Sun halo over Lake Antermoia in the Dolomite Mountains of Italy

Rainbow around the Sun. Winter solstice

The days only get longer from here! The Northern Hemisphere marks the beginning of winter today, but the winter solstice is also the shortest day of the year. The rainbow that encircles the Sun here, a sun halo, is above Lake Antermoia, a glacial lake in the Fassa Valley, in the Dolomite Mountains of northern Italy. Sun halos form when sunlight or moonlight shines through ice crystals suspended in the upper atmosphere. When the light hits the crystals they serve as a prism, separating the light into individual colours of the spectrum, the same way rainbows occur after a rain shower.