![]() ![]() This means that, at the edge of the disk produced by the red light, where it is the brightest, there is no light of other colours to compete with it, so the light looks red there.Ī bit closer in, at the edge of the orange disk, there is no light of yellow, green, or blue colors, since those disks are smaller ─ and, also, the light from the red disk is fainter, because it's not at the maximal-brightness edge and the orange disk does have its maximum shine there. The thing with this process, though, is that the maximal angle of aperture of the cone of light that's reflected by each droplet depends very sensitively on the refractive index of the water that makes up the droplet, and this refractive index also depends on the wavelength of the light, so that the size of the disk increases with the wavelength, with the red disk being the largest, then the orange, yellow, green, blue, indigo and violet being successively smaller. So what's with the colors?Īlthough your diagram's geometry is off, as you correctly note, the standard diagram (the first figure in this answer) is kind of misleading, because for it kind of implies that for every red ray that hits your eyes, there will be another droplet at another angle sending a yellow ray (or green, blue, orange, indigo, and so on) on the same path ─ and that is indeed correct! This is what happens inside this disk of light. This clustering means that, for each color, the disk of light has a particularly bright edge, called a caustic. This means that if the relative angle between the Sun, the droplet, and your head is smaller than a certain maximal angle $\theta_\mathrm$ (notice in the ray diagram that there's many more dots in that region than there are near the axis). But here's the important thing: the angle at which the light exits increases, has a maximum, and then decreases again, a fact which is clearly visible by following the dots as they go down from the negative- $x$ axis, stop, and then go back up again. (partially) reflect back when they hit the back of the droplet, and thenįor each droplet, though, there are a bunch of rays hitting the droplet at different locations, and each of them will bounce around differently and exit at a different angle, so that the end result looks like this:īecause there is a reflection inside the droplet, the light is mostly sent backwards, and because there are two steps where refraction happens, the angles are a bit wonky.When sunlight hits a water droplet, the rays will However, the real picture is a little bit more complicated. ![]() The standard explanation is that light bounces around inside each droplet, and getting reflected once, and exiting at an angle: ![]()
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