White Shadows

March 06, 2018

Frost_shadow-20171115-081431-zoom (2)

Photographer: András Horvath 
Summary Author: András Horvath 

Fall and winter can produce a number of unusual and also beautiful phenomena. This photo shows one of them: a white shadow of a chimney on a roof. Even the projection of the holes at the top of the stack is visible.

This white colored shadow can be surprising for a moment, but the explanation is obvious. The photo was taken just after sunrise on a cold early winter morning. As dawn approached, frost accumulated on exposed surfaces including the roof of this house. When the morning Sun hit the roof, the frost crystals sublimated in just a few minutes. Naturally, the shadowy areas preserved the frost until the air temperature surpassed 32 F (0 degrees C).

This image is the result of fortuitous coincidence. The direction of the rising Sun in December is nearly parallel to two of the vertical sides of the chimney. Therefore, its shadow is rectangular, and the sunlight can go through the holes at the top. Since the apparent daily motion of the Sun is significant, the position of the frost-shadow and the real shadow are not entirely the same. Moreover, the image of the holes shows a motion-blur-like effect because the angular velocity of the Sun is too high for this slow photosensitive surface. Note also the triangular patch of frost on the image at right. Photo taken on December 15, 2017.

Photo Details: Nikon D5200 camera; focal length 55mm;: 1/250 sec. exposure; Aperture f/8; ISO; 140.