How Placidus houses are calculated
Understand Placidus semiarcs, unequal house widths and polar limits, with a worked cusp comparison and a free house calculator.
Read the guide ↗THE SKY DEGREES REFERENCE
One moment. Eight ways to divide it.
House systems use different geometric rules to divide the local sky. Changing a house system can move a planet to another house without changing its zodiac sign. Keep the birth details and zodiac fixed to make a useful comparison, and distinguish the true Midheaven from the tenth cusp.
Compare one setting at a time.
Open the house calculator, calculate with one method, then change only the house system. Record the twelve cusps and any placements that move. The true ASC, MC, DSC and IC are returned separately. Placidus and Koch are unavailable at or beyond the polar circle; other degenerate geometries can also be rejected.
Open the house calculator ↗How whole sign houses work
See how the rising sign becomes the first house, why the MC stays separate, and how whole sign differs from equal houses in a worked example.
Read the guide ↗How equal houses are calculated
Calculate equal house boundaries from the Ascendant and see why the tenth cusp can differ from the Midheaven, with a numerical example.
Read the guide ↗How Alcabitius houses are constructed
Explore the Alcabitius house system: divide the Ascendant’s semiarcs, project right ascension onto the zodiac, and compare a worked cusp example.
Read the guide ↗How Koch houses are calculated
Understand Koch house cusps through the culminating point’s semiarc, a numerical comparison with Placidus, and explicit polar restrictions.
Read the guide ↗How Porphyry divides the chart
Follow a worked Porphyry calculation from MC to Ascendant, see why house widths differ between quadrants, and understand geometry limits.
Read the guide ↗How Regiomontanus houses are constructed
See how Regiomontanus projects celestial-equator divisions onto the zodiac, compare Campanus cusps, and understand polar placement limits.
Read the guide ↗How Campanus divides the local sky
Understand the Campanus prime-vertical construction, compare its cusps with Regiomontanus, and read a worked example with polar limitations.
Read the guide ↗Keep the setting with the result.
Record the birth time, location, zodiac and house system when you compare charts. A changed sign label or house placement can reflect a changed convention. If the recorded time is unknown, an exact Ascendant or house cannot be recovered by guessing.
Why chart settings change the result ↗