- Also known as 'decans'; divisions of the signs into 10° sections, each of which is governed by one of the planets. These appear to be based upon the Egyptian division of the year into 36 ten-day periods, each presided over by a particular stellar deity. The 4th century astrologer Firmicus Maternus is among many who placed great emphasis on their use, saying that a planet in its own decan is as good as in its own sign. Like Manilius before him, he attributed decan rulership to the signs of the zodiac, but most authors, including Ptolemy, gave them to the planets in descending order towards the earth, (i.e., Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon). Their order reflects planetary rulership over the days of the week.
For information and resources on the use of planetary dignities and debilities see: