Corona (optical phenomenon)

In meteorology, a corona (plural coronae) is an optical phenomenon produced by the diffraction of sunlight or moonlight (or, occasionally, bright starlight or planetlight)[1] by individual small water droplets and sometimes tiny ice crystals of a cloud or on a foggy glass surface.

In its full form, a corona consists of several concentric, pastel-colored rings around the celestial object and a central bright area called an aureole.

[2][3] The aureole is often (especially in case of the Moon) the only visible part of the corona and has the appearance of a bluish-white disk which fades to reddish-brown towards the edge.

Coronae differ from halos in that the latter are formed by refraction (rather than diffraction) from comparatively large rather than small ice crystals.

They are more easily seen during sunset or sunrise as there is less sun glare and the light path through pollen laden atmosphere is longer.