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?

Explanation

**Step-by-Step Solution:**

1. **Understanding Shadows**: Shadows are formed when an object blocks light from a light source, such as the sun. For a shadow to be cast on the ground, the object must be at a height where it can block the sunlight.

2. **Height of the Object**: On a sunny day, both birds and airplanes can fly at high altitudes. When they are flying very high in the sky, they may not cast a shadow on the ground because the angle of the sunlight may not allow their shadow to reach the ground.

3. **Conditions for Shadow Visibility**:
- **Low Altitude**: If a bird or an airplane is flying low, close to the ground, it can cast a shadow on the surface. This is because the light from the sun can be effectively blocked by the object, allowing the shadow to fall on the ground.
...