What a house system changes
A house system converts local time and coordinates into twelve sectors. The chosen method can change cusp degrees, house sizes and the house assigned to a planet near a boundary. It does not change a planet’s zodiac longitude for the same moment.
Astro Legacy sends the selected system code to the calculation engine. Keep the system visible when saving or comparing a result; two charts that use different methods are not directly identical.
Systems available in Astro Legacy
| System | Code | Practical distinction |
|---|---|---|
| Placidus | P | Time-based quadrant system and the product default |
| Krusinski | U | Quadrant-style system developed by Bogdan Krusiński |
| Koch | K | Time-based quadrant system using a different construction |
| Equal | E | Twelve equal 30° houses beginning from the Ascendant |
| Whole Sign | W | The whole rising sign becomes the first house, followed sign by sign |
| Regiomontanus | R | Quadrant system based on divisions related to the celestial equator |
| Campanus | C | Quadrant system based on divisions of the prime vertical |
| Porphyry | O | Divides the arcs between angles into three equal sectors |
The descriptions identify construction families, not a ranking of accuracy. Traditions choose systems for historical, philosophical and practical reasons.
Placidus, Equal and Whole Sign
Placidus produces unequal houses and can behave unusually at extreme latitudes. Equal houses preserve the Ascendant degree as the start of the first house and set every house to 30°. Whole Sign uses sign boundaries for houses; the Ascendant remains an angle within the first sign rather than necessarily its cusp.
These methods can place the same planet in adjacent houses. When comparing interpretations, first check whether the underlying house system changed.
Why exact birth time matters
Earth rotates roughly one degree every four minutes relative to a 24-hour cycle, although the actual effect on chart points depends on latitude and geometry. Even a modest time error can move the Ascendant and house cusps. Near a sign or house boundary, the label can change.
If the time is unknown:
- use the unknown-time option rather than pretending noon is verified;
- treat ASC, DESC, MC, IC and houses as approximate;
- give more weight to planet-to-planet aspects that change more slowly;
- avoid rectifying the time from one life event without a careful method.
How to choose
Start with the tradition or astrologer whose method you intend to follow. Placidus is a useful baseline because it is Astro Legacy’s default; Whole Sign is useful for a sign-based traditional approach; Equal offers a simple degree-based structure. Consistency is more useful than switching systems until one interpretation feels preferable.
Common questions
Does changing the system change the zodiac signs of planets?
No. It changes house structure, not planetary longitude.
Is Placidus objectively best?
No. It is the product default, not a claim of universal superiority.
Can exact birth time solve every difference?
It improves time-dependent calculation, but different house systems can still produce different cusps from the same accurate time.