The twinkling of stars is due to :     

The twinkling of stars is caused by the refraction of light. When starlight passes through the Earth's atmosphere, it travels through layers of air with varying densities and temperatures. These layers have different refractive indices, which bend (or refract) the light in different directions.

How it Happens

1. Atmospheric Layers: The Earth's atmosphere is not uniform; it consists of layers with varying temperatures, pressures, and densities.
2. Light Bending: As starlight passes through these layers, the light continuously bends due to changes in the refractive index. This bending causes the position and brightness of the star to appear to fluctuate.
3. Perceived Twinkling: The rapid changes in the bending of light create the illusion of the star's light flickering or "twinkling."

Why Stars Twinkle and Planets Do Not

• Stars are located at a very large distance from the Earth, so they appear as point sources of light. This makes the effect of atmospheric refraction more pronounced, leading to twinkling.
• Planets, on the other hand, are closer to Earth and appear as discs of light. The light coming from different parts of the disc averages out the effect of atmospheric refraction, so they do not twinkle as noticeably.

Summary

The twinkling of stars is due to the refraction of light caused by the Earth's turbulent atmosphere. This natural phenomenon adds a sparkle to the night sky, making stars appear to shimmer.