<h3>how the discovery of gravity by Isaac Newton has changed the whole idea about Earth and the planets.</h3>
Explanation:
The idea of the whole text is to let the readers understand how the discovery of gravity by Isaac Newton has changed the understanding about Earth and the planets.
It was a breakthrough discovery in science which helped in understanding the physics of how Earth and heaven (heavenly bodies) worked.
Therefore, this sentence contain the central idea of the whole text as it states how the discovery of gravity has connected the physics between Earth and other heavenly bodies.
