Quote Originally Posted by Khalithar View Post
The Astrologian magic is referred to as Astromancy, Astromancy started out being practiced by the Sharlayans. They draw their power from the stars and constellations (the six cards AST uses are named after those constellations) and there is also a 7th constellation that the Astrologians only see at the moment of their death and no living Astrologian is able to connect with it until that moment.
There's also vague indications that this is just what they think they're doing but something else is going on; it's specifically mentioned by Levela that they're still using Dalamud's motion through the heavens in their readings, despite Dalamud having crashed to the ground five years and and never actually having been a moon to begin with.

It could be that Eorzea's "Belief Makes it Real" problem extends far, far beyond just the Primals.