Loandra Torres (Member 47,730) came face to face with a 22-degree halo and sun dogs near Pikes Peak, in the southern Front Range of the Rocky Mountains in Colorado, US. The 22-degree halo is the ring around the Sun. The sun dogs, also known as parhelia, are the bright spots on the halo level with the Sun to its left and right. This was likely a very cold day because these optical effects were produced by diamond dust, which needs very low temperatures to form.

Diamond dust is a subtle mist of ice crystals sparkling in the sunlight as they tumble through the air. It forms when the temperature is low enough and the air dry enough for water vapour to form directly as ice crystals, rather than first forming into droplets and then freezing. In the clean air of the Colorado Rockies, temperatures for diamond dust might have needed to be around −25°C (−15°F). When they form slowly in very cold and dry air, the crystals of diamond dust tend to grow into simple shapes, as hexagonal columns and hexagonal plates. These are just what are needed to act as tiny prisms that refract the sunlight and form effects like halos and sun dogs.