Give scientific reasons : Stars twinkle.

Answer: Because of atmospheric refraction of starlight through air layers whose refractive index keeps changing.

• Stars are very far away and behave like point sources of light. Their light passes through many layers of air before reaching our eyes.
• The temperature and density of these layers keep changing, so their refractive index also keeps changing. The light is therefore refracted by different amounts from moment to moment.
• As a result the apparent position of the star and the amount of light reaching our eyes keep changing, and the star appears to twinkle.