So, just follow these steps:

1. Stand on flat plane surface and look towards the horizon.

2. Use a binocular and see as far as you can.

3. Now, climb a tree having a supposing good height, just be careful in climbing, and then look again through the binoculars to the horizon.

You will notice that the higher up you climb, farther you are able to see.

Generally, we think that it is because of the obstacles on ground like trees, houses, etc. that are obstructing our vision, and climbing at a height we will see everything clearly—but this isn’t the true reason. Even if we stood on a completely clear surface with no obstacles between us and the horizon, we would see much farther from the greater height than we would on the ground.

This phenomenon is caused by the curvature of the Earth as well, and would not happen if the Earth was flat: