Question

why are stars twinkle​

Answer 1

Stars twinkle because of turbulence in the atmosphere of the Earth. As the atmosphere churns, the light from the star is refracted in different directions. This causes the star's image to change slightly in brightness and position, hence "twinkle."

Answer 2

Stars twinkle because their light must pass through pockets of Earth's atmosphere that vary in temperature and density, and it's all very turbulent. On rough nights, a star appears to shift position constantly as its light is refracted this way and that.