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

PARVASAMBHAVĀDHIKĀRA
Investigation into the occurence of an eclipse
Verses 1–2. Multiply the number of years that have
elapsed from the beginning of the Kaliyuga by twelve and
add the number of months elapsed from the beginning of
the luni-solar year. Let the result be x. Then add
[2 x (1 - 1/898)] / 65 to x. Let the result by y. Then the longi-
tude of what is called Sapāta-Sūrya or the longitude of the
Sun with respect to a node will be x Rasis +
[(2 y + 503) (1 + 1/169)] / (3 × 30) Rasis. If this longitude be less
than 14°, then a lunar eclipse is likely to occur.
Comm. The first operation indicated above in direct-
ing x to be added to [2 x (1 - 1/898)] / 65 is intended to obtain the
lunations that have elapsed from the beginning of the
Kaliyuga. In this behalf we are asked to multiply the
elapsed years by twelve to get the number of solar months.
Here there is one subtlety to be noticed. The years that
have elapsed are not entirely solar. In fact the years
reckoned according to the luni-solar system were all
originally luni-solar; but according to the convention of
intercalary months, they were rendered solar upto the
point of the latest intercalation, for, solar months plus
intercalary months are equal to the elapsed lunations.
From the moment of the end of the latest intercalary
month, the subsequent years or year or fraction thereof
would be luni-solar only. Nonetheless, no difference will
be there in the computed Adhikamāsas in adding a few
lunar months to the solar and taking them all to be solar.
The maximum error committed in so doing will be of
the order of (no. of days in a solar month minus no.