The answer to whether you can drive through a rainbow is definitively no. The reason lies in the nature of the phenomenon itself, which is a purely optical effect rather than a tangible object. To understand why it remains out of reach, we must explore the physics of how light and water interact to create this spectacular display. The arc you see is a momentary illusion born from precise atmospheric conditions.
Light, Water, and Refraction
A rainbow is an optical phenomenon resulting from the interaction of sunlight with suspended water droplets, each acting as a tiny prism. When a ray of white sunlight encounters a spherical raindrop, it first refracts, or bends, as it passes from the air into the denser water. This initial bending separates the light into its constituent colors.
The light ray then travels to the back of the droplet, where it undergoes internal reflection. Finally, the light refracts a second time as it exits the water droplet and travels toward the observer’s eye. This double refraction and single reflection direct the light back toward the person viewing it.
The separation of colors occurs because each wavelength of light bends at a slightly different angle during refraction—a process known as dispersion. Red light, which has the longest wavelength, bends the least, while violet light, with the shortest wavelength, bends the most. This mechanism arranges the spectrum, positioning red on the outer edge of the primary rainbow arc and violet on the inner edge.
The Role of Perspective and Geometry
The fundamental reason you can never reach a rainbow is that its appearance depends entirely on your specific location relative to the sun and the rain. The rainbow is always centered on a point directly opposite the sun from the observer, known as the anti-solar point. You must have the sun at your back and the rain in front of you to see the effect.
The colored light reaches your eyes from water droplets that form a precise cone with an angle of approximately 42 degrees around the anti-solar point. Every person sees a different rainbow because the specific droplets reflecting light into one person’s eyes are different from the droplets reflecting light into another person’s eyes.
As you drive toward what appears to be the rainbow’s location, the geometry of your position changes instantly. The droplets that were reflecting light at the required 42-degree angle to your eye are no longer doing so. New, farther-away droplets move into the exact position needed to maintain the 42-degree angle, making the rainbow appear to move away at the same speed as your vehicle. Since the rainbow is a visual angle and not a physical destination, it is impossible to drive through it.
Experiencing the Full Rainbow
While a rainbow is an optical effect that cannot be traversed, the familiar arc shape we typically see is only a partial view of its true form. The light geometry that creates the phenomenon is actually a complete 360-degree circle. The reason we usually see only a semicircle is that the ground blocks the lower half, preventing us from seeing the light reflected by water droplets below the horizon.
To witness the complete circular shape of a rainbow, a high altitude is necessary to bring the lower portion of the arc into view. Full-circle rainbows are most often reported by pilots or passengers flying in aircraft, who are high enough to see water droplets and mist below their horizon. The phenomenon can also be observed from the top of a tall building or mountain, or by looking down into a mist or spray from a high vantage point.