November 7, 2008 in Keepers Log, More Logbook

Fog bow

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Water temperature: 42 degrees. Relatively warm, moist air in contact with the cold river creates fog in the valley. Thick fog on the river this a.m. The morning sun shone through the fog and created a fog bow. A fog bow is like a rainbow but without the color, a ghostly white cloud-like arc in the sky. Sailors dubbed them “sea-dogs.” Fog bows lack color because the relatively small size of water droplets in fog. Light is not simply refracted or reflected by the fog droplets as in rainbows. Instead, the light is diffracted due to the wave properties of light. Diffraction or scattering of sunlight by the small droplets prevents clearly defined ray paths, washing out any color bands and causing a “white rainbow.”




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