Refraction ‒ Rainbow

A rainbow is an optical phenomenon that appears as a series of concentric, colorful arcs, created by the refraction and internal reflection of sunlight in water droplets present in the atmosphere during rain or fog. As sunlight passes through individual droplets, it is refracted (bent) upon entering the droplet because water has a higher refractive index than air. The refractive index varies for different wavelengths of light, causing the light to be dispersed into its color components. Inside the droplet, the light reflects off the inner surface and exits at different angles, with each color bending slightly differently. Raindrops at the same angular distance from the sun appear to be the same color, which gives the rainbow its characteristic circular or semi-circular shape. In some cases, light can undergo multiple internal reflections within the droplet. When two internal reflections occur, a secondary rainbow can be seen above the primary one. This secondary rainbow has a reversed color sequence and is usually much fainter than the primary rainbow.