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 in our image, a sun halo, is above Lake Antermoia, in the Dolomite Mountains of northern Italy. Sun halos form when sun or moon light shines through ice crystals suspended in the upper atmosphere. When the light of the sun hits the crystals they serve as a prism, separating the light into individual colors of the spectrum, the same way rainbows occur after a rain shower.