I don't entirely feel comfortable in saying Astrologian has good single target DPS as compared to a White Mage, but I would say that their aoe is pretty good. Here's how:
(Diurnal Sect)
If you really wanted to go all out on AOE dps, and the tank does a big pull, what you do is wait for the tank to put them in position, Synastry (Bll if need be) and cast Aspected Helios, followed by CU, and then followed by Aspected Benefict. After which use time dialation to increase their HOTS to around 30s (Before CU and AB ware off)

And at this time your tank should have a super potent regen tick, that should heal for almost as much as a regular B1.
Then at this point cast Light speed
Followed by Luminous Aether
And finally followed by Celestial Opposition

Cleric Stance
Start the gravity spam
You shouldn't even have to get out of Cleric Stance to heal, since the regen will be THAT potent.

????
Profit.
Your welcome