Two Sides of the Same Ridge
One slope faces the sun and the other does not, and after a few thousand years they stop looking related.
Stand a ridge north to south in the northern hemisphere and its two flanks receive different amounts of light for the rest of their existence. The south-facing side dries out, warms early, loses its snow weeks ahead; the north-facing side keeps meltwater, holds a cooler soil, and grows trees that would die on the other bank. Botanists in the Alps have a name for the pair, and Chinese maps carry it in place names: the sunny slope and the shady slope of the same hill, often two villages apart.
Photographs of ridgelines end up recording this without meaning to. In one frame the left flank is bare grass and rock going pale in the afternoon, the right flank is dark conifer holding the shadow it has held since morning. The line where they meet is not drawn by anyone. It follows the crest, and it moves a little each century as the climate leans one way or the other.
On a screen the contrast does most of the work: a bright half and a dense half in one image, without a filter having been involved. It is a useful thing to notice when a mountain wallpaper feels balanced for no obvious reason. The balance was surveyed by sunlight, over a longer period than the photographer spent choosing the spot.
