Why does the area inside the rainbow look brighter than outside?
The light that causes the rainbow emerges out of water droplets at every possible angle up to the radius of the rainbow. So, the light that interacts with the droplets and which reaches your eyes, forms a disk of light, with the colored rainbow at its perimeter. Outside the rainbow, there is no light exiting raindrops in the way that produces the main rainbow. Hence this area appears darker than the area within the bow. The dark area outside the rainbow is called Alexander’s dark band. • What is a red rainbow? What causes it? White light consists of all wavelengths of light (the whole continuous range) that we can see with our eyes. The rainbow forms in water droplets that decompose this white light into the range of wavelengths (colors). If the sun is low in the sky, the sun is reddened due to atmospheric adsorption (by dust) and by Rayleigh scattering (responsible for the blue sky). That means that only the red part of the color spectrum causes the rainbow, and hence the bow appears
