Why does the moon sometimes appear larger in the sky? The size of the moon is an optical perception that is influenced by clouds and the horizon.

The figure illustrates the hypothesis of the apparent distance of the moon. A cloud of a certain size at a certain height in the atmosphere results in a smaller angle to the horizon than if it were higher up. Since the moon makes almost the same angle regardless of how close it is to the horizon line, it is perceived as larger when it is lower.