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