The physical phenomenon responsible for rainbows is the refraction, dispersion, and reflection of light. When light passes through raindrops in the atmosphere after a rain shower, it bends (refraction) as it enters and exits the droplet. This bending causes the light to spread out into its component colors, creating the spectrum that we see as a rainbow. The colors appear in a specific order: red, orange, yellow, green, blue, indigo, and violet. This optical phenomenon requires both sunlight and moisture in the air, making it a beautiful visual effect.