सिद्धान्तशिरोमणि: गणिताध्याय (भास्कराचार्य - ग्रहगणित, मध्यमाधिकार व स्पष्टाधिकार सटीक)

36 This has to be converted into solar days to give us the number of degrees of the error. The conversion is effected by the rule of three as “If T tithis of a Kalpa constitute S solar days of the Kalpa, what number of solar days corres- ponds to (R' × 30) / S ?” The answer is ((R' × 30) / S) × (S / T) = (R' × 30) / T = R' / (T/30) = R' / L where L is the number of lunations in a Kalpa. This R' / L being the number of solar days corresponding to the Adhimāsa-Sesha upto the day concerned, the corresponding longitude of the Sun namely R'° / L must be subtracted from the Sun’s longitude. Now the question arises whether we have to multiply this R''° / L by 13 to be subtracted from the longitude of the Moon; not necessary, enough to subtract R'° / L only, for, the Adhimāsa- sesha extends from the preceeding Amāvāsya only when the Moon’s longitude was equal to the Sun’s longitude. We have thus got the mean positions of the Sun and the Moon at the ending moment of the tithi on the previous day. To get their mean positions at the Sun-rise of the concerned day, we have to make amends for the time in between, which is no other than Avama-Sesha as a fraction of a mean solar day. Here Bhaskara makes an ingenious approximation. The maximum Avama-Sesha could be a tithi only and the Sun moves roughly by his daily mean motion during a tithi. So, the rule of three adopted is ‘If for one tithi, the Sun’s daily motion is to be reckoned, what for the Avama-Sesha? The answer is Avama-Sesha multiplied by the Sun’s daily motion. The Avama-Sesha being of the form R / T, (R / T) × m' = (R / T) × 59 (8' / 60) =