EarthSky.org, 7/4/13
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.
