To be honest, I'd've been more than happy with the differentials between Sharlayan and Ishgardian being Astrologist and Astrologian. But then again, you're right in that is isn't really the same in terms of translating, and you can't really use Astronomer for a number of reason. =)
Ah well, Astrologian is fine with me. I just worry that some folks are going to end up pronouncing it incorrectly for a while and others are going to shorten it (Go Astros!) Either way, nice to see you again. Get to work on the Dravanian naming and Au Ras soon, please =)
EDIT: Oh by the way, slight off-topic but I did want to ask something regarding Machinist.
In the past FF games have often used the term Machina using a hard "C" sound (Mah Kee Nah). I wonder if the pronunciation of Machinist is supposed to using a similar sounding pronunciation or if you're going for the more traditional pronunciation?