Why do stars twinkle but planets do not?

Stars twinkle, while planets do not, due to the differences in their sizes, distances from Earth, and the way their light interacts with the Earth's atmosphere.
1. Size and Light Source:
• Stars appear as point sources of light because they are so far away from the Earth. The light from a star has to pass through the Earth's atmosphere and undergoes many small changes due to atmospheric turbulence. As a result, the light from a star is refracted in different directions, causing it to appear to fluctuate in brightness, a phenomenon we perceive as "twinkling."
• Planets, on the other hand, appear as tiny disks rather than point sources of light. While planets are also distant, their apparent size is larger because they are much closer to Earth compared to stars. This means the light from a planet undergoes less noticeable refraction, and the fluctuations in brightness are not as significant, making the planet's light appear steady.
2. Atmospheric Interference:
• The Earth's atmosphere is made up of layers of air with different temperatures and densities. This causes the light from celestial objects to refract or bend in different directions as it passes through these layers. The greater the distance the light travels through the atmosphere, the more it gets refracted.
• Since stars are much farther away than planets, their light passes through more layers of the atmosphere and is more affected by the atmospheric turbulence, causing the star to appear to twinkle.
• In contrast, planets are much closer to Earth, so the light from a planet passes through less of the atmosphere and is less subject to such turbulence. This results in a steadier appearance.
3. Effect of Atmospheric Disturbances:
• The twinkling of stars is primarily caused by "stellar scintillation," which refers to the random fluctuations in the brightness of a star as its light is bent by the moving air in the atmosphere. These fluctuations are much more noticeable for stars due to their point-source nature.
• Planets do not exhibit such noticeable fluctuations because their larger apparent size averages out the effects of atmospheric turbulence, making them appear as steady light sources.
Conclusion:
• Stars twinkle because they appear as point sources of light and their light is significantly affected by the Earth's atmospheric turbulence.
• Planets do not twinkle because they appear as small disks, and the light from them is less influenced by atmospheric turbulence, making their brightness more stable.
Thus, the key reason why stars twinkle but planets do not is the difference in how their light interacts with the Earth's atmosphere due to the stars being much farther away and appearing as point sources of light, whereas planets are closer and appear as disks.