Why do stars twinkle at night?

Stars twinkle because air wiggles above us. Their tiny lights jiggle in the sky. Our eyes see sparkle, sparkle. Planets look steadier and less jumpy.

Stars shine with steady light, but that light must pass through moving air around Earth. The air bends the light a little this way and that, so the star seems to flicker. It is like looking at a coin through wiggly bath water: the coin is still, but it looks jumpy.

Stars twinkle because their light passes through Earth’s atmosphere, the blanket of air around our planet. That air is always moving in warm and cool patches. Each patch bends the light a tiny bit, called refraction, so the star’s tiny point of light seems to dance and change brightness. Fun fact: stars do not twinkle for astronauts in space, because there is no wiggly air in the way.