Planetary Theories in Sanskrit Astronomical Texts

Abstract

The origin and development of planetary theories in India are still imperfectly understood. It is generally believed that fullfledged planetary theories capable of predicting the true positions of the Sun, Moon and Star-planets appeared in India along with the emergence of the siddhāntic astronomical literature. Before this siddhāntic astronomy there had existed the Vedāṅga Jyotiṣa of Lagadha, prepared around circa 400 B.C. in the Sūtra period more or less on the basis of astronomical elements developed in the time of the Saṃhitās and the Brāhmaṇas. This Jyotiṣa propounded a luni-solar calendar based on a five-year period or yuga in which the Sun made 5 complete revolutions. Moreover, this quinquennial cycle contained 67 sidereal and 62 synodic revolutions of the Moon, 1830 sāvana or civil days, 1835 sidereal days, 1800 solar days and 1860 lunar days. An important feature of the Jyotiṣa is its concept of the lunar day or tithi which is a thirtieth part of the synodic month. The tithi concept was also used in Babylonian astronomy of the Seleucid period. To trace the motion of the Sun and the Moon and to locate the positions of fullmoons and newmoons in the sky a stellar zodiac or a nakṣatra system coming down from the times of the Saṃhitās and the Brāhmaṇas was used. The Jyotiṣa was acquainted with the solstices and equinoxes, the variation in day-length of which a correct ratio was given. It is, however, silent about the inclination of the ecliptic, the non-uniform and irregular motion of the Sun and the Moon and various other important elements.