Indian astrology comprises three main parts viz. Siddhaanta Skandham, Samhitaa Skandham and Horaa Skandham.
(i) Siddhaanta Skandham : It deals with different time-scales ranging from a nano second to billions of years, various types of years, planetary movements, locational variations in the timing of sunrise and sunset, planetary orbits, their revolutions, cosmic distances, atronomical calculations and the geometrical methodology applied thereto as also the manufacturing of the mechanical tools for calculating time.
Again, three types of Siddhaantic treatises are in vogue. 1. Siddhaanta texts 2. Tantra texts 3. Karana texts. Of these, the Siddhaanta texts undertake time calculations since the commencement of the Kalpa. The Tantra texts reckon from the beginning of the Kali era, while the Karana texts do it from the beginning of the Vikrama Saka.
(ii) Samhitaa Skandham : Samhitaa means a compendium of various tidbits of knowledge. Its once-constituent parts had, in later times, assumed significance in their own right as absolutely independent branches of knowledge. Of them, the well-known are 1. Vaastu 2. Muhoortam 3. Gochaaram 4. Vaataavaranam 5. Bhoo-garbha-saastram 6. Saamudrikam.
Vaastu is multifarious being divided into Gruha Vaastu, Aalaya Vaastu, Silpa Vaastu and Yantra Vaastu.
Muhoorta Bhaagam explains the ways to fix auspicious timings for certain occasions like house warming, wedding etc.
Gochaaram is twofold, namely 1. Vyakti Gochaaram 2. Desa Gochaaram which is also known as Medini Jyotisham. It indicates the results of the current planetary transits.
Things like like prospecting water, detecting metals and minerals in the earth, knowing the rainfall beforehand in a given area, ways of cultivation and gemology were explained in the VaataavaraNa and Bhoo-garbha parts.
(iii) Horaa Skandham : Horaa Skandham is the most renowned and extremely popular branch of astrology, being capable of predicting the future of individuals based on the planetary position in their horoscopes at the time of their birth. For the pupose of this kind of prediction, the planetary position manifest in the birth charts is considered to be frozen for life.
Indian astrology predicts individuals' future based on the principles enunciated by any of the three schools namely, 1. The Paraasara School 2. The Yavana School 3. The Jaimini School. Of these, the Paraasara school is more popular among the Indian astrologers than any other.