Fog Corona near Green Bay
October 14, 2006
The foggy sunrise of June 6, 2006 revealed a bit of beauty along a rural roadside near Green Bay, Wisconsin. Fog is basically the same as a cloud, but with its base close enough to the Earth's surface that it restricts visibility to less than 1 kilometer or about 0.6 miles (according to the definition by the U.S. Weather Bureau, Air Force, and Navy). Coronas, whether observed in fog or in mid altitude clouds, result from diffraction of sunlight rather than from refraction or reflection. Smaller droplets produce larger diffraction angles and thus a larger corona. The next time a shallow layer of fog accompanies the rising Sun, see if you can observe a corona (looking toward the Sun) or perhaps even a glory (looking away from the Sun) -- such morning magic just may brighten your day.