Why Do Stars Twinkle

Why Do Stars Twinkle?


The twinkling of a star is due to atmospheric refraction of starlight. Stars appear as an only point size in the sky, because they are very far away from us.  The star light on entering the earth atmosphere undergoes refraction continuously before reaching to the earth due to slowly changing refractive index of various layer of atmosphere. The apparent position of star is not fixed but keeps varying and slightly, since the physical conditions of earth atmosphere are continuously changing. So the star light flux entering the eye fluctuates with time. Due to this, the star appear brighter and at some other time fainter. Thus the fluctuating apparent position of the star gives rise to the twinkling effect of the star to the eye. 



Stars nearer to the horizon appear to twinkle more than stars that are above your head - this is because the star light near the horizon has to travel more distance in air than the light of stars above your head.  The scientific name of this twinkling effect is stellar scintillation.

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