why do stars twinkle

Stars appear to twinkle because of the way the Earth's atmosphere affects the light that passes through it. As light from a star enters the atmosphere, it must travel through layers of air that have different temperatures and densities, which cause the light to refract or bend. This bending of the light causes it to follow a slightly different path than it would if the atmosphere were uniform, and as a result, the star appears to be moving slightly in the sky and to change in brightness.

The movement of the light causes the star to appear as if it is flickering or twinkling. The amount of twinkling depends on the density and temperature of the atmosphere, as well as the angle at which the light is entering it. Stars that are closer to the horizon tend to twinkle more because their light must pass through more of the atmosphere, which causes more refraction.

In space, where there is no atmosphere to cause the bending of light, stars would not appear to twinkle at all.