>>16701981 (OP)This.
It's also why many mistake mountains for hills in photos from the surface of the moon. Without an atmosphere to scatter light, it's difficult to judge scale and distance.
There are also no recognizable objects of known size, such as a tree or shrub. Rocks and craters are fractal in nature, a big one looks similar to small one if you have no sense of scale.
In pic related you instantly understand the distance because of the atmospheric scattering causing the distant mountains to appear hazy and blue.