Principle purpose of this lecture is to present on Theoretical Explanation: Solar System. Ptolemy explain the geocentric model, that the Earth is at rest at the center of the Universe. Copernicus published the heliocentric model. Galileo explain his observations by telescope verified the heliocentric model. Kepler deduced empirical laws of planetary motion from Tycho’s observations of planetary positions. And Newton developed the full theory of planetary orbits.