Why do stars twinkle?

            Stars are giant glowing balls of fire situated far away from us. Many of them are several times larger than our sun, but being very far away, appear as points of light. Stars themselves don’t twinkle but appear as steady points of light when seen from space where there is no atmosphere. The twinkling of stars as seen from ground is caused by the unsteadiness of the Earth’s atmosphere. When light from an extended source such as the Sun, Moon or the planets pass through the atmosphere, it does not appear to twinkle because the slight changes in apparent brightness in one part is usually compensated by light coming from another part of the celestial object. But when light from a point source like a distant star passes through the atmosphere the fluctuations in the light intensity is not                                                                                       compensated and the star appears to twinkle.