Question

what causes atmospheric refraction??mention its 2 effects..

Answer 1

Atmospheric refraction is the shift in apparent direction of a celestial object caused by the refraction of light rays as they pass through Earth's atmosphere. The twinkling of stars and variation in size of the Sun are due to atmospheric refraction of starlight.

Answer 2

The atmosphere of Earth is not evenly distributed, it is optically and molecularly denser at the bottom and and becomes rarer as we up, so the velocity of light changes from layer to layer. The molecules of different gases and dust partcles have different optical densities , moreover the hot air is optically rarer than cold air. These factors form differnt layers of air with different optical densities and thus cause the atmospheric refration.