Stars twinkle due to atmospheric refraction fo starlight . AS the stars are very far away, they behave as almost point sources of ligth. A son account of atmospheric refraction, the path or rays of light coming from the star goes on verying slighly, the apparehnt positon of the star fluctuates and the amount of starlight entering the eye flickers. So, sometimes, the star appears brighter and at some time, fainter. thus the starts twinkle.
