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

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Sin 90 ∓ α / Sin (90 - β) = sin θ / sin ω = sin (90 - λ) / sin (90 - δ)
∴ Sin θ = (sin ω cos λ) / cos δ or (sin ω cos α) / cos β I
[Fig. 79] Similarly from fig. 79, where
P = celestial pole, N = North-
point, M = centre of the Moon's
disc, Q = latitude of the place,
h = hour-angle of the Moon,
ξ = Āksha Valana and z = Arc
of the prime-vertical inter-
cepted between the zenith
and the foot of the secondary
to the prime-vertical drawn
through M, which arc goes by
the name Sama-Vṛitta-Natāṃ,
sa or zenith-distance measured along the prime-vertical-
μ = distance of M from the prime-vertical measured along
the above secondary,
Sin ξ / Sin φ = sin (180 - h) / sin (90 - μ) = sin z / sin (90 - δ)
Sin ξ = (sin φ sin h) / cos μ = (sin φ sin z) / cos δ II
In fig. 80, where (M) is the Moon's disc, AB, the
diameter of the disc extending along the ecliptic (assuming
the Moon's centre almost on the ecliptic, which is the
case at the time of an eclipse), K, P, N respectively the
pole of the ecliptic, the celestial pole and the north point
and θ, ξ the Āyana and Ākṣa Valanas defined above, the
eclipse starts at A, the eastern side of AB, called the
Krānti-Vṛitta-Prāchī, AB being perpendicular to EF a
diameter of the disc secondary to the ecliptic. An observer
with his physical eye construes the diameter CD, which
is secondary to the prime-vertical as indicating north and
south. Naturally therefore, it is required to specify the