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

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cos z = sin ϕ sin δ + cos ϕ cos δ cos h
Put z = 90 + θ, h = 90 + H, δ = δ in the positions A, B
and z = 90−θ, h=90−H. δ=−δ in the positions A', B'
We have then − sin θ = sin ϕ sin δ − cos ϕ cos δ sin H
and sin θ = − sin ϕ sin δ + cos ϕ cos δ sin H
which are identical. This means that the altitude θ below
the horizon with +δ in the positions A, B is computable
with −δ in the positions A', B'. This accounts for the
statement made ‘गोलविपर्ययेण’.
The second statement of the latter half of verse (2)
says Śankutala = Śanku × ˢ/₁₂ which we have proved in
Tripraśnādhyāya.
Verse (3) and first half of (4). To obtain the Bhuja
of the Sun.
The Śankutala of the inverse altitude or the altitude
below the horizon, is north (in contradistinction to what
it is above the horizon). The sum or difference of the
Agrā and Śankutala according as they are of the same
direction or of opposite directions, is the Bhuja. The sum
or difference of the Bhujas of the Sun and Moon, according
as they are of opposite or the same directions is what is
called the Spaṣṭa Bhuja whose direction is to be construed
as that of the Moon. If the Bhuja of the Moon falls short
of that of the Sun, then the direction of the Spaṣṭa Bhuja
is that opposite to that of the Moon.
Comm. In fig. 113, we have shown five different
positions of the Sun S₁ to S₅ the feet of the Śankus being
B₁ to B. From these feet of the Śankus draw perpendiculars
on the Udayāstasutras as well as on the East-west line their
points of intersection being respectively A₁ to A₅ and
C₁ to C₅. The perpendiculars from the feet of the Śankus
on the East-west line go by the name Bhujas, the perpendi-