We have seen that rainbows looks so colorful as we are only able to see only the visible light. But Do they also have ultraviolet bands and infra-red bands, that we are unable to see? I know someone has already asked the same question but I am concern about the specific ultraviolet and infrared bands only rather than any other wavelength.
Answer
Refraction of light in water droplets, leading to the formation of rainbows, is not limited to the visible range.
Experimental evidence, compelling due to its simplicity, is shown in the following images taken by University of College London Earth Sciences professor Dominic Fortes. Check the alignment of the rainbow with respect to the trees in each of the pictures. The UV band lies to the left of the visible band, while IR is found to be shifted to the right.
The spectral limits in a rainbow can be explained more technical by looking at the refractive index dispersion of water vapor, which can e.g. be found at refractiveindex.info. The UV, visible and near IR range lie in the wavelength region between 0.2 and 2.85 µm. The change in refractive index with respect to the wavelength leads to differing refraction angles and therefore a separation of the colors, as we know it from experience. Basically, this concept could also be extended to further wavelength ranges. Although the resonance around 2.9 µm leads to higher refractive indices for longer wavelengths again. Therefore light with a wavelength of e.g. 4.3 µm would overlay with light at 0.4 µm (both with a refractive index of 1.34). Yet, this is again only half the truth. If you look at the transmittance curve (further down on the same page), you can see that wavelengths longer than 1.8 µm are absorbed by water vapor. Therefore this is the realistic long wavlength end for rainbows. I assume similar arguments could be found for the short wavelength end, but I can't find experimental data.
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