A fogbow (also called a white rainbow or ghost bow) is an optical phenomenon analogous to a rainbow but formed by the interaction of sunlight with the extremely small droplets of fog (typical diameter 10–50 µm, compared to 1–2 mm for rain drops). Its appearance is a white or faintly coloured arc opposite the sun, with a brighter interior than exterior. The chromatic difference from a rainbow is explained by diffraction: when drops are very small, diffraction broadens each spectral colour until it overlaps with adjacent ones, mixing the colours and producing a predominantly white band. Only at the edges are colour traces perceptible: a bluish tint on the outside and reddish on the inside. The arc's angle (~39°) is similar to a rainbow's (42°), but more diffuse. The fogbow is observed when the sun is behind the observer and fog lies ahead, typically during mornings when radiation fog begins to dissipate. It is common in mountains, coastlines, and over meadows with morning fog. From an aircraft, it can be seen as a complete circle surrounding the plane's shadow, often accompanying the glory. Although less striking than a rainbow, the fogbow has an ethereal, ghostly beauty appreciated by atmospheric phenomena photographers.