We observe twinkling of stars due to

The twinkling of stars, scientifically known as stellar scintillation, is primarily caused by atmospheric refraction [1]. As starlight enters the Earth's atmosphere, it passes through various layers of air with different densities and temperatures [1]. These atmospheric conditions are not stationary; constant movement due to wind and thermal currents causes the refractive index of the medium to fluctuate continuously [1]. This causes the light to bend at slightly different angles as it travels toward the observer, leading to rapid changes in the star's apparent position and brightness [1]. While stars are indeed at a great distance, making them appear as point sources of light, the actual 'twinkling' effect is an atmospheric phenomenon rather than an intrinsic property of the star itself [3]. In space, where there is no atmosphere to refract the light, stars appear as steady, unblinking points.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > Twinkling of stars > p. 168
2. [3] https://en.wikipedia.org/wiki/Twinkling