Question: Why do stars twinkle?

Stars twinkle because of the atmosphere of the Earth. The atmosphere is turbulent as hot air rises and cold air drops, as well as winds and mixing of the atmosphere close to the ground. The different pockets of air of different temperatures and sizes refract the light waves coming from the stars differently, it is like inserting a million little magnifying glasses between us and the star, and wiggling them around. The result is that sometimes the starlight is refracted away from us, sometimes towards us, sometimes making the star look brighter or dimmer. That is the twinkling effect. Twinkling is particularly noticeable after a hot day, when the ground heats the air near the surface of the Earth. All the hot air rising makes the atmosphere turbulent and the stars twinkle strongly. Part of the reason stars twinkle is because they appear almost as point sources, because they are so distant. Objects with a larger angular size do not twinkle as strongly, which is the origin of the saying “stars twinkle, planets don’t”. Planets appear quite large, because they are quite close to us.