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

498
It is interesting to note Bhāskara waxing poetic in
the course of the commentary under these verses describing
how the illumination of the Moon's disc by the rays of
the Sun is effected. The description is quite apt, inter-
esting and scientific reminding us of Varāhamihirācārya's
description in the verse 'सलिलमये शशिनि etc.' in Bṛhat-
Saṁhitā. Of course, following Varāhamihira Bhāskara
also takes the Moon's globe to contain water within its
bosom which Modern Science has yet to confirm.
Verses 10, 11, 12. The Koti and Karṇa defined by
Brahmagupta, do not lead us to accordance between
computation and observation to locate the cusps. I
request good mathematicians to verify this carefully. In
a place where the latitude is (90—ω) = (90—24) = 66°,
when the ecliptic coincides with the horizon, and
when the Sun is in the beginning of Meṣa which is
then rising in the east, and the Moon in the beginning
of Makara, then the Moon is dichotomized by the
meridian and the illuminated part of the Moon's disc is
towards the east. This does not hold good according to
Brahmagupta's definition of Koti, because then the Bhuja
as well as Koti according to his definition is equal to R.
When the Bhuja is zero, the cusps will be horizontal, and
when the Koti is zero, they will be vertical. Brahma-
gupta's Bhuja and Koti both being equal to R, the cusps
therefore cannot be vertical which is against truth as
stated above. Why should I make this statement? May
my homage be to those great.
Comm. When the latitude of a place be 90—ω, and
when the ecliptic coincides with the horizon, it is clear
that in whatever positions be the Sun and the Moon
(assuming that the Moon is also approximately on the
horizon) the cusps of the Moon are always vertical, there
being Bhuja only and no Koti. But according to Brahma-