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The Golden Gate Bridge in San Francisco, California, as refracted through rain drops on the window of an automobile, which act as lenses. In optics, refraction occurs when light waves travel from a medium with a given refractive index to a medium with another, whereupon the wave's phase velocity is altered, causing the wave to change direction; its wavelength increases or decreases but its frequency remains constant.
Photo credit: Mila Zinkova
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