Jyotihshastra: Astral and Mathematical Literature c4.34

c4.34

By the early fifth century when the Brāhmapakṣa began there had been introduced into India a more sophisticated form of Greek astronomy characterized by planetary models comprising the combination of an eccentric deferent with an epicycle (but without Ptolemy’s equant or special model for Mercury), or a Peripatetic model with two independent epicycles whose centers are carried by a concentric deferent,¹⁵ or one in which each inequality is accounted for by a concentric circle with an equant.¹⁶ The inequalities in the motions of the Sun and the Moon are computed by means of an eccentric, a concentric deferent with an epicycle (the preferred model), or a concentric circle with an equant; in the earlier part of the Greek period Ptolemy’s second lunar inequality was not known, though it was introduced into India from Islamic sources in the tenth century.