The Durham Herald Sun has this cool story:
DURHAM — Triangle residents have a few more weeks to view a rare and beautiful atmospheric phenomenon that has references in Homer’s Odyssey.
It is the phenomenon of “crepuscular rays”, beams of sunlight in the twilight in the few weeks between late November and early January. In Durham, the beams are formed when the sun sets behind the western mountains, with the mountain peaks casting shadows across North Carolina and the valleys between them letting rays of sunlight pass through.
The phenomenon is rare because it requires a coincidence of cloud-free air over the whole distance and into Tennessee, enough dust particles in the air to be illuminated by the sun beams, and a proper alignment of the path of the sun with prominent mountain peaks and valleys. The nearly pristine skies of early winter set the conditions that make viewing possible.
The beauty comes from the contrast of the deep blue sky at twilight with the rose-colored rays. It is this color that Homer referred to in the repeated phrase “rosy-fingered dawn” in the Odyssey.
Exactly which mountains and valleys are responsible for the rays in Durham is still not clear. When the sun sets in Durham, it is still moving northward below the horizon as it sets farther in the west. My best guess is that the rays travel through the long mountain valley from Clyde through Asheville to Black Mountain.
To have a chance of seeing the crepuscular rays, a good location with a largely unobstructed view of the horizon is required. Large parking lots at stores and malls with a good view of the western sky are suggested.
Sometimes the rays are clearer in one direction than the other and are most easily seen near the horizon. The rays start appearing almost exactly 20 minutes after local sunset time and can last for up to eight minutes before disappearing. At this time of year, sunset is no earlier than 5 p.m., and the rays may be seen during a commute home after work.