Why Do Stars Twinkle?
What distorts the light coming from a star is temperature variations in the air. As you probably know already, air temperature varies a great deal.
The temperature variations in the air bends the star light so that it seems to change in brightness and the stars appear to twinkle. People got the idea that stars have points because they twinkle. The scientific name for the twinkling of stars is stellar scintillation (or astronomical scintillation).
Stars closer to the horizon appear to twinkle more than stars that are overhead – this is because the light of stars near the horizon has to travel through more air than the light of stars overhead and so is subject to more refraction.
Actually, stars are huge balls, like the sun. If we could see them from outer space, where there is no atmosphere, we would see stars shining with a steady light.