Why do stars twinkle?
At one moment light in sky appears very bright while at other moment,it appears to be dull. This is called twinkling of stars
The twinkling of stars occur because the optical Density of air continuously changes from one layer of the atmosphere to another.
The continuous change of optical density in air refracts the light from the stars by different amounts at different moments.
Hence, when atmosphere refracts more starlight towards us,stars appear to be bright.
When they refract less light,stars appear to be dim.
Hence, the star light reaching our eyes change continuously and stars appear to twinkle.