Hellenistic extends from the period after Alexander the Great until the predomination of christianity (around the "6th cent bce"). I wrote Hellenic, not Hellenistic.
What exactly is divination anyway? I know of Mancery (oracle of Delphi, of Dodone) of necyomancy, of dream-mancery and of the therapeutic temples of Asclepius where a special kind of Mancery was practised. Plato in Phaedrus analyzes what Mancery is about. Now, of divination I do not know about. Can you help me?
Now, modern "astrology" has little relevance with actual Astrology. The definitions have been mixed and there is a transfer of properties from planets to topoi (who usually are wrongly called houses), from planets to zodia, from zodia to planets and topic and gods know what else. But in actual Astrology there are strict limits on all these three concepts (zodion, topos, planet) and a specific rational behind each, which is totally missing today. Not to mention that it is completely desynched from actual stellar positions. Which is unthinkable in Astrology. What is the point of studying the influences of planets, stars, constellations etc if one takes imaginary position? There is no point, no logic in that.
I recommen this article for an intro in Astrology:
http://www.projecthindsight.com/fate.htm