What is the reason behind the twinkling of stars?Is it due to pollution or refraction of light?

refraction of light from disturbances in the atmosphere(wind currents and such) it isn' noticeable over short distances or with very bright lights(say, the sun) or with close objects like the planets.

The stars themselves don't twinkle, but the turbulance in our atmosphere makes them appear that way, as was noted in the post above. In fact, anything that has a non-zero apparent size from our sky will not twinkle; the stars do because from Earth they appear as point-like objects.

 

Here's more info:

 

 

http://curious.astro.cornell.edu/question.php?number=114

or with close objects like the planets.

It's not exactly because they are close. Planets are close enough that they are actually a visible "Disc". When atmospheric disturbances distort this, instead of being completely refracted away form our eyes, because it is a disc, only some of the light gets refracted away, and another part of the disc gets refracted to our eyes. This is why they don't winkle.

 

Stars, although much, much bigger than a planet are far enough away that they appear as a point of light with no discernible disc. When the atmosphere diffracts the light, all the light from that star is diffracted away from our eyes and it is no longer visible for a fraction of a second (and then it is refracted back as the disturbance moves on).

yeah, i should have made that distinction. thanks ed.