Coronas are formed by an interference pattern of light diffracted through tiny water droplets in the atmosphere. At times, up to three coronas, each with its series of blue-green-red rings, may concentrically appear around the center reddish-brown ring, called the aureole.
When photographing them, it’s best to block the sun so it doesn’t overpower the exposure. I have purposely enhanced the vibrancy in these images to more easily see the rings. They were captured today at 11:53 am as a high bank of altostratus overspread my house. (Search Amazon for my book Kaleidoscope Sky for more on such spectacular optical phenomena.)