Wednesday, March 21, 2018

Blue Ice

On my way back home from down state, I stopped south of the Mackinac Bridge to get pictures of the blue ice.  From what I hear, the ice at the Straits is only blue once every seven years or so. 

But why is snow the color white and ice can be blue?  Snow is white because all wavelengths of light is scattered and reflected at the boundary between snow and air. The white color of bubbles at the top of a dark beer work the same way—small pockets of air reflect and scatter visible light. Ice only appears blue when it is forms solid without air bubbles.  Thus, blue ice does not have bubbles to interfere with the passage of light. Without the scattering effect of air bubbles, light can penetrate ice undisturbed. In ice, the absorption of light at the red end of the spectrum is six times greater than at the blue end.  A lack of reflected red wavelengths produces the color blue in the human eye.

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