Half-Sum

haf sum

Definition

Half-sum is another name for midpoint: the zodiac point that is the average of two planetary longitudes. The direct half-sum lies between the two planets on the shorter arc; the inverse half-sum is the point 180° opposite it. Both count as sensitive spots in midpoint-based methods. The original German term is Halbsumme; "half-sum" is the standard English rendering used in the Cosmobiology and Uranian schools.

In Tradition

In Cosmobiology and Uranian astrology, the half-sum — the midpoint — of any two planets is read as a sensitive point that takes on the combined nature of those two planets, so any natal planet or moving planet contacting it is read as switching on that combined meaning. The doctrine is most fully worked out in Reinhold Ebertin's framework, where every planetary pair is given a structured set of "Combination of Stellar Influences" readings to apply wherever the half-sum is touched.

In Practice

Astrologers find the half-sum by adding the two planetary longitudes and halving — reducing modulo 360° if the total runs over. They then check both the direct and the inverse half-sum against natal planets and against moving planets, usually with very tight orbs of 1° to 1.5°. On the 90° dial, all four cardinal-axis versions of the half-sum line up visually, so a single dial mark catches contacts to the direct point, the inverse point, and the squares to both. The astrologer then blends the planetary-pair meaning — Sun/Moon as integration, say, or Mars/Saturn as endurance under restriction — with the contacting planet to read what is being set off.

Historical Origin

The half-sum, or midpoint, as a live sensitive point originates in Alfred Witte's Hamburg School (early twentieth century, Hamburg) and was systematized for Cosmobiology by Reinhold Ebertin in Kombination der Gestirneinflüsse (1940; English The Combination of Stellar Influences, AFA 1972, trans. Brummund). The technique is now standard in Cosmobiology, Uranian, and modern psychological-astrology midpoint work.

Definition

In Tradition

In Practice

Historical Origin

Further Reading