Before sunrise or after sunset, you might be gazing skyward and notice that there are beams of light that appear to be shooting out from horizon, or down from the clouds. These are crepuscular rays, sometimes called sunrays. They are beautiful, mysterious and very noticeable.
Crepuscular rays are columns of sunlit air, streaming through gaps in clouds or other objects (for example, mountain peaks). Darker cloud-shadowed regions lie between the sunlit columns. These rays are really parallel to each other. But they appear to diverge, much as a road that looks narrow in the distance appears wide beneath your feet.
Crepuscular means like twilight or dim. That’s a clue that this effect is normally seen before sunrise or just after sunset, when the sky is somewhat dark.
When you see the rays, the sun’s disk might be just below the horizon from your perspective, with the sun is shining through clouds in that part of the sky.
You need just the right conditions to see these rays. In other words, in order to see crepuscular rays, the clouds, the sun and you must all be in the right spot with respect to each other. Airborne dust, droplets of water and the air molecules themselves are what make the sunrays visible.
If you are seeing these rays in the east before dawn, remember to turn around and face west. You might be in luck and see fainter and less noticeable anticrepuscular rays. These rays form opposite the sun.
Bottom line: With just the right sky conditions, you might see crepuscular rays or sunrays around sunset, or after sunset. You can also see them shining through clouds.