Why do stars twinkle at night?

Stars twinkle at night because their light passes through Earth’s atmosphere, which causes it to refract or scatter. As the light travels through layers of air with varying temperatures and densities, it bends in different directions. This creates the appearance of a flickering or shimmering star. The effect is more pronounced when stars are near the horizon, as their light passes through more atmosphere. This phenomenon, known as stellar scintillation, does not occur for planets as their light comes from a broader source, making them appear steady in the night sky.