Why stars twinkle?

Why stars twinkle?

PROF WAQAR HUSSAIN

            Stars twinkle for two main reasons. The intensity of brightness of stars decreases and increases because of the line-of-sight effect. Moreover, there are disturbance in the gases of the atmosphere around the Earth. Different layers of gases also have different temperature which brings visual changes. The atmosphere is moving around, and there are various currents of different density and temperature, etc. 

           when you look up at star, you are viewing them through 100 miles of atmosphere. The light of stars pass through different density of air, hence it is refracted again and again and when the current of air flow and light of stars have to pass through different sets of air densities, their refraction pattern is changed and consequently the viewer see the light of different intensity and at different places, this appear to viewer as twinkling.