What is the reason of twinkling of Stars ?

Q: What is the reason of twinkling of Stars ?

Sol: Density and refractive index of the air decrease with height above the earth’s surface. This causes the light from the stars and other heavenly bodies to bend as it passes through the atmosphere. When we look at stars, quite often they do not appear steady. They disappear for a fraction of second before reappearing or their positions seem to shift slightly in random directions. This event is called as twinkling of stars since the temperature of air and its humidity are not the same everywhere in the atmosphere. The refractive index of air varies between different masses (or pockets) of air, even at light from a star may pass through one or more such pockets in the atmosphere before reaching the eye. Due to this, the final direction of the ray reaching the eye also changes, causing the image of the star to shift in random directions or directions or disappear for a while. The amount of starlight which reaches the eye also keeps changing due to shift in the direction of the of the light. As a result, the perceived brightness of the star fluctuates .