Decanates A division of the signs into 10 degrees each of which is subtly different from one another due to the different rulers involved.

A one-third (ten-degree) sector of a sign. Each sign has three decanates: 0-10 degrees, 11-20 degrees and 21-30 degrees. Each decan has its own ruler. According to Alan Leo, each decan is divided into two faces, a positive and a negative, each with its own ruler. Decanates themselves are also known as faces. Decans originally derive from ancient Egytian astrology, where the decans were considered paramount, before being subsumed under the Chaldean 12-sign zodiac.

Based on the subdivision of a sign into three parts of 10° each. Each decan of a sign expresses subtle differences that distinguish it from the other two decans as described by its planetary sub-ruler, which operates in conjunction with the natural planetary ruler of the sign. The first decan of a sign (0° to 10°) is sub-ruled by the natural ruler of the sign; the second decan (10° to 20°) is sub-ruled by the ruler of the next sign in the zodiac that belongs to the same triplicity; the third decan (20° to 30°) is sub-ruled by the ruler of the remaining sign in that triplicity.