Bending of light rays when it pass from one medium to another towards or away from normal pathway is known as refraction of light.

This scientific phenomenon describes many illustrations of illusion in natural day to day life.
The most suited example is spoon in a water filled bowl that is never straight to naked eyes. The depth of a pond or streaming water seems not identified correctly. Other facts may include kingfisher catching fishes in sea.

What are all reasons for such refraction in nature that brings definite answerable questions to mankind.

The best research in this field of physics...