regnbue

A regnbue is a meteorological-optical phenomenon in which multicolored arcs appear in the sky. It arises when sunlight is refracted, dispersed, and reflected inside raindrops. For a viewer on the ground, a primary regnbue forms as sunlight enters a raindrop, is refracted and dispersed into its component colors, reflects off the inner surface, and exits the drop again, bending the light twice. This geometry yields an arc seen at an angle of about 42 degrees from the line opposite the sun, with red on the outer edge and violet on the inner edge. A secondary regnbue can appear when light is reflected twice inside the droplets, producing a fainter arc with reversed color order at roughly 50 to 53 degrees.

Other related variations include supernumerary rainbows, caused by interference effects among light waves in small droplets, and occasional tertiary or higher-order bows that may be visible in particular atmospheric conditions. The phenomenon requires a combination of sun, rain, and an observer with a clear horizon, and is most often seen when the sun is low in the sky, such as after a rain shower.

Etymology and distribution: The Danish word regnbue combines regn (rain) and bue (arc). Regnbuer occur globally under suitable weather, and while they carry cultural symbolism in many societies, the scientific explanation remains the same.