ब्राह्मस्फुटसिद्धान्त (ब्रह्मगुप्त - शून्य, कुट्टक, बीजगणित एवं सम्पूर्ण २१ अध्याय सान्वय सटीक)

CHAPTER VII Epicyclic Theory of Ancient Indians We shall give here some details of the Indian concepts regarding the motion of planets or wandering bodies among the stars. The Vedāṅga Jyotiṣa (1400 B. C. or earlier) does not speak of this, A comparison of the astronomical constants of the Greek and the ancient Indian systems, points unmistakably to the conclusion that the Indian constants as determined by Āryabhaṭa I and his successors, are almost in all cases different from those of Greeks. Indian astronomers were highly original in their con- cepts and treatment. The originality of Āryabhaṭa I and other astronomers would be seen from what we are discribing below. Apparent Motions of the Sun and Moon We have the following passages from Āryabhaṭa : All planets move in eccentrics to their orbits at the mean rates of angular motion, in the direction of the signs of the zodiac from their apogees (or aphelia) and in the opposite directions from their Śīghroccas. The eccentric circles of planets are equal to their concentrics and the centre of the eccentric is removed from the centre of the Earth. The distance between the centre of the Earth and the centre of the eccentric is equal to the radius of the planet's epicycle; on the circumference (whether of the epicycle or of the eccentric) the planet undoubtedly moves with the mean motion. Here the central idea was that undou- btedly planets moved unifomly in circles round the Earth; if the motion appeared to be variable, it was due to the fact that the centres of such circle (i. e. the con- centric circles) did not coincide with the centre of the Earth. Fig. 15