The Second Decan of Aquarius

This is the second ten-degree segment of Aquarius, the fixed air sign, spanning 10 to 20 degrees. Its ruler in the Chaldean order of faces is Mercury, following the continuous sequence of the seven planets around the thirty-six decans. Historically the decan is the most ancient layer of the tradition: the thirty-six were Egyptian star groups, a calendar and a night-clock older than the zodiac, folded into the twelve signs three to a sign only after Babylonian astrology reached Egypt.

The Golden Dawn, from 1888, mapped the numbered minor cards onto the decans; this segment carries the Six of Swords, to which they gave the title Science or Earned Success, its Mercury-in-Aquarius attribution taken from the face ruler, Mercury in the airy sign of the mind matching the card's theme of hard-won clarity and passage to calmer water. That tarot layer is a modern Western construction over the ancient decan scheme rather than part of the inherited astronomy.