Four planets in a different house
Two astrologers can read the same chart, agree on every planet's position to the arcsecond, and still disagree about where 4 of the 10 planets are. We computed it. And the system most software uses cannot answer at all for anyone born north of 66.56 degrees.
Anything in a violet panel we computed from DE421 ephemeris data. You can check it.
Anything on a gold rule was said by people, at a particular time. We say who, and when.
What a house system actually does
THE PART NOBODY EXPLAINSThe signs divide the zodiac. The houses divide the sky as it stood over one place at one moment, which is a different problem and a harder one.
Everything starts from two points, and both are astronomy rather than convention. The Ascendant is the degree of the ecliptic rising on the eastern horizon at that instant, and the Midheaven is the degree crossing the meridian overhead. Neither is disputed. Every system in use agrees about them.
The disagreement is about what to do next: how to get from those two points to twelve divisions. That is where the systems part company, and it is a choice, not a discovery.
A moment and a place, not a person. What the article shows is the shape of the disagreement, not whose chart it is.
The two answers
THIRTY DEGREES EACH, OR NOTWhole Sign takes the sign the Ascendant falls in and makes that the whole of the first house. Every house is then one sign: exactly thirty degrees, twelve times, no arithmetic beyond finding the Ascendant.
Placidus divides time rather than space. It takes the arc a degree travels between rising and culminating and cuts it into thirds, which produces houses of unequal size that depend on the latitude.
Neither is wrong. They are answers to two different questions, and a chart drawn under one is not a chart drawn under the other with a rounding error.
Where the planets land
THE SAME SKY, TWICEHere is the same chart read both ways. Every position is identical, because the positions are not what is at issue.
| Planet | Position | Whole Sign | Placidus |
|---|---|---|---|
| Sun | Pisces 24°53′ | 9 | 10 |
| Moon | Gemini 18°17′ | 12 | 12 |
| Mercury | Pisces 28°32′ | 9 | 10 |
| Venus | Pisces 20°18′ | 9 | 9 |
| Mars | Virgo 27°31′ | 3 | 4 |
| Jupiter | Aquarius 11°51′ | 8 | 8 |
| Saturn | Aries 8°19′ | 10 | 10 |
| Uranus | Aquarius 7°18′ | 8 | 8 |
| Neptune | Capricorn 29°21′ | 7 | 7 |
| Pluto | Sagittarius 5°35′ | 6 | 5 |
4 of the 10 land in a different house. Not a different degree, a different house, which in practice means a different area of life.
This is worth sitting with, because it is the thing that makes house systems more than a technicality. If a reading tells you something about your career and the planet it rests on is in your career house under one system and your reputation house under another, then the reading was never about the sky alone.
Every system agrees about where the planets are. They disagree about where the walls go.
And then there is the far north
WHERE ONE SYSTEM RUNS OUTPlacidus divides the arc a degree travels between rising and culminating. Above the polar circle, part of the ecliptic never rises or sets at all, so that arc does not exist, and there is nothing to divide.
This is not a subtle degradation. Asked for Placidus houses north of that line, the independent library we check our work against returns an error rather than a number.
| City | Latitude | Largest house |
|---|---|---|
| Athens | 37.98° | 38.77° |
| London | 51.51° | 47.64° |
| Reykjavik | 64.15° | 76.52° |
| Rovaniemi | 66.50° | 62.51° |
| Tromso | 69.65° | - |
| Longyearbyen | 78.22° | - |
Note Reykjavik, still inside the limit and already carrying a house of more than seventy degrees, two and a half times the size of a Whole Sign house. Then it stops. We found the edge by bisection rather than quoting it: 66.56 degrees, which is the polar circle.
So we counted how general the problem is, rather than trusting anyone's summary of it.
Three of 24, and the most widely used system in the English-speaking world is one of them. Whole Sign is not: it needs only the Ascendant, which exists at every latitude short of the pole itself.
