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

479 This condition is also reverse to what has been stated in the case of rising. The case of a superior planet rising in the west also never happens, because it is the Sun that overtakes the planet and also the superior planet cannot be retrograde while near the Sun. The case of rising which has already elapsed the Iṣṭa- Kālāṁśas y will be evidently greater than x ie. y > x. To obtain the time by which the rising will take place after the moment in question, ie. the rising of a superior planet which is direct and an inferior planet which is retrograde, we have to take the difference of the prescribed and Iṣṭa- Kālāṁśas and find out the time by rule of three as follows. (1) Since we have to find the corresponding arc of the ecliptic in minutes of arc, from (y - x) × 60' the difference of the Kālāṁśas of the equator converted into minutes ie. asus we have first to use the proportion. "If by the rising time of the Rāśi t in asus in which the planet is situated we have 1800' of the ecliptic, what will we have by (y - x) × 60? The answer is (y - x) × 60 × 1800 / t . Next we have to find the days when this arc of the ecliptic is covered by the proportion. "If the Sun overtakes the planet by (u - v) minutes of the ecliptic per day, how many days are taken to cover the above arc?" The answer is as stated. The answer gives in days together with fraction of a day when the planet is likely to rise. We have to repeat the process because the motions of the planet as well as the Sun differ from moment to moment and the time calcu- lated above by rule of three taking into account their motions for the entire day will be only approximate. The computation in the case of setting of a planet may be similarly considered, the setting of a superior planet in the west or that of a direct inferior planet in the east.