Colorful Clouds Over Cerro Pachón

A rainbow cloud creates a stunning curtain of colors just after sunrise in this image taken from Cerro Pachón in Chile, home of one half of the International Gemini Observatory, the SOAR Telescope, and Vera C. Rubin Observatory, all operated by NSF’s NOIRLab. The appearance of pastel pigmentation sweeping across the sky is possibly due to the phenomenon known as cloud iridescence. Similar to the swirling colors on the surface of a bubble or oil spill, this optical effect occurs when sunlight passes through a particularly thin cloud that is composed of water droplets or ice crystals of uniform size. As the Sun’s rays encounter individual crystals, the light is both diffracted and scattered, revealing a gradient of the component wavelengths, or colors, that make up the Sun’s light.

Because of the smooth, wavy shape of the clouds in this image, they closely resemble a different class of iridescent clouds called nacreous clouds, which are also produced by uniformly sized ice crystals diffracting sunlight. But unlike regular iridescent clouds that form in the troposphere and can be seen all over the world, nacreous clouds form at a higher elevation, in the stratosphere, and most often in frigid regions such as Antarctica, Alaska, and Scandinavia where the lower stratosphere cools below – 85° Celsius (–120° Fahrenheit).