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 they see their shadow on the ground?

Hint: We need to understand the criteria for the formation of shadows by objects with respect to the light source and the screen. The shadow formation is dependent on the distance of the object of hindrance to light and the screen where it is to be formed.

Complete step-by-step answer:
We know that the shadow is the dark area with the outline of an object which blocks the path of light on ground or a screen near to the object. The shadow formation, like the image formation, has requirements to form.
                 
The shadow formation needs three main requirements. They are –
1.A light source: This is why shadow cannot be formed in dark.
2. An object: The path of light needs to be blocked by the object to cast shadow.
3. A screen: The dark shadow due to the blocking of light can be seen only on screen which is kept behind the object not far from it.
The size of the shadow decreases with the increase in the distance between the screen and the object. For this reason, the shadow of an object.

Note: The formation of shadow and the length of the shadow is also dependent on the angle at which the light is falling on the object. This describes the difference in length of the shadow of ourselves in the mornings and evenings to be longer than in the noon.