A Triangular Shadow of a Large Volcano

Why does the shadow of this volcano look like a triangle? The Mount Teide volcano
itself does not have the strictly pyramidal shape that its geometric shadow might suggest.
The triangle shadow phenomena is not unique to the Mt. Teide, though, and is commonly
seen from the tops of other large mountains and volcanoes. A key reason for the strange
dark shape is that the observer is looking down the long corridor of a sunset (or sunrise)
shadow that extends to the horizon. Even if the huge volcano was a perfect cube and the
resulting shadow was a long rectangular box, that box would appear to taper off at its top
as its shadow extended far into the distance, just as parallel train tracks do. The above
spectacular image shows Pico Viejo crater in the foreground, located on Tenerife in the
Canary Islands of Spain. The nearly full moon is seen nearby shortly after its total lunar
eclipse last month.