It's also worth mentioning that stars in this fantasy universe are not necessarily the same as stars in ours. They don't have to be impossibly distant suns - they might actually be quite close by, not much further away than the sun or moon (which, in turn, may ALSO be a similar distance from the planet, with the sun being much smaller and closer than the sun in the real world). While Occam's Razor postulates that we should assume that the universe there works like the one here, unless directly contradicted, we do need to remember that this is a fictional universe, and the crazy claims made by the natives may be actual truth, rather than unenlightened nonsense.

That said, it's clear that the Astrologians are not infallible. Like most, they thought that Dalamud was a true moon and plotted their astrology accordingly - up to the point when it was called down and Bahamut broke free. Even afterwards, though, they continue to perform their astrology assigning importance to the empty place Dalamud used to be.

Or is this, in fact, a mistake at all? In this world, it could be the case that whether an astral body is artificial or not does not change the fact that it is an astral body, and therefore has influence on fate? It's interesting to think about - particularly if the world ever returns to the level of advancement enjoyed by the Allagans. Astrology could become pretty key if affecting future events could be achieved simply by launching satellites into proper positions in the sky! "Huh, so, you next Watersday to be sunny? We're gonna need new moons here and here, stars in these four positions, and move Moon #728 from this position to here. The engineers are gonna need to work overtime, but I think we can get this done!"