[Pramāṇa](https://indike.org/pramana/) › [Studies](https://indike.org/pramana/ins) › [Science, technology and education](https://indike.org/pramana/ins.science) › [Jyotihshastra: Astral and Mathematical Literature](https://indike.org/pramana/ins.science.pingree-1981) › c4.37 # Jyotihshastra: Astral and Mathematical Literature c4.37 Jyotiḥśāstra: Astral and Mathematical Literature c4.37 - **Language:** English ### [c4.37](https://indike.org/pramana/ins.science.pingree-1981.c4.37) As these geometric models of planetary motion based on the idea of the circularity of their orbits were introduced into India, it became necessary to modify the traditional Indian cosmology as expressed in the Purāṇas and other texts. This was done by transforming the disc of Jambūdvīpa into a sphere and Meru into the terrestrial North Pole; along the equator at 90° distance from each other lie Laṅkā on the prime meridian, Romakaviṣaya, Siddhapura, and Yamakoṭi; opposite Meru at the South Pole is Vaḍavāmukha. The axis of the universe passes through Meru and Vaḍavāmukha and the poles of the spheres of the planets and of the nakṣatras; the spheres of the planets rotate from West to East at a uniform velocity, driven by bonds of wind, while they and the sphere of the nakṣatras rotate diurnally from East to West. The deviations of the planets from their mean motions are caused by demons stationed at their manda (accounting for the equation of the center) and śīghra (accounting for the equation of the anomaly) uccas pulling them towards themselves by cords of wind. The relative distance of each planet’s sphere from the center of the system—that is, the center of the earth—can be computed by comparing their sidereal periods since they move equal spatial distances (but unequal angular distances) in equal times. Absolute values for planetary distances depend on the assumption of an arbitrary number of yojanas in the orbit of one of them (that of the Moon was normally chosen). In order to retain the Greek order of the planets in which the Sun is further distant from the earth than Venus, the Indians operated with the motion of Venus’ (and then, by analogy, Mercury’s) śīghra; in Ptolemaic terms the śīghra for an inferior planet is the sum of its (i.e., the Sun’s) mean motion and its anomalistic motion. - [Previous: c4.36](https://indike.org/pramana/ins.science.pingree-1981.c4.36) - [Next: c4.38](https://indike.org/pramana/ins.science.pingree-1981.c4.38) - [Up: c4](https://indike.org/pramana/ins.science.pingree-1981.c4) --- Source: [https://indike.org/pramana/ins.science.pingree-1981.c4.37](https://indike.org/pramana/ins.science.pingree-1981.c4.37) · Pramāṇa