House systems, explained
A house system is the rule for slicing the sky into twelve houses — the areas of life a chart maps planets onto. The planets' positions don't change between systems; only where the house lines fall. Because that choice changes which house a planet lands in, we label every chart with the system it used.
What houses are
The twelve houses are twelve segments of the sky, anchored to the horizon and meridian at your exact time and place of birth. The first house begins at the Ascendant — the point rising on the eastern horizon. Where the other eleven boundaries fall depends on the house system, and that is a genuine modeling choice, not a fact of the sky.
The systems we offer
- Placidus
- Placidus (our default) divides the houses by time — how long a degree takes to rise from the horizon to the midheaven. It's the most widely used system in modern Western astrology, which is why we default to it, though it distorts at high latitudes.
- Whole Sign
- Whole Sign assigns one whole zodiac sign to each house, starting from the sign of your Ascendant. It's the oldest system, simple and stable, and it never breaks down at extreme latitudes.
- Equal
- Equal houses are exactly 30° each, measured from the Ascendant. It keeps the Ascendant as the first-house cusp but spaces the rest evenly, sidestepping the latitude distortion of time-based systems.
- Porphyry
- Porphyry divides the arc between each angle into three equal parts. It's a straightforward space-based system and a common middle ground between quadrant and equal approaches.
- Koch
- Koch, like Placidus, is a time-based quadrant system popular in 20th-century astrology. It emphasizes the birthplace's horizon and shares Placidus's breakdown at high latitudes.
Above the polar circle
Beyond about 66.5° latitude, the time-based quadrant systems (Placidus, Koch) stop producing valid houses — some houses collapse or invert. When a birth place is above that line, we fall back to Whole Sign houses and flag it clearly on the chart, rather than showing numbers we don't trust.
Why we always show the system
Because the house system changes which house a planet falls in, the same birth data can yield different house placements under different systems. None is the single real chart — they're different lenses. So we label every chart with the system it used and let you switch, instead of hiding the choice.