Why does an aeroplane flying at a great altitude not cast a shadow on the earth ?

On a sunny day, does a bird or an aeroplane flying high in the sky cast its shadow on the ground? Under what circumstances can we see their shadow on the ground?

Why do aeroplanes having wings fly at low altitudes?

What is a shadow and why the house fly does not cast a shadow on the ground while flying ?

Why does a cloudily track from behind an aero plane flying at a great altitude?

Assertion :- Bird flying high up in air does not cast shadow on the earth ground. Reason :- The size of bird is smaller than sun and sun is an extended source of light.