History of Hindu Astronomy 2

Interpreting the Universe-2

Branches of Astronomy

The three branches of Astronomy, namely Ganit, Samhita and Hora/Jatak deal with separate subjects, though some portions may be common to some branches. With the progress of time and the updating of knowledge, some branches got merged.

The Ganit branch has three sections 

 i. Siddhant सिद्धांत 

 ii, Tantra तंत्र

 iii, Karana करण

Of the Siddhant and Tantra sections, one deals with the calculation of planets' places 

and the other primarily describes the structure of the Universe to include, knowledge of the celestial sphere, construction of instruments and units of measurement of time and other connected subjects.

The Karana deals with planetary calculations only.

Different definitions of these sections are also found in the ancient texts. The subject matter has been intermingled in it.

The Samhita branch consists of two parts. One deals with the movement of planets and their mutual conflicts, the consideration of benefic or malefic effects of comets, meteors, eclipses and omens on the world. 

The other part deals, with the selection/consideration of auspicious moments for starting events in an individual's life.

The Hora/Jatak branch, consisted of the study of the ascendant in a birth horoscope,to forecast events in life. Later it was divided into two parts. The study of ascendant was known as Jatak and the other was known as Tajik. Tajik also considered the study of events in life but from the ascendant of the annual horoscope. Tajik came into vogue around 1200 Saka/1122 CE.

The aim of our astronomy is to know the actual planetary positions. Accurate knowledge of mean motion and their position comes from accurate knowledge of the true position and motion of the planets. 

The primary subject of the mathematical branch of astronomy is to know the true position and motion of the planets.

Mean Motion. Counting the number of revolutions of a planet in a given epoch/time, and converting this revolution into, average daily motion is called the Mean motion. Panchsiddhantika पंचसिद्धांतिका has a record of such revolutions.

True Motion. The motion of planets, as observed, is not the same. Eg, Jupiter's movement varies from 1' to 15' and sometimes retrograde. This daily motion is termed as true motion and this position is found. The planet is actually found to be near or ahead of the position, calculated from its mean motion.

The history of astronomy can be ascertained from the references to astronomy in the ancient texts. to know the Mean motion and True motion of planets. 

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Reference: Bhartiya Jyotish Shastra Part I