once krishna said

triskandam jyotisham hora ganitam samhetate cha | eteshwapi trishu shrestha horeti shruyate mune || (1.3 BPHS) Jyotisha is divided into three parts hora ,ganita and samhita hora means the predictive methodology ganita means the mathematical formulas samhita means the collection of various rules and formulas which also contains details like science of palmistry , omens , clairvoyence , remedies and rituals (karma kanda) Because of computer softwares the ganita part has been sidelined and hora part is been practiced mostly. the pillars of astrology 1.signs (Rashi) 2.heavenly bodies(graha) 3. bhavas (houses)  4. upagrahas (non luminious planets) 5. Yogas  6. nakshatras 7.Dashas The earth and the other planets revolve around sun through a certain path in heavens. This path is referred as ecliptic. On both sides of the ecliptic there is an imaginary belt of 9-9 inside which all these grahas revolve. This broad belt of 18 is called as zodiac. To facilitate the study each zodiac is divided in