why do stars twinkle

Stars twinkle because their light passes through Earth's atmosphere, which consists of layers of air with varying temperatures and densities. These variations cause the light to bend or refract multiple times before it reaches our eyes, leading to a shifting and flickering appearance known as "atmospheric scintillation." This makes the stars appear to change brightness and even color slightly, producing the twinkling effect. The effect is more pronounced when stars are near the horizon because their light travels through more atmosphere compared to stars overhead. Planets and the Moon don't twinkle as much because they appear larger in the sky, and the multiple light rays from them average out the atmospheric effects, making their light steadier. In essence, stars themselves do not twinkle; the twinkling is an atmospheric optical illusion caused by the turbulent, changing conditions of the air through which the starlight passes on its way to Earth.