|Santa Maria Volcano Shadow
Marc Bernstein on the summit imaged the shadow cast by the Guatemala volcano. Some 1400m above the surrounding plain, Santa Maria remains active and in 1902 its eruption was one of the 20th Century's largest. ©Marc Bernstein
Mountain shadows are three- rather than two-dimensional. They are shafts of unlit air tens of miles long. From the shadow casting mountain's summit they all appear triangular regardless of the mountain profile. Santa Maria volcano is in fact roughly triangular but that does not matter, its shadow would be triangular anyway.
At right is a cubical mountain casting a shadow near to sunset. The shadow converges slightly because the sun is 0.5° in diameter but essentially it is a long prism of square cross-section. The second diagram shows the view of the shadow from the top of the cube. The prism extends away into the far distance and by perspective appears triangular.