Question

Why do star appers to twinkle?​

Answer 1

due to multiples of reflections in the sky

Answer 2

Answer:

Due to atmospheric refraction

stars are very far from us, so they behave as point source of light. since the physical condition of the earth's atmosphere are not constant the light from star appears to come from different directions. This results in fluctuation of apparent position of star.

The amount of light coming from stars also vary due to changing the refractive index of atmosphere.

the star appear bright when more light from star reaches our eyes and the same star appears dull when less amount of light reaches our eyes.

Both two effects are responsible for twinkling of stars.