Sky Watch Friday III - April 18, 2008

Blue Sky
(It’s too cold to Swim)

On the Beach, Gulf of Mexico, Corpus Christi, Texas, USA

I’m a Scientist and I don’t know for sure why the sky looks so blue on a really cold damp morning before sunrise in the winter. Brrrr.

I suspect the reason is probably based on the fact that when light hits gas molecules, which are smaller than the wavelength range of light, it is scattered. This effect is called “Rayleigh Scattering”. Different wavelengths of light are scattered at different angles. Red, orange, and yellow light are more unaffected because they have longer wavelengths than the blue light, which is scattered more because of its shorter wavelength. Thus, the blue would have been predominately scattered back down through the clouds. Temperature, humidity and fog droplet size may also play some part in this effect.

The sky was overcast and there was a heavy fog bank back to the left where the sun was trying to rise and everything had taken on the color of that cold blue light from the sky. It was definitely too cold to swim! Even if the water had been bathtub warm, the psychological effect of that cold blue light would have shouted “It’s too cold to swim”. Just look at that sky.

I had to adjust the levels significantly on both ends, since the color was all spiked tightly in the blue channel. For those that don’t use Photoshop, let’s just say, everything was really dark and blue. And for you Photoshoppers, I used layers and a high pass filter to sharpen and cut through some of the fog to see out across the ocean.

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Troy and Martha