Monday, August 12, 2013

Patch Springs Fire Optics

The Patch Springs Fire in the Skull Valley west of Salt Lake City put in a great optics display last night, creating a red hue in much of the sky and a blood red sun.

The reddish hue is the result of a phenomenon known as Raleigh scattering, the scattering of light by particles that are much smaller than the wavelength of the light.  As you might recall from high school physics, Roy G. Biv (Red, Orange, Yellow, Green, Blue, Indigo, and Violet) describes the visible spectrum arranged in the order of decreasing wavelength.  Colors with shorter wavelengths at the end of the Roy G. Biv spectrum are scattered more by smoke than those with longer wavelengths at the beginning of the spectrum.  Thus, more of the longer, redder wavelengths of light survive transit through the smoke, leading to the reddish hue and the blood red sun.

As the sun set, we observed the shadow of the smoke move up the Wasatch Mountains, especially near Mount Olympus.  This shadow had a distinct red tint.  In particular, in the lower image below, contrast the color of the rock on upper Mt. Olympus with that of Thunder Mountain and Lone Peak in the right of the photo which were not in the shadow. 

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