Tuesday, March 13, 2012

Unusuall Winter Rainbow over Lake Superior

Well sort of. Temperatures yesterday were in the 40s and 50s so it didn't feel like winter. I drove over to Agate Beach to see what was happening with the snow melt. There is no snow left on the beach, but the shore ice is still hugging tight. The mounds, however, have shrunk with the warm temperatures. While standing at the end of the boardwalk in a light mist, all of a sudden the sun came out and the most unusual rainbow appeared low to the horizon out over Lake Superior.

So what is a rainbow anyway? We probably all think we know, but do we really think about it? A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines on droplets of moisture in the Earth's atmosphere. It takes the form of a multicoloured arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun at an angle of 42 degrees. The rainbow is not located at a specific distance, but comes from any water droplets viewed from a certain angle relative to the Sun's rays. Thus, a rainbow is not a physical object and cannot be physically approached. Even if an observer sees another person who seems "under" or "at the end" of a rainbow, the second observer will see a different rainbow further off-yet, at the same angle as seen by the first observer.

In a "primary rainbow", the arc shows red on the outer part, and violet on the inner side. This rainbow is caused by light being refracted while entering a droplet of water, then reflected inside on the back of the droplet and refracted again when leaving it. The order of colors in a rainbow are: Red Orange Yellow Green Blue Indigo Violet.

In a double rainbow, a second arc is seen outside the primary arc, and has the order of its colors reversed, red facing toward the other one, in both rainbows. This second rainbow is caused by light reflecting twice inside water droplets. The region between a double rainbow is dark, and is known as "Alexander's band" or "Alexander's dark band".

Rainbows can be caused by many forms of airborne water. These include not only rain, but also mist, spray, and airborne dew.

While on the boardwalk, I also took a picture of the lighthouse showing the shore ice.  Notice how the shore ice looks darker in color than the pictures posted over the last few weeks.  As the ice starts to melt, the sand contained in the shore ice is consolidated.

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