As we can see in the image, it is a rainbow as we are used to seeing in the sky, but instead of having its ends down, it has them up; that is, appearing as an inverted rainbow (as if the sky were smiling at us, literally).
This particular photograph was taken in Ragusa, Sicily, on February 24 by Italian astrophotographer and primary school teacher Marcella Giulia Pace , 47, when the sun was low in the sky.
How are they formed?
Classic rainbows make up a multi-colored arc made up of water droplets hitting the light, and since water is denser than air, the light passing from the air into a raindrop at an angle slows down and changes direction. Part of the light that enters the drop is reflected internally from the inner edge of the drop and undergoes the phenomenon of refraction as it passes from the water to the air, thus separating the spectrum and showing the different colors of the rainbow in the visible spectrum (violet, blue, light blue, green, yellow, orange and red). In essence, light bends through the crystals in the cloud and separates the colors.
According to NASA, the zenith of circumzenithal or inverted arcs is in the center and the red color is on the outside, unlike traditional rainbows, after a downpour whose arcs point towards the horizon. The difference lies in the shape of the particles through which the sunlight is refracted (in traditional rainbows it is a droplet and in inverted or circumzenithal ones, hexagonal ice sheets ).
They are common?
The US space agency points out that to see them, you have to look up when the sun is low in the sky. This type of rainbow is usually associated with cirrus clouds, where ice crystals form easily. They occur throughout the year although they are usually hidden in the clouds.
And not only is the position of the observer important for viewing this inverted rainbow, but also the height, depth and position of the ice clouds so that the light enters at the specific angle convex to our star.