G'day Steemians, check out this spectacular photo of a "halo" by Judith Ward from my local area in Victoria, Australia!
This optical phenomenon is known as a "halo" or "22° halo" because it is a ring of light roughly 22° in radius around the sun. It is caused by the reflection and refraction of sunlight by very small suspended ice crystals in the high-level Cirrostratus cloud. The ice crystals behave like prisms and mirrors, refracting and reflecting light between their faces. This process directs light outwards away from the sun with little light reflected towards the inside of the ring, leaving the sky inside the ring noticeably darker than the sky outside of the ring, giving it the impression of a "hole in the sky".
There's an old weather saying "ring around the moon or sun means rain soon" which is partially correct as the high-level Cirrus cloud that forms halos often occurs ahead of an approaching cold front that can produce a rain band ahead of the cold front and showers following the cold front. As in this case, the Cirrostratus was forming ahead of an approaching cold front.