Question

what is the reason of twinkling of stars

Answer 1

The reason for twinkling of stars is the phenomenon called "Atmospheric Refraction"

Earth's atmosphere is not uniform. It contains layers of air of different​ densities. In general, on moving upwards, density decreases. So, light coming from stars is refracted.

Next, the composition is not uniform at any given instant. There are fluctuations in the components of air in a given volume. So, it's density also fluctuates. As a result, the light coming from stars is refracted more or less from its path. So stars seem twinkling

Answer 2

star are the point size source of light

hence the ray of light caming from stars varying slightly which cause apparent postion of star fluctuated and the amount of light caming from star its flickers and sometimes the starlight light appear brighter some time fainter which is the reason behind the twinkling of star

and for your knowledge planets not twinkle because the planets are much closer to the earth and and the stars lights are point size but planets light light are collection of points sized sources which is the reson that the planets are not twinkle .

the above both question are very important if you are perparing for board class 10 exam ..... so i suggest you dont forget to learn it before exam

best of luck if you are class 10 student . i am also a student of class 10