150 TRUB LONGITUDE OF A PLANET "sighrantyajiva etc.". This (sum or difference) is the true daily motion (of Venus or Mercury). Thus has been stated the difference of procedure (in the case of the superior and inferior planets). The daily motion thus obtained is always very nearly equal to the true daily motion and should be made use of in practical calculations. The above rules relate to the determination of the true daily motion of the planets, Mars, Mercury, Jupiter, Venus, and Saturn, and seem to have been inspired by the rule of Aryabhata I's midnight day-reckoning which has been adopted by Brahmagupta in his Khanda-khadyaka. They are different from the analogous rules found in the other works on Hindu astronomy. ³ They have been derived by taking the difference between the longi- tudes of the planets for two consecutive days as in the case of the Sun and Moon. The rules differ in the case of superior and inferior planets be- cause the methods of finding the true longitudes in the two cases differ. The daily motion obtained by the application of the above rules is known as jivabhukti as in the case of the Sun and Moon. It is probably ¹ That is to say: Multiply the mean daily motion by the current Rsine- difference corresponding to the mandakendra determined from the correct- ed mandocca (see stanza 53) and also by the corrected manda epicycle and divide the product by 18000: the result is the mandakendrajyagati- phala. Add it to or subtract it from the mean daily motion of the planet (as necessary). Subtract the sum or difference thus obtained from the daily motion of the sighrocca. Multiply the difference by the current Rsine- difference corresponding to the sighrakendra and also by the corrected sighra epicycle and divide the product by 18000. Multiply that by the radius and divide by the sighrakarna, and reduce that to the correspond- ing arc. Add it to or subtract it from the mean daily motion already. corrected for the mandakendrajyagatiphala. 2 See KK (Sengupta), ii. 19; KK (Babua Misra), ii. 26. Also see Pṛthua daka's comm, on this stanza. 3 e. g. by Lalla, SiDVṛ, I, ii. 40.
- See supra stanzas 14-17.
