Regiomontanus Houses

Definition

Regiomontanus is one of the ways of dividing a chart into twelve houses. It splits the celestial equator — the projection of Earth's equator onto the sky — into three equal parts per quadrant, then carries those divisions onto the zodiac using great circles drawn through the north and south points of the horizon. The system is named after Johannes Müller (1436-1476), a German mathematician known by his Latin name Regiomontanus, whose 1490 work Tabulae directionum profectionumque first made the calculation widely available. In this system the Ascendant and Midheaven fall exactly on the 1st and 10th house cusps.

In Tradition

In medieval and Renaissance Western astrology, Regiomontanus became the leading house system once its calculation tables were published — it displaced the older Alchabitius system simply because no comparable tables existed for the rival Campanus method. In modern practice it is most closely tied to horary astrology, the branch that answers a specific question from a chart cast for the moment it was asked. William Lilly's Christian Astrology (1647) used Regiomontanus throughout, and it is still a common choice in today's traditional-revival horary community.

In Practice

To build the in-between cusps, a Regiomontanus chart splits the day-arc and night-arc of the celestial equator into thirds, then carries those points onto the zodiac with great circles drawn through the north and south points of the horizon. The result is houses of unequal size that work reasonably well across most inhabited latitudes, with the cusps shifting in response to how far north or south the birthplace is. Modern astrology software supports the system directly. At very high latitudes it can produce extreme distortions, as all quadrant systems do; whole signs or equal houses are commonly used instead in those cases.

Historical Origin

Holden records that Regiomontanus's directional tables were published in 1490 at Augsburg by Erhard Ratdolt, and that the field shifted away from Alchabitius soon after. The system was carried forward by Renaissance Latin astrologers and made canonical for seventeenth-century English horary by William Lilly's Christian Astrology (1647). Modern surveys by Hand, Holden, and Houlding treat it as the main traditional alternative to Placidus.

Further Reading