Rajesh Kochhar
The oldest astronomical text in India is Vedanga Jyotisha, which is a part of the Vedic corpus. Its oldest parts could be as old as 1400 BCE. Asoka’s Edicts (3rd cent BCE) are consistent with Vedanga Jyotisha. A feature of this period is the identification of planetary positions with the help of nakshatras. In the centuries following Alexander, Greco-Baylonian inputs were received into India from the northwest which revitalized Indian mathematical astronomy, seen in fully blown form in Aryabhatiyam (499 CE). These inputs include (i) accurate luni-aolar calenndar (the Vikrami or the old Shaka, calendar), (ii) 12 rashis, and (iii) week days. Aryabhata { note the single t} introduced for the first time, in the Indian context, mathematical theory of eclipse which tells you that eclipses take place when the Moon is at one of the two nodes. Aryabhata’s contemporay, Varahamihira, designated these nodes as shadow planets and named them Rahu and Ketu. This is the beginning of the nava graha concept. I do not think it would have been possible to cast a horoscope according to Vedanha Jyotisha. Present-day astrology and ritual of which the accurate calendar, week days and rashis are integral part is post-Vedic and not Vedic.