compare charts, check the house system first.

Want to see your own house widths? Generate your free birth chart with an exact birth time and look at the slices of the wheel, or take the numbers from a cusp table as described in the cusp guide. To talk through what a crowded wide house or an empty narrow one could mean in your chart, Ask the Astrologist.

Related articles

• How to Find Your House Cusps: All Twelve, by Degree
• Intercepted Signs in Astrology
• The Same Sign on Two House Cusps
• Empty Houses in Astrology
• Angular Houses in Astrology
• Chart Angles at High Latitudes