The Vedic Navagraha Mantras have been compiled mainly from Rig Veda , Atharva Veda and Sukla Yajur Veda .
Jyotisha , one of the six VedAngas, deals mainly with astronomical aspects and is known as the eye of the Vedas. Jyotisha SamhitAs have been composed by Garga, NArada and ParASara. Lord SUrya has composed "SUrya siddhAntam" and taught it to Maya. The works by others include VarAhamihira, Arya Bhatta and BhAskarAcArya. This Science is used to primarily determine the planetary position and fixing auspicious times for performance of Vedic Sacrifices.
In my limited understanding, astrological predictions based on horoscope could have started at a later period.