Of mountains with perfectly triangular shadows

Anyone who has read Arthur C. Clarke's The Fountains of Paradise and been impressed by the description of the holy mountain with the perfectly triangular shadow must look at today's NASA Astronomical Picture of the Day, which shows (and explains, and links to a more detailed explanation of) such a shadow being cast by Mount Teide:

(See also, tangentially to which, my post on the identification of Jebel Musa as Mt Sinai.)