Jyotihshastra: Astral and Mathematical Literature c4.s4.5

c4.s4.5

Planetary tables in India can be classified into three categories. "Mean linear" arrangements tabulate the increments in the mean longitudes of the planets in successively smaller units of time; the *manda* and *śīghra* equations are tabulated separately. This is the form of planetary table employed by Ptolemy and by most of his eastern and western successors. The "true linear" arrangement tabulates the true longitudes of the planets in ideal years at given intervals (*avadhis*). The ideal years assume initial mean longitudes of the planet at equal distances around the zodiac while the initial mean longitude of the Sun is always at Aries 0°; the intervals between the initial mean longitudes that are attested are 3°, 6°, 12°, 13;20° (a *nakṣatra*), and 30°. Mean motion tables in terms of these intervals allow one to locate the planet within this system for any given year. The *avadhis* are normally periods of fourteen days. The "true linear" arrangement seems to be an Indian invention. Finally, the "cyclic" arrangement utilizes the Babylonian goal-year periods (that of Venus is changed from 8 to 227 years). The planet's true longitude for the beginning of each *avadhi* in each year of its goal-year period is entered in the table; after one period the cycle is repeated. The goal-year periods themselves were introduced into Indian astronomy from Islamic in the early seventeenth century;¹⁷³ the "cyclic" tables produced in that century and the succeeding two in West and Northwest India combined these goal-year periods with the native tradition of true linear tables.