Anticrepuscular Rays and Alpenglow

August 10, 2020

Ragggi anticrepuscolari venas copia 2

August  2020 Viewer's ChoicePhotographer: Marcella Pace
Summary Author: Marcella Pace

Rays that converge behind a mountain make us believe that the Sun is behind it, but it’s not in this case. Here, though the mountain peak is illuminated by the Sun, it’s in front of it not behind it. How is this possible? Anticrepuscular rays! These rays appear on the opposite side of the Sun at sunset (or sunrise) and seem to converge on the horizon opposite the true position of the Sun, creating the illusion that the Sun is at the point where they converge.

Anticrepuscular rays, in reality, are parallel and cross the entire celestial vault from west to east. Perspective makes it appear that they converge. They’re an extension of crepuscular rays, even if the latter don’t always manifest themselves or are clearly visible at the same time. I’ve noticed that, unlike the crepuscular rays, it seems that the alternation of the shadow rays of the anticrepuscular rays is wider than the rays of light as if the fan of the anticrepuscular rays was the negative of the crepuscular rays.

This photo was taken just before sunset on May 14, at Valle di Cadore (Belluno), Italy. The mountain peak is part of the Dolomites -- a World Heritage Site. Note that the top of the mountain is still illuminated by the Sun, creating an Enrosadira or Alpenglow effect.

Photo Details: Nikon D7100 camera; 18mm; 1/15 second exposure; f/7,1; ISO 100. Taken at 5:21 p.m. on May 14, 2016.