Bishop Ring seen Sept 11, '08 by Claudia Hinz (Claudia's Atmospheric Optics Site) on 1700m high Mount Wendelstein in Germany. Wendelstein Church, the highest in Germany, hides the sun.Image ©Claudia Hinz, shown with permission.
Claudia reports that on the 11th very fine sand had blown into Germany from the Sahara forming a layer at 12km altitude. Above that at 17-18km were particles from volcano Kasotochi. The sand and volcanic particles are scattering and diffracting sunlight to form a giant corona. Coronae do not need transparent particles and the smaller the scatterers the larger is the corona.
These immense coronae from fine sand, forest fire smoke and stratospheric volcanic dust are known as "Bishop's rings" after the post Krakatoa observation by Rev. Bishop.