If you’ve been paying attention to chemtrails, you may have observed rainbow smearing (diffraction) of light reflected off them. Dark sunglasses can bring the subtle rainbows into the dynamic range of the human eye. Chembows are often visible when the sunlight reflects at approximately 45• angle to the chemtrail. Wikipedia entry on diffraction
Diffraction is a quantum interaction between photons of light and edges of atoms. When metallic surfaces have features smaller than a wavelength of visible light (nanometer scale), different wavelengths will be reflected at different angles. When features are ordered in a linear pattern (such as on a DVD optical disc), a rainbow will appear.
In the rain, or other atmospheric conditions where water droplets are large enough, rainbows appear due to refraction. Atmospheric refraction (such as from a rainbow in a rainstorm) is a similar phenomenon to chemtrail diffraction. Its important to note, however, that rainbows can be seen in light reflected off chemtrails, not only refracted from behind, which may occur under other atmospheric conditions, such as the presence of large ice crystals or droplets.
More examples of chembows: