August 8, 2010 in Idaho Voices

Haze makes for some beautiful sunsets


The skies have been rather hazy lately, thanks to recent wildfires across north central Washington. Fortunately, due to the lack of a big dome of high pressure across the Northwest, we have not had to compound the smoky skies with stagnant air, which would serve to trap all the smoke, in addition to other pollutants, and significantly deteriorate our air quality. While the smoke is not pretty to look at during the day, it has made for some pretty spectacular sunsets.

When the sun is high in the sky, and especially when the air is clean, the sun/sunlight appears white. That is because all the wavelengths of light are distributed equally in all directions, and to our eyes. When the sun gets lower on the horizon, the sunlight has to travel through a thicker portion of our earth’s atmosphere. Air molecules themselves scatter the shorter wavelengths of light, the blues and the violets, allowing the longer wavelengths to pass through. The gives us the yellow, orange and even reddish glow of sunsets. The size and concentration of particles in the atmosphere determine the distinct hues of the sunset. When the air is filled with particulate matter, such as smoke or dust, which is larger in size than air molecules, even longer wavelengths of light are scattered, including the yellows. This gives the sunset an even more orange and reddish glow. Deep red sunsets are produced when the sun’s light travels through an area with a high density of large particles, such as volcanic ash, or the salt laden air over the ocean.

Speaking of large particles, one in particular fell out of the sky in South Dakota recently and landed in the record books. During the evening of July 23, severe thunderstorms moved through central South Dakota, producing destructive straight line winds up to 80 mph, large hail, and a possible tornado. One of the hail stones ultimately discovered in Vivian, S.D., measured 8 inches in diameter 18.625 inches in circumference, and weighed 1.93 pounds! This broke the previous U.S. record for hail diameter set by a 17-inch hailstone found in Aurora, Neb. in June 2003. It also broke the record for hail stone weight, set by a 1.67-pound hailstone in Coffeyville, Kan., in 1970. The Aurora hailstone will retain the record for circumference which is 18.75 inches. It is interesting to note that the hailstone itself did suffer some damage when it hit the ground, and likely experienced some melting and sublimation (when a solid directly changes phase to a gas) before it was officially measured. We’ll never know how truly big it was.

Michelle Boss can be reached at

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