The above image shows a good example of crepuscular rays. The name comes from their typical appearance during crepuscular hours (those around dawn and dusk), when the contrasts between light and dark are the most obvious. Crepuscular comes from the Latin word “crepuscular” meaning twilight.
A key component for crepuscular rays is the casting of a shadow. The shadow can be due to most anything, typically clouds, or as above, trees. The result is sunlight broken into darkened areas (in the shadow) and lighted areas.
However, these rays are not always visible. Their light needs particles to reflect off of, or scatter, to our eyes. In the above image, ice crystals help the light to scatter.
The visible beams always appear to spread out from the light source. In the above image the rays appear to converge at the sun and diverge as the light falls on frozen riverbed.
Here is where our story gets interesting. Although the light rays are actually parallel to each other, we do not perceive it as so. The rays appear to be heading straight down to the ground but are actually streaming from the sun to your eyes. Just like viewing a set of parallel railroad tracks, they appear to converge in the distance.
Here are just a few other names that been have used to denote these beams: Backstays of the sun, Cloud breaks, Divine Light, Gateways to Heaven, Stairways to Heaven, God Rays, Fingers of God, Jacob’s Ladder, Jesus Beams, Beams, Jesus Rays, Shafts of Light, Sun rays, Sunbeams and Sunburst.