Decan 3 of Aquarius

This is the third ten-degree segment of Aquarius, the fixed air sign, spanning 20 to 30 degrees. Its ruler in the Chaldean order of faces is the Moon, reached by continuing the planetary sequence around the thirty-six decans. The decan is the oldest layer of astrology, the thirty-six having begun as Egyptian stars used to divide the year into ten-day weeks and the night into hours, absorbed into the Greek zodiac as ten-degree arcs only in the last centuries BCE.

The Golden Dawn of 1888 assigned the thirty-six minor arcana to the decans in zodiacal order; this segment bears the Seven of Swords, titled Futility or Unstable Effort, its Moon-in-Aquarius planet taken from the face ruler, the sevens of the mental suit and the detached air sign matching the card's image of a plan carried out by half-measures. The tarot correspondence is a modern overlay on the older decan scheme rather than anything descending from Egypt or the Hellenistic tradition.

The third decan of Aquarius runs from 20 to 30 degrees of the sign and is ruled, in the scheme this atlas records, by Moon.

The card on the decan

In the Golden Dawn's assignment this decan carries the Seven of Swords. The mapping is one to one and exhaustive: the thirty-six small cards numbered two to ten across the four suits match the thirty-six decans exactly, taken in order from the Two of Wands at the first decan of Aries. The suit follows the sign's element, so Aquarius is a Air sign and takes a card of Swords, and the rank follows the position in the sequence, which puts the seven here.

Why the rulers carry over between signs

The thirty-six rulers run in the Chaldean order, the seven planets arranged from slowest to fastest as Saturn, Jupiter, Mars, Sun, Venus, Mercury and Moon, applied one after another right round the circle beginning with Mars at the first degree of Aries. Because thirty-six is not divisible by seven, the sequence does not restart at each sign. It runs straight through the boundaries, which is why the rulers of a sign's three decans are not the sign's own planets and why the pattern only closes after the whole zodiac.

What the atlas is recording

The degrees and the ruler are the attributions this atlas holds for this decan, and the card is the Golden Dawn's. All of them are traditions with variants rather than settled facts, and the decan itself, as a ten degree segment of a sign, is the only part that is simply arithmetic.