Question

why do stars appears twinkling?​

Answer 1

Stars appear twinkling due to atmospheric refraction

Short answer but to the point

Mark as brainlist please

Answer 2

Stars twinkle due to atmospheric refraction of Starlight.  As the stars are very far away, they behave as almost point sources of light. On account of atmospheric refraction, the path of rays of light coming from the stars goes on varying slightly, the apparent position of the stars fluctuate and the amount of Starlight entering the eyes flickers.  Sometimes, the stars appear brighter and at some other time, fainter.  Thus the stars twinkle