A pale disk of light surrounding the Sun, with a faint reddish-brown outer zone having inner and outer boundaries of about 10° and 20° when the Sun is highest. The radii increase at lower Sun elevations. Other colours (notably a bluish tint) have been reported but may arise through observers’ different colour perceptions. First reported after the eruption of Krakatau in 1883, and observed after certain subsequent volcanic eruptions, the phenomenon is thought to be caused by diffraction of sunlight by fine dust or sulphur dioxide particles in the upper atmosphere.
Subjects: Meteorology and Climatology.