Imaged by Doug Zubenel
6th September '07.
The feature is huge and visible as a bright pearly bluish aureole with a faint yellow to red edge.
Spurious darkening of the field edges by vignetting was carefully avoided when taking this wide angle image and it should always be kept in mind when a Bishop's ring is suspected.
Bishop's rings are a form of corona produced by scattering from very small (~1µm (1/1000 mm dia) particles, usually stratospheric dust or sulphate droplets from volcanic eruptions.
The source of the scattering particles in this sighting is not known. Tropospheric smoke from distant forest fires in Washington State is a possibility.
Image ©Doug Zubenel, shown with permission.