Crepuscular Rays (H. Michael Mogil, CCM, CBM, NWA-DS*)
We’ve all seen images with the sun’s rays shining through a forest, streaking through clouds in religious artwork, and gracing a child’s drawing of the Sun. These are known as crepuscular rays. They are most often seen at twilight (as the sun is rising or setting), but can be seen at anytime when clouds or other objects block some of the sun’s rays and there is a sufficient amount of particulate matter in the air to make the sun’s rays visible (Fig. 1). As a result, we see the sun’s rays with shadowed (darker) areas in between.
Crepuscular rays are most common on the side of the sky in which the sun is located. The rays emanate from the sun and fan out across the sky (Fig. 2). The sun (or origin of the rays) is the focal point for the rays. This ray pattern is exactly what children draw when they show a sun and its rays in their youthful artwork.
However, when the sun’s rays and shadows pass to the other side of the sky, perspective takes over and the rays appear to converge onto a point on the other horizon. Even though the rays are continuing to fan apart from their solar source, the rays appear to act differently on the far side of the sky.
These rays, because they are opposite to crepuscular rays, are known as anti-crepuscular rays.
If you are ever seated on the side of an airplane away from the sun, especially toward twilight, look for these anti-crepuscular rays (if present) to converge onto a point on the ground or the horizon. It’s worth a photograph or two.
© 2018 H. Michael Mogil
Originally posted 2/28/18
* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.