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Twinkling Stars

Why do Stars Twinkle ?

 Out in space, stars do not twinkle. It is only when you look at them from Earth that they appear to do so. Stars are really very large but they are so far away from us that they seem to be just points of light. 
     Starlight comes towards Earth along a path through space that produces very little change in the light. However on Earth we see stars by looking through our planet's atmosphere, which is a thin shell of gases surrounding
our planet. The Earth's atmosphere is in constant motion, with pockets of hot and cold air moving around constantly. Light rays bend differently in cold air and hot air. The motion of hot and cold air pockets causes the light rays from a star to move continuously too. In addition, the pockets of moving air also focus and defocus the starlight, so that its brightness keeps changing. Both of these effects together produce the sensation that we call 'twinkling' of stars. 

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