It is really an optical illusion created by the refraction and reflection of light. When sunlight passes through raindrops, the light bends, or refracts, as it enters the droplet, and then reflects off the inside of the raindrop. This happens because the water is more dense than the air that surrounds it. As it exits the droplet, the light separates into wavelengths. Visible light is made up of various wavelengths, and each wavelength appears as a different colour: red, orange, yellow, green, blue, indigo and violet. Red light, for example, bends at a different angle to violet light. This is why the person on the ground sees each colour at a different location, and why rainbows look like a bow or an arc.
