During sunset near the refugio on Pico del Teide in an altitude of 3200 meters you can see the shadow of the vulcano rising above the horizon.
Here the observer is already inside the
mountain shadow and you can see an effect of a 'shadow
path' pointing radially away from the mountains top which is located left above the observer (click the image for a close up view).
This effect is because of light scattering of nearby
atmosphere particles.
The line of sight of the observer, looking in the direction above the
shadow of the mountain's top, is divided in an unilluminated and an illuminated part.
Where the dark part is longest,
the atmosphere appears darkest. This leads to a visible shadow
path reaching from the real mountain top to the shadow
of the mountain top.
The white domes on the right hand side belong to the
Teide observatory.