A rainbow is a natural spectrum of sunlight in the form of bows appearing in the sky when the sun shines on rain drops.It is combined result of reflection, refraction and dispersion of sunlight from water droplets, in atmosphere.Always it formed in the direction opposite to the sun.To see a rainbow, the sun must behind us and the water droplets falls infront of us.When a sunlight enters into a spherical rain¬drop, it is refracted and dispersed. The different colours of light bent in different angles.When different colours of light fall on the back inner surface of drop, it (water drop) reflects (different colours of light) internally (total internal reflection).The water drops again refracts the different colours, when it comes out from the raindrop.After leaving this different colours from the raindrop as rainbow, reach our eye. Thus, we see a rainbow.

A rainbow is formed due to the interplay of three factors namely, Reflection which is the bouncing back of light waves after striking an object, Rarefaction which is the bending of light rays on the interface of two media and Dispersion which is the separation of colours depending on their wavelength.