Why do stars twinkle?

Q. 10 :- Why do stars twinkle? 



The earth atmosphere consists of layers of different gases of varying density. Since the physical conditions of the earth’s atmosphere are not stationary. The refractive index of atmosphere goes on changing continuously. As the starlight, enters the earth’s atmosphere, it undergoes refraction multiple times before it reaches the eyes on earth. This makes the apparent position of the star changing slightly and continuously. Since the stars are very distant, they approximate point-sized sources of light. As the path of rays of light coming from the star goes on varying slightly, the apparent position of the star fluctuates and the amount of starlight entering the eye flickers – the star sometimes appears brighter, and at some other time, fainter, Hence the twinkling of stars.