A sun-cast shadow always falls in the exact opposite direction from the sun and grows longer as the sun's elevation angle drops closer to the horizon.
A sun-cast shadow always points directly away from the sun and grows longer as the sun drops toward the horizon, so shadow direction and length are fully predictable from the sun's position for any time and date. That predictability is what lets a photographer plan a shadow-driven composition instead of stumbling onto one.
A long shadow raking across a beach, hard geometric shapes down a city street, a subject's silhouette stretched along a wall: each needs a particular low sun elevation and a particular azimuth, both of which a sun calculator returns for a chosen moment. Get the timing wrong by an hour near midday and the shadows are half the length and pointing somewhere else. The length runs roughly with the inverse tangent of the sun's elevation, so it changes slowly around midday and very fast in the last hour before sunset.
A photographer planning a shot of a lone tree throwing a long shadow across a wheat field wants that shadow to run left to right through the frame and to be about three times the tree's height. Shadow length equals object height divided by the tangent of the sun's elevation, so three times height means an elevation near 18 degrees.
For that location in September, the sun passes 18 degrees at about 6:10 pm, on an azimuth of 258 degrees, which throws the shadow toward 78 degrees, close to due east. The photographer sets up on the west side of the tree, arrives by 5:45, and has a usable window of maybe fifteen minutes before the shadow stretches past the far edge of the field and loses its shape against the crop.