Bishop's Ring

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A Bishop's Ring is a diffuse brown or bluish halo observed around the sun in the presence of large amounts of dust in the stratosphere. It is typically observed after large volcanic eruptions. The first recorded observation of a Bishop's Ring was by Rev. S. Bishop of Honolulu, after the Krakatoa eruption of 1883.

Bishop's Ring was first described after the eruption of the Krakatoa volcano on August 27, 1883. This gigantic explosion, threw a vast quantity of dust into the atmosphere which caused unbelievable colorful sunrises and sunsets for several years. The first observation of this ring was published in 1883 being is described as a “faint halo” around the sun. The first exact description was made by Sereno Bishop who observed the phenomenon on September 5, 1883, in Honolulu; the phenomenon was subsequently named after Bishop.

Most observations agree that the inner rim of the ring is whitish or bluish white and that its outside is reddish, brownish or purple. The area enclosed by the ring is significantly brighter than its surroundings. From the sequence of colors with the red on the outside one can conclude that the phenomenon is caused by diffraction because halos always have their red part on their inside. In average, the radius of the ring is about 28°. This is a rather big radius which can only be caused by very small dust particles (0,002 mm) which all have to be of about the same size.

Very homogeneous and small aerosols, such as those responsible for the appearing of Bishop’s Ring, are mainly caused by volcanic eruptions. So Bishop‘s Ring was observed for a longer period of time in Japan after the eruption of Mt. Pinatubo.