Same sky, different slices
Signs and houses answer different questions. Your signs say where each planet was along the zodiac. Your houses say where it was relative to your own horizon and meridian, at your birthplace, at your birth moment: rising in the east, high overhead, setting in the west or below the ground. Every house system agrees on the signs and degrees of your planets. They disagree only on where to draw the twelve house boundaries.
There are many systems. The ones you are most likely to meet are Whole Sign, Placidus, Equal, Porphyry and Koch. If one app says your Venus is in the 12th house and another says the 1st, neither has made a mistake; they are using different systems.
Aurae uses Whole Sign houses everywhere: in your chart, in the Moon’s daily house, and in transit timing. The rest of this page explains what that means and when it changes your reading.
How Whole Sign houses work
The sign rising on the eastern horizon at your birth, your Rising sign, is the entire 1st house, from 0° to 30° of that sign. The next sign is the 2nd house, the one after that the 3rd, and so on round the zodiac. Each house is exactly one sign.
Example (hypothetical chart): Ascendant at 20° Leo. Then all of Leo is the 1st house, Virgo the 2nd, Libra the 3rd, and so on to Cancer as the 12th. A Moon in Libra is in the 3rd house; a Saturn in Aquarius is in the 7th.
Three things follow from this:
- ✦Houses are always 30°, at any latitude, from the equator to the Arctic.
- ✦A planet’s house is the count from your Rising sign to the planet’s sign. If you know both signs, you can work it out by hand.
- ✦Birth time matters only through the Rising sign. The Ascendant takes anywhere from under an hour to over three hours to cross a sign, depending on the sign and your latitude. If a time error does not change your Rising sign, it does not change any house.
In Whole Sign, the Ascendant degree and the Midheaven (MC) are still calculated and read, as sensitive points, but they do not mark where houses begin.
How Placidus divides the sky
Placidus is a quadrant system. It uses four fixed points as house starts: the Ascendant degree begins the 1st house, the IC the 4th, the Descendant the 7th, and the MC the 10th. Then it splits each quadrant into three by time.
Every degree of the zodiac takes a certain time to travel from the eastern horizon up to the meridian. Placidus finds the degrees that have completed one third and two thirds of their own journey, and those become the cusps of the 12th and 11th houses. The same method below the horizon gives the 2nd, 3rd, 5th and 6th. Because degrees near the horizon move at different speeds depending on the sign and your latitude, the twelve houses come out unequal. At mid-latitudes one house can span well over 30° and another much less, a sign can be swallowed whole inside one house (an intercepted sign), and another sign can begin two houses in a row.
The system is named after Placido de Titi (Placidus de Titis), a seventeenth-century Italian monk and mathematician. Its spread in English-language astrology is usually credited to availability: from the nineteenth century, the widely sold Raphael’s Ephemeris and its companion tables of houses were calculated in Placidus, and for generations those tables were the affordable ready-made tables most astrologers owned. Placidus stayed the default when software arrived, which is why many apps still use it.
Where Placidus breaks down
Placidus depends on every degree of the zodiac rising and setting each day. Near the poles that stops being true. Above the polar circles, at about 66.5° north or south, some degrees of the zodiac never rise and others never set; they stay above or below the horizon all day. A degree that never crosses the horizon has no journey from horizon to meridian to divide, so for some birth times Placidus cannot produce cusps at all. The Koch system fails the same way.
This is not only a theoretical problem. Places such as Tromsø in Norway and Utqiaġvik in Alaska lie above the Arctic Circle. Astrology software has to fall back to another system for those births. Even somewhat south of the circle, Placidus houses become extremely stretched and squeezed.
Whole Sign, Equal and Porphyry houses can be calculated for any place on Earth.
Why Aurae uses Whole Sign
- ✦It is the oldest well-documented approach. Whole Sign is the default in the surviving horoscopes and manuals of Hellenistic astrology in the first centuries CE, and it is the traditional house method of Jyotish. The history is not completely tidy: some early authors also describe quadrant divisions, and how they were used is debated.
- ✦It works at every latitude, with no fallbacks and no unequal houses.
- ✦It is forgiving about birth time. Unless your Ascendant was near the edge of a sign, a time that is off by a few minutes changes nothing.
- ✦It keeps everything Aurae computes consistent. The Moon’s daily house in Aurae is simply the sign count from your Rising sign, so the Moon changes house when it changes sign. The love-timing calculator marks Venus and Jupiter moving through the signs of your 5th and 7th houses on the same basis.
House placements are part of the full chart on Aurae. The birth-chart calculator gives your Sun, Moon and Rising signs instantly. A free Aurae account saves your chart and shows your birth-chart wheel and Big Three, plus one placement from your chart each day. Pro lists every planet’s sign, degree and house — Chiron and the lunar nodes included — with your house cusps and solar return; personalized AI chart readings are part of Premium.
What changes for you
Most planets land in the same house in both systems. The ones that move are those near the Ascendant or near another sign boundary.
Worked example (hypothetical chart, Ascendant 20° Leo)
| Planet | Whole Sign house | Placidus house |
|---|---|---|
| Venus at 8° Leo | 1st: Leo is the Rising sign | 12th: it sits behind the Ascendant degree |
| Mercury at 3° Virgo | 2nd: Virgo is the next sign | 1st: the Placidus 2nd house begins later in Virgo |
Aurae checked this chart from the equator to 60° north: the Placidus 12th house begins around 21° Cancer, and the Placidus 2nd house begins between about 5° and 22° of Virgo depending on latitude, so both shifts hold throughout that range.
The pattern is general. A planet in your Rising sign but at an earlier degree than the Ascendant is in the 1st house in Whole Sign and the 12th in any system that starts the 1st house at the Ascendant degree. A planet early in the sign after your Rising sign can be in the 2nd house in Whole Sign and still the 1st in Placidus.
Equal and Porphyry houses
Equal houses also start at the Ascendant degree but make every house exactly 30°, so the MC floats like it does in Whole Sign. Porphyry, named after the third-century philosopher, keeps the four angles as cusps like Placidus but splits each quadrant into three equal arcs of the zodiac instead of by time. Both work at every latitude. In the example above, both also put Venus in the 12th house and Mercury in the 1st.
If a planet moves house, read it in its Whole Sign house on Aurae. The house themes themselves are the same in every system:
House systems: short answers
Which house system is more accurate?
None has been shown to be more accurate than the others. They are different ways of dividing the same sky, with different histories. Pick one for a clear reason, such as tradition, latitude or the techniques you use, and use it consistently.
Should I re-read my chart if I switch to Whole Sign?
Only the parts that move. Your signs, degrees and aspects are identical in every system. Check which planets change house, usually those near your Ascendant or near a sign boundary, and read those again.
Does the MC stay in the 10th house in Whole Sign?
Not always. By Aurae’s own calculation across every rising time, the MC lands in the 9th, 10th or 11th whole sign house anywhere within about 47° of the equator, north or south. Farther from the equator it can occasionally land in the 8th or 12th. Whole Sign astrologers read the MC as an important point in its own right, in whichever house it falls.
Do transits work differently in Whole Sign?
Only in which house they activate. In Whole Sign, a transiting planet changes house exactly when it changes sign, so transit houses are easy to follow. In Placidus, it changes house at each cusp degree, which differs from chart to chart.
Can I see Placidus houses on Aurae?
No. Aurae calculates every chart with Whole Sign houses in the tropical zodiac. It does not offer Placidus houses or sidereal charts. For how the sidereal zodiac changes houses, see why your sign is different in Vedic astrology.