The 12 division based Rashi system is believed to be an import from outside of India a couple of thousand years before while Vedic astronomy and astrology developed on 27 divisions of 13.33 degree each ( called Nakshatra ) much more earlier and it is mentioned in Vedas and Puranas . This is the angle which Moon covers from Sunrise to next Sunrise encircling Earth .
Nakshatra ( Instead of Rashi) Used for Prediction
Original Vedic Astrology is based on use of Nakshatra , also called Nadi Astrology . In this system , these Nakshatra are arranged in various ways to predict a particular outcome . These are called as Chakras .
For example , following is the arrangement of Nakshatra in Shoola Chakra ( using 28 Nakshatra ) , which predicts bad events like death / disease .
Each subject of prediction required a special chakra and there was no general method of predicting as happens in Rashi Kundali system .
Nakshatra for Calculating Dasha Period
The most common use , specific to Vedic astrology is to calculate Mahadasha or major and sub-period using Moon’s Nakshatra at birth . Unlike 12 Rashi system , 27 Nakshatra are uniformly owned by 9 planets ( 3 each ) including Rahu and Ketu , which do not own any Zodiac Rashi .
Current popular system of prediction uses 12 Rashis , 9 planets with 27 Nakshatras for Dasha calculations , as described in Brihat Parashar Hora Shashtra ( BPHS ).
Some astrologers try to mix up Rashi prediction with Nakshtra prediction but they are quite different from each other . Very few ( traditional astrologers) know predicting exclusively through Nakshatras , using Chakras and Nadi astrology . It is more accurate but complicated also . KP system of astrology is hybrid of Rashi and Nakshatra system