Question

Why do we not see the shadow of aeroplanes and birds flying in the sky ?​

Answer 1

Answer:

When the bird is flying high in the sky the distance between the body and the surface of the Earth is too large and hence even though the light is obstructed by the bird's body it cannot cast its shadow due to the large distance

Answer 2

Because of geometric optics the shadow will be more diffuse when the object is higher in the sky.