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

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kamāsās do occur when the Suddhi happens to be more
than 21, but in this case one of the months prior to Bhādra-
pada happens to be an Adhikamāsa and then by the time
Kārtica is reached, the Samkramaṇa occurs not at the
beginning of Kārtica but a little later, which means that a
second Samkramaṇa could not occur before the lapse of
that lunation. This therefore will not be a Kshaya month.

The Suddhi which is defined as the number of tithis in
between a New-Moon and a Samkramaṇa, is clearly the in-
terval which has been gained by the luni-Solar system over
the Solar. This S'uddhi increases at the average rate of
11 days, 3 ghatis, 52 palas and 30 Vipalas per an year as
we have seen already. For the occurrence of an Adhika-
māsa during the course of an year the Suddhi at the begin-
ning of the year must be such that it accrues to a lunation
during the course of the year. The apogee of the Sun being
almost stationary having a very slow motion the lengths of
the Solar months do not vary appreciably for a good number
of years. Taking that the Sun's apogee is roughly at 80°
longitude (78° according to Hindu Astronomy) the Sun's
motion is less than his average from the moment when he
has 350° longitude upto the moment when he has 170°, so
that the Moon gains rapidly over him during this period.
In other words the lunations during this period are of
shorter duration i.e. the luni-Solar months of chaitra upto
Sravana will be shorter in length so that S'uddhi increases
rapidly from March upto August. Thereafter it will attain
a stationary value just for a little time and then decreases
for the next six months upto February. The increase,
however, far exceeds the decrease and the balance of in-
crease per year is as mentioned above is 11-3-52-30.

Bhāskara mentions in the course of the commentary
that (1) the average length of a lunation is 29 days, 31
ghatis and 50 palas; (2) the average length of a Solar
month is 30-26-17 ; (3) when the daily motion of the Sun
happens to be 61', then the Solar month will have a length