In the Brahmasphuta-siddhanta

How can the commencement of the planetary cycles be logically consistent? Bhaskaracharya also states in the Siddhanta-shiromani, "From the rising of the Sun in the city of Lanka, the first day of his week began," which is in agreement with what was stated by Brahmagupta. || 4 ||

V. Bha. Commentary by Vishvanatha Jha: Now, in this science, the knowledge of all useful subjects such as the planets and stars is obtained only in relation to the Earth. Therefore, there is a deliberation to determine what its shape is and what its dimensions are. In a certain place, on level ground devoid of trees and such, someone saw at night a lit lead-pot-lamp atop a brick pillar standing at some distance. Wondering "What is this?", he approached it. Having gone near and seeing another lamp at the base of the pillar, he was astonished: "Even though there was no obstruction to my vision, why was the lower lamp not seen from a distance?" He inferred that the obstruction to his vision was the Earth itself; thus, it is proven that there is curvature on the surface of the Earth.

Furthermore, even while at the top of a tree, I observe a single ripe fruit falling in many places on the ground in all four directions; from this, it is inferred that there is an attractive force akarshana-shaktigravitational force in all points residing on the Earth's surface. Likewise, by measurement, it is determined that the string measuring the distance from the treetop to the point of falling is shorter than the strings tied to points other than the point of falling. From seeing this natural property of a sphere—that the external segment of a line from a point outside to the surface is smaller than the external segments of other lines—the idea arose that there is a certain sphericity. Therefore, having first hypothesized that sphericity, a test is made as to whether spherical properties exist here or not.

By the power of imagination, a line is conceived passing through the center of the Earth. Since the same effect is produced by imagining the attractive force at the center of the Earth and at the surface points, it is hypothesized that this force is greatest at the very center of the Earth. A wise man certainly performs a task through many servants only if it cannot be done by one. Therefore, the wise Creator Brahma, for the task of attracting objects, surely passed over the surface points as "servants" and appointed the single central point of the Earth as the "servant" the primary source of gravity.

Having erected two equal pillars at two places on the Earth, and having sighted the top of the second pillar from both the top and the base of the first pillar, a triangle is formed. By knowing the angle of vision and the segment of the pillar within it, and by the ratio of the angles, one knows the distance between the tops of the pillars. Then: 180° — (2 $\times$ the angle at the top of the pillar) = the angle at the center of the Earth produced by the two extended pillars, because the said triangle is isosceles. Then, by the ratio of the angles:

There are other subjects as well.

Now, having known the difference between two equatorial coordinates and two declinations, one calculates the maximum declination obliquity of the ecliptic to find the desired declination.

This calculation was performed through observation by modern scholars with extraordinary intellect via sea voyages and the like; that has been included in the Siddhanta-Setu. Then, from the (Known Side — Pillar Height) = Earth's Radius; having done this...