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