A rainbow is a visually stunning optical phenomenon, but it is not a physical object that can be touched. This inability to interact with the arc lies in the fundamental physics of light and human perception. The display is entirely dependent on the specific geometry between the sun, water droplets, and the observer’s eye.
The Science Behind How Rainbows Form
A rainbow is an optical phenomenon resulting from the interaction of sunlight with airborne water droplets. Sunlight appears white but is composed of the full spectrum of visible colors, each corresponding to a different wavelength. Rainbow formation begins with a combination of refraction and reflection inside these tiny, nearly spherical water droplets.
When a ray of sunlight enters a droplet, it bends, or refracts, because light travels slower in water than in air. This refraction separates the white light into its constituent colors, similar to how a prism works. The light then reflects off the inner surface at the back of the droplet. As the light exits the droplet, it refracts a second time, further dispersing the colors before they reach the observer’s eye.
The primary rainbow is formed by light that undergoes one internal reflection. Due to differing wavelengths, each color emerges at a slightly different angle, with red light emerging at a greater angle than violet light. This precise optical path creates the continuous spectrum of color we perceive.
Why Rainbows Are Not Physical Objects
A rainbow cannot be touched because it is not a tangible object occupying a fixed space. It is light, electromagnetic radiation, being scattered and directed toward the observer, making it a perceived image. While the water droplets are physical, the colored arc is merely the light processed through them and traveling through the air.
A rainbow is a visual effect, not a solid, liquid, or gas. The light forming the image comes from countless individual droplets suspended in the atmosphere. If you move toward a specific droplet contributing to the rainbow, that droplet will no longer be at the correct angle to reflect the light to your eye, and the color will disappear for you.
The display depends on light rays being bent and reflected at the specific “rainbow angle,” approximately 42 degrees for the primary bow. Since the rainbow is a concentration of light intensity at this particular angle, it is impossible to physically stand “in” or “under” the arc. The image is constructed solely by light correctly oriented to reach your pupils.
The Personal Nature of the Rainbow
The geometry that creates the rainbow is entirely dependent on the observer’s position, making it a highly personal phenomenon. To see a rainbow, the sun must be behind you, shining toward the airborne water droplets in front of you. The center of the rainbow’s arc is known as the anti-solar point.
This anti-solar point is the location directly opposite the sun from your perspective, often located within the shadow of your head. The rainbow always forms at a fixed 42-degree angle extending outward from this personal anti-solar point. Because the rainbow’s position is defined relative to you, it moves as you move.
If you walk toward a rainbow, the arc appears to shift away because you are constantly changing the necessary 42-degree geometric relationship. You are moving the axis of the entire optical cone, not approaching a fixed object. Every person standing at a different spot sees a slightly different rainbow, composed of light from a different set of water droplets.