Definition

A whitish ring, centred on the Sun or Moon, with a slightly bluish tinge on the inside and reddish brown on the outside.

- World Meteorological Organization (WMO-No. 49, Annex I)

Description

Bishop's rings are a form of corona or illuminated ring produced by the diffraction of light passing through a cloud of very fine volcanic dust, or sulphate droplets from volcanic eruptions, in the high atmosphere. They are unlike other coronas or haloes which are produced by water droplets or ice crystals. The colours of a Bishop's ring are not very distinct. They are particularly faint in rings observed around the Moon, which usually show only a pale red fringe.