Decan 1 of Gemini

This is the first ten-degree segment of Gemini, the mutable air sign, spanning 0 to 10 degrees. Its ruler in the Chaldean order of faces is Jupiter, reached by continuing the sequence of the seven planets around the wheel of thirty-six decans. The decans are the most ancient stratum of the tradition, beginning as Egyptian stars whose risings marked the ten-day weeks of the year and were absorbed into the Greek zodiac as ten-degree subdivisions 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 Eight of Swords, titled Interference or Shortened Force, its Jupiter-in-Gemini planet taken from the face ruler, Jupiter in its detriment here, which suits the card's theme of restriction. The tarot correspondence is a modern overlay laid over the far older decan scheme, not part of the Egyptian or Hellenistic material.

The first decan of Gemini runs from 0 to 10 degrees of the sign and is ruled, in the scheme this atlas records, by Jupiter.

The card on the decan

In the Golden Dawn's assignment this decan carries the Eight 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 Gemini is a Air sign and takes a card of Swords, and the rank follows the position in the sequence, which puts the eight here.

Two ruler schemes, and which one this is

Two schemes for decan rulership are in circulation and they disagree. The one recorded here runs the seven planets in Chaldean order continuously round the circle. The other, the triplicity scheme, gives a sign's three decans to the rulers of the three signs of its own element in order, so the rulers stay inside the element and restart at every sign. Both are attested in the tradition, neither is a corruption of the other, and a reader comparing two books will find them differing here without either being wrong.

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.