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

lagna of the moment of New Moon. Computation of the
zenith-distance of the Vitribha is a little cumbrous, so
that, for brevity, it is sought to compute the culminating
point, obtain its declination and thereby its zenith-distance
which could be taken to be the zenith-distance of the
Vitribha also, from which the Nati is calculated.
We are directed to obtain first the Nata or the hour
angle of the Sun for the moment of New Moon. We know
on that particular New Moon day how long Amāvāsya
will last after Sun-rise ie. we know when the actual
moment of New Moon occurs on that day. We also know
the duration of day time on that day so that subtracting
the time of occurence of the New Moon after Sun-rise
from half the duration of day, we obtain the hour angle of
the Sun (Nata) in nādis. Now the Moon's longitude is
effected by parallax, the effect being depression of the
Moon. It is roughly estimated that the hour angle ex-
pressed in nādis is increased by ¼ of its value on account
of this. Strictly speaking the effect of parallax is far more
on the position of the Moon than on the Sun. But the
Hindu procedure apparently treats the Sun alone for
parallax. The reason is that at the moment of geocentric
conjunction of the Sun and the Moon, when we consider
the combined effect of parallax on the Moon and the Sun
at once, for a given place, we may as well compute the
relative position of the Sun effected by parallax. Let the
hour-angle of the Sun in nādis be x. Then effected hour-
angle will be x (1 + ¼) = 5x/4 nādis. But each Rāsi being
taken roughly to rise in 5 nādis, the hour-angle in Rāsis
will be 5x/4 ÷ 5 Rāsis x/4. Hence we are directed to
divide the hour-angle of the Sun in nādis to divide by 4.
This x/4 being substracted from the longitude of the Sun,
we get the longitude of the culminating point. Then we
are directed to obtain the declination of the culminating
point from the formula H sin δ = H sin ω × H sin λ ÷ R,