After rain, some of the water droplets remain in the air. When sunlight falls on these rain droplets, these drops behave like small prisms. The sunlight refracts two times from the rain drops, first from the back side of the prism then from the front of the prism. When light ray refracts from rain drops or small prisms, it is divided into different wavelengths. In other words, light ray splits into its components or different colors. The seven colors of rainbow are violet, indigo, blue, green, yellow, orange and red.
The regular rainbow we see in the sky, which arouses awe and excitement, is formed by light playing on water drops as they fall. Each raindrop acts as a tiny prism, breaking down the sun's white rays of mixed light into their component spectral colours. Occasionally droplets of mist can cause a rainbow, but generally it is the larger raindrops. No two persons see the same rainbow. Each individual sees the rainbow from his particular point of view, because a rainbow is only light coming from a certain direction. Since the drops reflecting the light are falling, this means that we see a new rainbow formed by every new set of raindrops. Sometimes a second rainbow may appear in the sky, lying outside the first and shining rather more faintly. The colours in this rainbow are in the reverse order, with blue on the outside and red on the inside. This is because the light rays have undergone one more reflection on the internal surfaces of the raindrops and are reversed in much the same way as left becomes right and right becomes left in a mirror. But this extra reflection causes a reduction in intensity of the light, which is why the second rainbow is always dimmer.
As a ray hits the outer edge of the round raindrop, it is bent (refracted) and dispersed or separated into different colours (different lengths of light waves). Then these separated light waves hit the far side of the raindrop and are turned back (reflected). On their leaving the raindrop, more bending of the waves takes place. How does this cause all the colours of the rainbow; present theory holds that each colour that you see is formed by rays that reach your eye at a certain angle, and the angle for that colour never changes. The top band, for example, is red because that portion of the raindrops is at about a 42-degree angle from your eye. It is at that angle that your eye will pick up the red light waves. The other six colour bands below the red (orange, yellow, green, blue, indigo and violet) occur at angles slightly less than 42 degrees.
