Bishop's Ring

The Bishop's Ring was first described after the eruption of the Krakatoa volcano (August 27, 1883). During the massive explosion, the sound of which was heard even in Africa, 4800 km away, vast amounts of dust were hurled into the atmosphere, which for years provided incredibly vivid sunrises and sunsets. The first published observation of the ring comes from August 30, 1883, and appeared in the Japan Gazette. There, its appearance is described as a "faint halo" around the sun. The first detailed description came from Sereno Bishop, who observed the phenomenon on September 5, 1883, in Honolulu: "Allow me to draw special attention to the very peculiar corona or halo extending 20 to 30 degrees from the sun. It was visible here every day, and all day long. A whitish veil with pink coloring and purple or violet shadows against the blue background. I know of no other report of such a corona. It is a hardly noticeable object." The ring was subsequently named after Bishop.
Most observations agree that the inside of the ring is whitish or bluish-white and that the ring turns reddish, brownish, or purple towards the outside. The area enclosed by the ring is significantly brighter than the surroundings. Due to the color sequence (red outside), it can be concluded that it is a diffraction phenomenon, as e.g., with halos, red always lies on the inside. The radius of the ring is on average about 28°. This is a rather large radius for light diffraction, which can only be produced by very small dust particles (0.002mm), all of which must be nearly the same size. Very uniform, small aerosols responsible for the formation of the Bishop's Ring occur mainly during volcanic eruptions. After the eruption of Mount Pinatubo, a Bishop's Ring was observed in Japan for a long time. We will have to wait for the next major volcanic eruption to see bright and clear Bishop's Rings again.