Atmospheric refraction, caused by varying densities in the Earth’s atmosphere, bends light from stars and planets. Stars, being distant point sources, appear to twinkle due to this bending and the fluctuating brightness as light paths change, according to Doubtnut and Filo. Planets, being closer and appearing as extended sources, have their light paths’ variations averaged out, preventing the twinkling effect. How refraction takes place in the atmosphere:
Varying refractive indices:
The atmosphere is composed of layers with different temperatures and densities, leading to variations in the refractive index (how much light bends when passing through a medium). Bending of light:
As light travels from outer space into Earth’s atmosphere, it undergoes continuous refraction (bending) as it passes from a less dense to a denser medium.Why stars twinkle but not planets:
Stars as point sources:
Stars appear as point sources of light due to their immense distance. Light from a star undergoes multiple refractions as it passes through the atmosphere, causing its apparent position and brightness to fluctuate, resulting in the twinkling effect. Planets as extended sources:
Planets are much closer to Earth and appear as extended sources (disks) rather than point sources. Because they appear larger, variations in the atmospheric path of light are averaged out across the planet’s surface, making them appear to shine steadily. Averaging out effects:
The turbulence of the atmosphere causes variations in the light path from different points on a planet’s surface. However, these variations tend to average out, preventing the noticeable flickering that stars experience.