An observer can see a rainbow only when his back is towards the sun. The sunlight from his back falls on water droplets suspended in the air in front of her. It is refracted inside it and different colours of white light get separated due to refraction. These different rays strike the inner surface of the droplet and reflected if the angle of incidence is greater than the critical angle(nearly equal to 48∘). This reflected ray is again refracted into the air. Hence, rainbow formation is a combination of dispersion, refraction and reflection of light.