Regiomontanus

Meaning

Regiomontanus divides the sky by the celestial equator, the projection of the Earth’s equator onto the sky, along which the stars turn each day. Starting from the point where the equator meets the eastern horizon, it cuts the equator into twelve equal arcs of 30°. Each mark is then carried onto the zodiac along a great circle through the north and south points of the horizon. Where that circle crosses the ecliptic lies a house cusp.

Precisely: the house circles are the same as in Campanus, twelve great circles through the north and south points of the horizon. Campanus spaces them evenly along the prime vertical; Regiomontanus spaces them evenly along the equator. The horizon gives the Ascendant and the Descendant, the meridian gives the Midheaven and the IC, and the other circles give the eight intermediate cusps, opposite cusps being 180° apart.

Because the equator is the circle of the daily turn, Regiomontanus sits between the space-based and the time-based systems. Its houses are spaced evenly in the sky’s rotation as seen from the birthplace, yet they are drawn with fixed circles, not with each degree’s own rising time. Its cusps usually differ from those of Placidus by a few degrees: up to about 5° at 45° of latitude.

Its houses grow unequal with latitude, less than in Campanus but more than in Placidus. At 45° they range from about 16° to 54° of the zodiac, at 60° from about 7° to 95°. Inside the polar circles, the cusps can run backwards round the zodiac. Near the equator it gives almost the same cusps as Placidus and Campanus, and on the equator itself they coincide.

In practice

• The classic system of horary astrology. Many horary astrologers use it, following William Lilly, whose Christian Astrology (1647) casts its charts in Regiomontanus houses.
• Traditional practice. Some astrologers who work with the methods of the Renaissance and the 17th century keep it for consistency with their sources.
• High latitudes. For births far north or south, its houses become very uneven, and comparing with Porphyry or Equal houses can help.

Origin and history

Regiomontanus was the name taken by Johannes Müller of Königsberg (1436–1476), one of the leading astronomers of 15th-century Europe. His Tabulae directionum, tables for primary directions written in the 1460s and printed in 1490, made this division easy to compute. It then took the place of Alcabitius’ system as the usual one in Europe. William Lilly used it for the horary charts of Christian Astrology in 1647, and the modern revival of horary astrology, which leans on Lilly’s book, brought it back into common use. Historians such as John North have traced how it was calculated and adopted.

How Ulune calculates it

Choose Regiomontanus in the birth form’s options. The Swiss Ephemeris computes the cusps with its code R. The Ascendant, the IC, the Descendant and the Midheaven are the cusps of the 1st, 4th, 7th and 10th houses.

Regiomontanus is computed at every latitude, so Ulune never replaces it with Porphyry. Inside the polar circles, its cusps can come out of zodiac order. At some times of day there, the Swiss Ephemeris also puts its Midheaven opposite the point Equal or Porphyry houses would give. Ulune keeps both as the Swiss Ephemeris gives them, and reads the chart’s angles from them. In a composite chart in Regiomontanus, the angles are the midpoint angles and the other cusps keep, inside each quadrant, the average of their places in the two charts.

Correspondences