* Turbulence: Our atmosphere is constantly in motion, with pockets of air at different temperatures and densities. This creates turbulence.

* Light Bending: As starlight travels through these turbulent layers, it gets bent and refracted (changed direction).

* Varying Brightness: Because of the bending, the light from a star doesn't reach our eyes in a constant stream. Instead, the light is scattered, causing the star to appear to flicker or twinkle.

Think of it like this: Imagine looking at a star through a glass of water. The water is constantly moving, causing the light from the star to bend and change direction, making it appear to flicker.

Important Note: Planets don't twinkle as much as stars. This is because they appear as larger discs of light, so the light from different parts of the planet averages out, reducing the twinkling effect.