Alcabitius

Meaning

Alcabitius divides time, but along the celestial equator rather than along the zodiac. It takes the degree rising at birth, the Ascendant, and asks how long that degree will take to climb from the horizon to the meridian. That time is cut into three equal parts, and each mark gives a house cusp above the horizon. Below the horizon, the same is done with the time the Ascendant degree spent under the earth.

Precisely: the diurnal semi-arc of the Ascendant degree is measured in right ascension, along the equator. Starting from the right ascension of the meridian, one third and two thirds of that arc give two points on the equator. The hour circles through those points, great circles through the celestial poles, cross the ecliptic at the cusps of the 11th and 12th houses. The nocturnal semi-arc gives the 2nd and 3rd the same way, and opposite cusps are 180° apart. The four angles are the cusps of the 1st, 4th, 7th and 10th houses.

Where Placidus gives every degree its own semi-arc, Alcabitius uses a single one for a whole quadrant, the Ascendant’s. The result is a time-based system that behaves much like Porphyry. At mid-latitudes its cusps usually lie within about 3° of Porphyry’s, and its houses stay moderate far from the equator. At 60° of latitude they range from about 13° to 49° of the zodiac, where Placidus houses reach 85°.

It also keeps working inside the polar circles, where its cusps stay in zodiac order. Its limit, for those who prefer Placidus, is that it measures the whole quadrant with one degree’s semi-arc, a simplification of the idea of time-based houses.

In practice

• Medieval astrology. Some astrologers who study medieval Arabic and Latin texts use it to stay close to their sources.
• Moderate houses at high latitudes, which makes it a time-based alternative to Placidus for births far north or south.
• Close to Porphyry. At mid-latitudes a planet rarely changes house between the two; near the cusps, it is worth checking.

Origin and history

The system takes its name from al-Qabīṣī, latinised as Alcabitius, a 10th-century astrologer and mathematician who worked at the court of Sayf al-Dawla in Aleppo. His Introduction to astrology, dedicated to that ruler, was translated into Latin in the 12th century and became one of the most read astrological textbooks of medieval Europe. The house division known by his name was the most common one in late medieval Europe, until Regiomontanus’ tables, printed in 1490, made his own system the new standard. John North’s Horoscopes and History (1986) and Deborah Houlding’s history of the houses (1998) follow that change.

How Ulune calculates it

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

Alcabitius is computed at every latitude, so Ulune never replaces it with Porphyry; inside the polar circles its cusps stay in zodiac order. In a composite chart in Alcabitius, the angles are the midpoint angles and the other cusps keep, inside each quadrant, the average of their places in the two charts.

Correspondences