Stars do not twinkle if they are viewed from space. Twinkling star can only be observed from earth surface. So, why do star twinkle if viewed from earthsurface?? Actually, it is due to refraction of light. We know the light from the star passes through atmosphere before reaching to an eye of an observer on the earth. The atmosphere is not still as there are always hot and cold air. The hot and cold air from the layer of air of different densities. Due to the current of air, the density of the layer of air keep on changing continuously. This causes the position of the image o star to change ,continuously with time in space. As the change in density is in small range, the image of star appears to move within small area in the space due to refraction of light of the stars and this give rise to twinkling effect.
