Have you ever wondered (or noticed) that shadows never have sharp edges? The reason for this is diffraction.
An object between the sun and the earth causes a shadow, because the light can not go through it. But these obstacles do not really stop the light. At the edges of the object light diffracts. Light is able to "go around the corner" and weaker, circular waves reach the earth in the place where is the shade.
How much a ray of light "bends" depends on the wavelength. The larger the wavelength, the sharper the corner can be. the larger wavelength change directions more readly than shorter wave lengths. The image on the right illustrates this effect.
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