When we look up at the heavens on a clear night, we find a multitude of celestial bodies, illuminating the sky with their radiance. It looks like a large hollow hemisphere, with the observer at the center. The planets and the luminaries seem to be scattered thorough the heavens at large distances.
This picture of the observer, the sky as a large crystalline hemisphere , is a very convenient model for the study of the Heavens.
This hemispherical model of the heavens is called Khagola, the Celestial Sphere. Another geocentric model, the Khagola is an imaginary sphere of large radius.
Astronomy, Maths and Astrology ( Siddhanta, Samhita and Hora ) are considered to be Apaurusheya, divine in origin. They were revealed to the Rishies in higher states of Consciousness and hence are revealed sciences. Descendit e Caelo, they cometh from Heaven !
Their date of compilation is believed to be 12th century BCE
Rotation, Revolution & Diurnal Motion
The earth rotates about its own axis, from west to east in the course of a day. Due to this rotation, the observer is carried eastward. But the observer is unaware of his motion in space. To the observer, the Celestial Sphere with all the heavenly bodies, is seen as rotating from east to west. This apparent westward motion of the heavenly objects is known as the diurnal motion.