What Exactly Is a Rainbow?
A rainbow is a natural optical phenomenon that displays a spectrum of light in the sky. It appears when sunlight interacts with water droplets suspended in the atmosphere. For a rainbow to be visible, the sun must be behind the observer, and water droplets, such as rain or mist, must be in front.
The process begins when white sunlight enters a water droplet. As light passes from air into denser water, it bends or “refracts.” Different colors of light bend at slightly different angles, with violet light bending more than red light.
After refraction, light travels to the back of the water droplet and reflects off its inner surface. The light then refracts again as it exits the droplet and travels towards the observer’s eye. This sequence of refraction, reflection, and a second refraction separates white sunlight into its individual colors, creating the vibrant arc we perceive.
The angle at which colors are observed is consistent for each color. Red light, for instance, is seen at 42 degrees relative to the sun’s rays, while violet light appears at about 40 degrees. This angular relationship means each person sees a rainbow formed by light from different water droplets, making it a unique optical event.
The Unreachable End: Why It’s an Illusion
Reaching the end of a rainbow is not possible due to its optical nature. A rainbow is not a physical object located at a fixed point in space; instead, its appearance depends on the observer’s position relative to the sun and water droplets.
Because each observer sees a rainbow generated by light from specific water droplets at precise angles, the rainbow effectively moves as the observer moves. If you walk towards where you perceive the end of a rainbow, the required angle for light to reach your eyes from those droplets changes. New droplets then align at the correct angles to form a new segment, making the rainbow appear to constantly recede.
A rainbow is actually a full circle of light, not just an arc. From the ground, only a semi-circular arc is visible because the horizon blocks the lower portion. When viewed from a higher vantage point, such as an airplane, it is possible to see a complete circular rainbow.
The perceived “end” of a rainbow is simply where the arc appears to meet the ground from a particular viewing angle. Since this appearance is unique to each observer’s perspective and shifts with movement, there is no fixed, physical end to approach or reach. The notion of finding a tangible end to a rainbow is an illusion rooted in its optical nature.