Circumscribed Halo

A circumscribed halo is a type of halo, an optical phenomenon that circumscribes a related phenomenon, the 22° halo centred on the sun.

When observed, a circumscribed halo is normally oval in shape and, at the points directly below and above the sun, lies tangential to the 22° halo. It form when, as the sun rises, the upper tangent and lower tangent arcs extend into each other and close in on the 22° halo. As the sun rises above 70° it essentially covers the 22° halo.

A circumscribed halo is more intense in colour than the 22° halo. Like many other halos, it is reddish on the inner edge, facing the sun, and bluish on the outer edge.