Why do stars appear to twinkle when viewed from Earth?
Stars appear to twinkle because their light passes through Earth’s atmosphere before reaching our eyes. The atmosphere is made up of layers of air with different temperatures and densities. As starlight travels through these constantly moving layers, it is repeatedly bent and redirected, a phenomenon known as atmospheric refraction.
Because the atmosphere is always moving and changing, the amount and direction of this bending also change rapidly. This makes a star’s apparent brightness and position fluctuate slightly, creating the familiar twinkling effect. The effect is more noticeable when stars are close to the horizon because their light travels through a greater amount of atmosphere.
Interestingly, planets usually appear to twinkle much less than stars. Stars are so distant that they appear as tiny points of light, making atmospheric disturbances more noticeable. Planets, being much closer to Earth, appear as small disks rather than point sources, so the effects of atmospheric turbulence tend to average out.
