Parallax Effect Demonstration
Demonstration of how the perceived distance covered, and thus speed, of an observed object, relative to an observation point moving in the opposite direction, changes depending upon the altitude of the observed object.
Both the white boxes are moving at the exact same speed and distance, yet, from the observation point (green box) the distance they cover (and thus their speed) would appear to be very different.
This effect is greatly exaggerated if scale of the observed object is unknown, especially if there is a featureless surface lacking reference points (such as a desert or ocean) is below the observed object.