Light consists of tiny particles called photons

Light consists of tiny particles called photons and the amount of energy in each photon corresponds to its color.Red light has lower energy and longer wavelengths.Purple light has higher energy and shorter wavelengths.Sunlight offers all the photons of the rainbow,so a gas molecule can choose the photons that carry the exact amount of energy needed to shift the molecule to its next energy level.When this match is made,the photon disappers as the molecule gains its energy,and we get a small gap in our rainbow.