Answer to Question 78

Planetary Motion

Since, long, scientists have been trying to know the

Heliocentric Solar system

universe around them. They have taken great interest in the motion of heavenly bodies like sun, planets, moon etc. Ptolemy, a Greek astronomer proposed theory regarding the planetary motion. His theory was called Geocentric Theory of Planetary Motion. According to this theory, all the heavenly bodies like sun, stars, planets, moon etc. are moving around the earth, which is stationary and is taken as the centre of the universe. Copernicus challenged this theory.

In 498 A.D. a great Indian mathematician and astronomer,Arya-Bhatta, from his observations concluded that the various facts (like solar eclipse, moon eclipse, formation of day and night etc.) could be very easily explained by considering that earth revolves round the sun and also rotates on its own axis. However, due to lack of communication, his ideas could not be communicated to the western philosophers.

Geocentric Solar system

In 1543, Copernicus suggested that description of motion of heavenly bodies becomes very simple and more properly explained if we assume that sun is stationary and earth as well as other planets is revolving around it. This theory was called Heliocentric theory. Galileo later on supported this theory from his experimental study on moon and other planets.

We will now see the various constituents of the universe.