On the topic of Bravely Second's Astrologer, I went and found some descriptions for how the job plays in that game. While it is a different game entirely I still consider it interesting since previously the job has barely existed in the Final Fantasy series. Aside from what we've been told and a few seconds of benchmark footage with animations we can't comprehend there isn't much else to draw speculation from.

The Astrologer is another new job in Bravely Second, and it focuses on “Moon Magic” that helps the party with supports such as attack and defense increases. In the demo, they don’t learn any offensive magic, so they were used as pure buffers.
Astrologers come loaded with buffs for things like offense, defense, and elemental affinities and are also capable of raising success rates for chance-based abilities, making them another job that’s effective at lending out support during skirmishes.
It has been confirmed that Astrologian will utilize their celestial deck for the purpose of buffing the party, but to what extent has yet to be clarified. Many seem to suspect that its capabilities will exceed that of Scholar and with buffing being the primary specialization for Astrologer it's likely there will be a parallel.

I'm extremely anxious to learn more about how Astrologian will utilize their celestial deck. With it being such a supposed core aspect of the job they have hardly given us any information.