So, I was reading the Encyclopedia and it provides an amazing source of material for divinatory magick when possibly roleplaying an AST.

But then, I come to the question on how to actually roleplay an Astrologian when it comes to adventuring and more specifically combat?

The other spellcasters are bound to shape their aether (or the surrounding's) into destructive elemental magicks, or healing ones...

But when it comes to AST, how, let's say, the malefic spell can be represented?

It is a star cluster conjured by attuning your own aether to the constellation? How the cards get into this mix? ... Or it would be you inducing a "malefic" fate to your foe using a drawn card, so it would, for example, trip and break their neck when trying to hit you?

The game itself represents it by simply conjuring stars and such, but the lore never makes it very clear on how it happens.