The planets do not twinkle because they are much closer to Earth than stars and appear as extended sources of light rather than point sources. The light from stars, which are extremely distant, behaves like coming from a single point. When this starlight passes through Earth's turbulent atmosphere, it refracts and causes rapid changes in brightness and position, leading to twinkling. In contrast, planets appear larger in the sky; their light comes from many points across their disks. Each point's light refracts differently through the atmosphere, but these variations average out, canceling the twinkling effect. Thus, planets look steady and do not twinkle.
Additional points:
- The atmosphere causes light refraction in layers of varying density, bending light rays (atmospheric refraction).
- Stars' tiny point-like light sources cause their light to shift brightness and position as refracted paths change.
- Planets reflect light from the sun and appear as small disks, so the multiple points of light refraction smooth out the apparent brightness changes.
- Some explanations also note that the light from planets is reflected and more monochromatic, which reduces twinkling due to less dispersion in wavelengths.
Hence, the key reasons for planets not twinkling are their relative closeness, larger apparent size, and the averaging effect of atmospheric refraction on their extended light sources.
