The light is refracted at the surface of the raindrop. Rains Rainbow LGBT shirt When this light hits the back of the raindrop, some of it is reflected off the back. When the internally reflected light reaches the surface again, once more some are internally reflected and some is refracted as it exits the drop. The reason the total internal reflection is most intense at about 42° is that this is a turning point light hitting the outermost ring of the drop gets returned at less than 42°, as does the light hitting the drop nearer to its center. There is a circular band of light that all gets returned right around 42°. If the sun were a laser emitting parallel, monochromatic rays, then the luminance or brightness of the bow would tend toward infinity at this angle (ignoring interference effects) and A WHITE RAINBOW FORMS ALL OVER THE SKY. All raindrops refract and reflect the sunlight in the same way, but only the light from some raindrops reaches the observer’s eye.
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So in order to get a natural rainbow, you need to have the sun Rains Rainbow LGBT shirt which emits the light) and the water droplets – Rain – (which act as a prism). That means rainbows can only appear when it is raining and you have a visible sunny zone somewhere in your field of view at the same time. The bright bands in each photo are called caustics. Note in particular how, in the glass of water and rainbow photos, there is no light on one side of the bright bands, but a little on the other. (The same thing occurs in the swimming pool, but is harder to isolate). Most explanations of rainbows show only a single ray of sunlight hitting a raindrop, and imply that it separates into the colors to make a rainbow. This is quite wrong. Think of all the light that hits the raindrops at the same time. This shows some of it.