Rainbows are formed when sunlight interacts with water droplets in the air through a process called refraction, reflection, and dispersion. When sunlight enters a water droplet, it slows down and bends (refracts) because water is denser than air. Inside the droplet, the light is reflected off the back of the droplet and then refracted again as it exits. This bending and reflecting of light cause the white sunlight to split into its component colors, creating a spectrum. The different colors bend at slightly different angles, with red bending the least and violet the most, producing the familiar multicolored arc seen in the sky. For a rainbow to be visible to an observer:
- The observer must have the sun behind them,
- The water droplets (from rain or mist) must be in front,
- The sun must be low in the sky (less than 42 degrees above the horizon).
The rainbow seen is actually a circular arc formed by light rays at a specific angle, typically about 42 degrees from the direction opposite the sun. Each observer sees a unique rainbow because the exact angle and position of the refracted light differ with the observer's viewpoint.
