i.
The
stars emit their own light and they shine at night. The stars are point sources
of light as they are very far away.
ii.
During
refraction of starlight from the atmosphere, as starlight bends towards the
normal, the apparent position of the star is slightly higher then its actual
position.
iii.
Also
this apparent position of the star is not stationary but changes slightly.
iv.
Because
of mobility of air and changes in the temperature, the atmosphere is not
steady. Hence refractive index of air in the given region goes on changing
continuously and randomly.
v. When the atmosphere
refracts more light towards us, the star is seen bright. When the atmosphere
refracts less light towards us, the star is seen dim. Thus due to change in the
refractive index of atmosphere, stars appear twinkling at night.
