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

502 Verse 2. These estimates being multiplied by the difference of the radius and Śīghrakarṇa and divided by thrice the Śīghra-antyaphalajyā are to be added or sub- tracted from the mean values above given according as the Śīghrakarṇa is less or greater than the radius to give the rectified values. Three minutes of arc are to be construed as one angula in this respect. Comm. When the Śīghrakarṇa equals the radius we know that the planet is situated at the mean distance. The word planet here stands, of course, for the Mandaspaṣṭa- graha which may be roughly taken to be the mean planet, the equation of centre being small. If the Śīghrakarṇa falls short of the radius, then evidently the planet is nearer the earth than the mean position so that disc of the planet appears to be bigger. Otherwise, the planet is further and its disc appears to be smaller. It was noted that approximately there was an increase or decrease ⅓ of the magnitude of the disc by the decrease or increase of the Śīghrakarṇa by the antyaphalajyā. Hence, in between the two positions, rule of three is used to obtain the magni- tudes as follows. "If by a difference of the Śīghrakarṇa and radius equal to the antyaphalajyā, there is a difference of ⅓ of the actual magnitude, what would it be for an arbitrary difference?" The answer is d × ⅓ × 1/a = d/3a where d = Śīghrakarṇa or radius and a the antyaphalajyā. This difference is to be added or subtracted to the mean value, as the case may be. Verse 3 and first half of 4. To obtain the time of the conjunction of two planets, compute the difference of the longitudes of two planets, and divide by the difference of their daily motions. If one of the planets be retrograde, divide by the sum of the daily motions. The result gives the number of days approximately after the moment of conjunction if the slower planet has a longitude falling short of that of the quicker. If one of the planets be