152 TRUB LONGITUDE OF A PLANET A rule for finding the longitudes of the Sun and the Moon at the end of the parva-tithi: 64. Multiply the unelapsed, part of the (parva) tithi or the elapsed part of the (next) tithi by the (true) daily motions of the Sun and the Moon and divide (each product) by the diffe- rence between the (true) daily motions (of the Sun and Moon). The longitudes of the Sun and the Moon increased or dimini- shed (in the two cases respectively) by the quotients (thus ob- tained) should be known as the longitudes agreeing to minutes of the Sun and Moon-the causes of the performances of the world. By the parva-tithi is meant the fifteenth tithi called purnima (i.e., full moon day) or the thirtieth tithi called amāvāsyā (i.e., new moon day). The end of the former occurs when the Sun and Moon are in opposition in longitude, and the end of the latter occurs when the Sun and Moon are in conjunction in longitude. At the time of opposition of the Sun and Moon, the longitudes of the Sun and Moon differ by six signs but otherwise agree to minuts of arc. At the time of conjunction of the Sun and Moon, the longitudes of the Sun and Moon are exactly the same and therefore agree to minutes of arc. Hence the above rule. ¹ For sunrise on the parva-tithi in the first case and for sunrise on next tithi in the second case. 2 The same rule is stated in SuSi, iv. 8; PSi, vi. 1; MSi, v. 4(ii)-5 (i); Sise, ii. 84; and Sisi, I, ii. 70; Nilakantha (TS, iv. 1-8) and Kamalā- kara (SiTV, ix. 1) have prescribed a successive repetition of the above rule. The method given in LBh, iv. 1 is approximate and simpler.
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