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

376 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