Regenbogen

Regenbogen is the German term for the meteorological optical phenomenon known in English as a rainbow. It is a multicolored arc that appears in the sky opposite a strong light source, typically the Sun, during or after rainfall.

Formation involves refraction, dispersion, and reflection of sunlight within individual raindrops. As light enters a drop, it is refracted and dispersed into its component colors, internally reflected off the back of the drop, and refracted again on leaving. The geometry concentrates light at specific angles relative to the observer, producing the visible arc. The primary rainbow forms at about 42 degrees from the direction opposite the Sun, with red on the outer edge and violet on the inner edge. A second rainbow can appear at roughly 50 to 53 degrees, with the color order reversed.

Observational conditions require water droplets in the atmosphere and a bright light source behind the observer. A low Sun enhances the brightness and width of the rainbow, while droplet size and distribution influence color intensity and the visibility of faint features such as supernumerary bows.

Variants and related phenomena include fogbows, which occur with very small droplets and appear pale or white; moonbows, which are rainbows illuminated by moonlight; and reflection rainbows, seen on the surface of still water. The rainbow is explained by optical geometry and, in finer detail, by wave optics, as the color separation depends on wavelength. The phenomenon has been observed across cultures and remains a common example in studies of atmospheric optics.