Which we use, and why we are saying so
OUR OWN CHOICE, DECLAREDThis app computes Whole Sign houses and no others. That is a position, not a neutral fact, and an article comparing two systems written by people who implement one of them should say so on the page rather than leave you to find out.
The reasons are the ones above. It is the oldest system, it is defined everywhere on Earth, and its houses do not change size depending on how far north you were born. The cost is real: it puts the Midheaven somewhere other than the tenth house cusp, which practitioners trained on Placidus find genuinely awkward.
What we will not do is show you a chart without telling you which set of walls it was drawn with.
Where the two systems came from
THE INTERPRETATION, AND ITS HISTORYFrom here down we are not measuring. We are telling a story, with names and dates, and with one caveat we will come back to at the end.
Whole Sign is thought to be the oldest system of house division, appearing in the Hellenistic tradition somewhere around the first or second century before Christ. For a very long stretch it was simply what houses meant.
Then it disappeared from the West so thoroughly that by the twentieth century western astrologers did not know it had existed. Its return is recent and traceable: Project Hindsight, founded in 1993 by Robert Schmidt, Robert Hand, Robert Zoller and Ellen Black, set out to translate the surviving Hellenistic texts, and what those translations showed was that the ancient astrologers had all been using whole signs. Hand began popularising the technique from the mid-1990s.
Placidus de Titis was an Olivetan monk and a professor of mathematics, physics and astronomy. The tables associated with him, Tabulae primi mobilis, appeared in 1657.
He did not invent the method that carries his name, and said so. The attribution runs back further, though the sources disagree about how far: one line credits the twelfth-century writer Abraham Ibn Ezra with identifying it as the system Ptolemy used, another places its first appearance in thirteenth-century Arabic literature, and a printed version exists from 1602, before Placidus published anything. What is agreed is that the name is younger than the method.
The story usually told is that Placidus became the standard because its tables were the ones a working astrologer could afford. R. C. Smith, publishing as Raphael, put Placidus tables into a popular almanac in 1821, and generations then computed houses the way the book in front of them made easy.
That story is documented and it is also disputed. Placidus had already gained ground through the seventeenth century, well before the cheap tables existed, so the honest version is that the almanacs reinforced a dominance rather than creating it. We would rather give you the argument than the slogan.
One thing about all of that deserves saying plainly, because it is easy to hide behind confident prose. The astronomy in this article is measured and you can check every figure. The history is not of the same grade: the best available sources for it are encyclopaedic and practitioner ones, and there is very little peer-reviewed history of science to lean on. We have said who claims what, and where they disagree, precisely so you can weigh it yourself.
How these numbers were arrived at
METHOD, AND ITS CHECKThe positions come from NASA's DE421 ephemeris data, by the same machinery that computes your birth chart inside the app. The Whole Sign houses are ours. The Placidus houses, and every other system counted above, come from Swiss Ephemeris, an entirely independent implementation, which is the point: this is our arithmetic against somebody else's, not against itself.
A comparison of houses is only worth anything if the two sides agree about where the horizon is to begin with, so that is checked first.
Arcseconds, on a quantity that moves a degree every four minutes. The two systems are being compared from the same starting point, which is what makes the disagreement about houses a real disagreement rather than an artefact.
Sources
SO YOU CAN CHECK THEM YOURSELF- Positions and angles: JPL DE421. House systems and the polar-circle survey computed with Swiss Ephemeris 2.10.03.
- Placidus de Titis (1603 to 1668), Olivetan monk and professor of mathematics; Tabulae primi mobilis, 1657.
- Project Hindsight, founded 1993 by Robert Schmidt, Robert Hand, Robert Zoller and Ellen Black, and the translations that returned whole sign houses to western practice.
- R. C. Smith (Raphael), almanac carrying Placidus tables, 1821.
- A note on the history: the sources available for it are encyclopaedic and practitioner ones rather than peer-reviewed history of science, and they disagree in the places we have flagged. The astronomy above is measured; the history is reported.
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