I still don't get how Ishgardian astrology was supposed to work

[Cleretic]

Both Ishgardian and Sharlayan forms of astrology are essentially real-world forms of divination being elevated to the point of legitimacy through magic. It's just that while Sharlayan astrology is formed of more personal fortunes and so has healing components to it to boot, Ishgardian astrology is aiming much broader, using the stars to make greater predictions about the future.

Essentially, Sharlayan astrology is a direct fortune telling (hence why its main job mechanic is a tarot spread), Ishgardian astrology is horoscopes. And Far Eastern geomancy is Feng Shui.

That said, I think we're generally meant to believe that all three of them work, it's just that in the case of Ishgardian astrology, there is a marked difference between 'works' and 'useful'.

[Kakurady]

Ishgardian astrology is aiming much broader, using the stars to make greater predictions about the future.

Essentially, Sharlayan astrology is a direct fortune telling (hence why its main job mechanic is a tarot spread), Ishgardian astrology is horoscopes.

No magick or fortune-telling needs to be involved in Ishgardian astrology - it is closer to what we would call astronomy.

Guillestet: Since the discovery by Adaunel the Younger that the Dravanian Horde were using the relative position of a celestial body we now refer to as the dragon star to determine their attacks on the Holy See, we have ever been seeking to decipher the dragons' code. Theories constructed here are subsequently taken south to the Observatorium where they are put into practice.

In other words, the dragons have been using the star as a semaphore, and by extrapolating the path of celestial objects, Ishgardians attempt to predict their attack schedule.

But the word astronomy is unknown to Eorzeans; they use astrology to describe both the Ishgardian and the Sharlayan school.

That, of course, still leaves many gaps in the lore for fans to fill. The description certainly doesn't completely preclude Ishgardian astrology from using magicks or fotune-telling. Another open gap is, what is the position relative to?


(P.S. and if you're writing fanfiction, you can totally rule that the Dravanians also use the light/aether of the dragon star to coordinate attacks. That could explain how Ishgardian predictions are not always accurate.)