Moons are always smaller than planets because a smaller body always orbits around a larger body because the larger body has more gravity.
Why are all of the planets round ? The gravitational force of a planet’s mass pulls all of its material toward the center and makes it round.
Our Planet Earth is called the Blue Planet because it appears blue when seen from sky. But why our “Blue Planet” is appears blue from sky?
Gravitational Force is the weakest force in Nature. However, it is very long ranged force. This gravitational force is always attractive in nature.
Strong nuclear force is the strongest force in nature. However, it is very short-ranged force and dominate only at the level of subatomic particles.
There are Four Fundamental Forces of Nature. These are Gravitational force, Weak Nuclear force, Electromagnetic force and Strong Nuclear force.