There's nothing triangular about the Mount Teide volcano. From its base, it's the third largest volcano in the world but is pretty flat on top. So why does its shadow look like a perfect ghost pyramid rising over the horizon?
Click image to enlarge to high definition.
The answer is simple: Perspective. This amazing photo was taken by Juan Carlos Casado from the top of the Teide. From his point of view, the perspective accentuates the shape of the volcano's shadow as it's projected by the Sun into the thick atmosphere, converting it into a triangle:
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.
It seems like a scene from a science fiction movie, perhaps the view from astronauts arriving to a new planet and discovering a titanic pyramidal structure in the distance, the remains of a long lost civilization. [TWAN via APOD]