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

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d = a Sin θ / (Sin Z - (Sin θ)). Strictly speaking d / Sin θ = a / Sin (Z - θ)
so that d = a Sin θ / Sin (Z - θ). Since (Sin Z - Sin θ) < Sin (Z - θ)
∴ the estimate of d obtained is a little greater than its
true value. We shall discuss other possible methods of
finding the Moon's distance in the chapter on lunar eclipses.
Having got the distance of the Moon as afore-said,
it was easy to obtain the angle ∝ marked in fig. 1 for,
Sin ∝ = M₁ M¹ / O M¹ = a / d = 2πa / 2πd = 4967 / 324000
Since ∝ is small Sin ∝ = ∝ radians.
∴ ∝ = (4967 × 3438) / 324000 = (4967 × 191) / 18000 = 52.7'
Since the Moon's daily average motion 790' — 35" is had
in sixty Nadis, 52.7' of motion is covered in (52.7 × 60) / 790.5
approximately = 60 / 15 = 4 Nadis. Thus the fact that we are
given the horizontal parallax as 4 Nadis in the context of
lunar eclipses is based on this.
Having obtained thus the distance of the Moon from
the centre of the earth E, and having measured the angular
diameter of the Moon's disc with the help of the protractor
mentioned above, from the triangle EAM (Ref. fig. 2) where
[चित्र: Fig. 2 - त्रिभुज EAM जिसमें E पर कोण β, भुजा EM = d, बिन्दु M चन्द्रमा का केन्द्र, AM = r' त्रिज्या, और स्पर्शरेखा EA है।]
Fig. 2