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

47 Fig. 1 ved from a place A on the primary meridian going through Lanka, Ujjain, Kerukshetra etc by an instrumeut (A pro- tractor) described by Bhaskara under verse 5 Chandragraha- ṇādhikāra, grahagaṇita at the time of transitting. Let B be a sublunar point on the earth at the moment of that obser- vation, where B is also on the same primary meridian. Since both the places happen to be on the primary meridian, and such places were primarily known, both the observa- tions could be made simultaneously. Knowing the distance A B between the two places, the angle θ subtended by A B could be easily got from the triangle A O M where O is the earth's centre and M the Moon. As a first approximation, d / Sin θ = (d + a) / Sin Z = a / (Sin Z − Sin θ) taking O M roughly to be equal to (a + d). In the above equation, a being known