The photo above shows the shadow of Tajumulco Volcano (13,845 ft or 4,220 m) in Guatemala , projected on the summit of Tacana Volcano. It was taken from Tajumulco's summit. If sufficient dust or aerosols are in the air, a mountain's shadow can be seen cast in the atmosphere . Sunlight outside of the shadowed area is scattered by the dust, but inside the shadow the scattering is greatly reduced, so the triangular shadow appears dark. Regardless of the shape of a mountaintop, because of perspective it's shadow is always triangular as viewed from the antisolar point . Note also the rosy fringe hugging the western horizon . This is the Belt of Venus ; the sunlit upper strip of the Earth's shadow on the atmosphere, as it sets in the west. Photo taken on January 18, 2015.