P-1 Refraction of light — Science STD 10 — Question

i. Stars are point sources of light as they are very far away from us.
ii. The density of air increases with lowering height just above the surface of the earth, its refractive index also increases. The starlight travels from a rarer to a denser medium and continuously bends towards the normal. This makes the star appear to be higher in the sky as compared to its actual position.
iii. The apparent position of the star keeps changing a bit. This is because of the motion of atmospheric air, changing air density and temperature. Because of this, the refractive index of air keeps changing continuously.
iv. Because of this change, the position and brightness of the star keep changing
continuously.