Earth and Celestial Spheres

Abstract

The chapter commences with a discussion on the three spheres, (i) Bhūgola — the terrestrial sphere, (ii) Vāyugola — the equatorial celestial sphere (described with reference to the celestial equator which is revolving uniformly due to Pravaha-vāyu) and (iii) Bhagola — the zodiacal celestial sphere (described with reference to the ecliptic). This is followed by a discussion on the motion of equinoxes. Then, we find the description of some of the important great circles and their secondaries, which are used as the reference circles for describing the location of a celestial object using different co-ordinates. Finally, there is an elaborate discussion on the determination of the declination of a celestial object with latitude.