Iridescent Clouds over Chile | Earth Science
Iridescent clouds, as seen from Gemini South Telescope in Chile, one half of the International Gemini Observatory, operated by the National Science Foundation (NSF) NOIRLab.
Cloud iridescence or irisation is a colorful optical phenomenon that occurs in a cloud and appears in the general proximity of the Sun or Moon. The colors resemble those seen in soap bubbles and oil on a water surface. This fairly common phenomenon is most often observed in altocumulus, cirrocumulus, lenticular, and cirrus clouds. They can appear as bands parallel to the edge of the clouds. Studying the colors in iridescent clouds tells scientists something about particle size within the clouds and how they may grow over time.
Ice-crystal clouds can exhibit brilliant spots or borders of colors, usually red and green, observed up to about 30° from the sun.
This irisation results from an optical diffraction phenomenon, usually of several orders. The cloud particles that cause this phenomena are very small (a few micrometers), and locally all are of nearly the same size; they result from local near adiabatic lifting and condensation. In general, the physical process where a vapor becomes a liquid or solid; the opposite of evaporation, although on the molecular scale, both processes are always occurring. in moist air often in a lenticular (wave) cloud, in pileus above a developing cumulus, or occasionally in irregular patches of uniform color in a region of shallow convection. (Note: In this case, they are often called a mother-of-pearl cloud).
Chile, officially the Republic of Chile, is a country in the Southern Cone of southwestern South America. It is the southernmost country in the world and the closest to Antarctica, extending along a narrow strip of land between the Andes Mountains and the Pacific Ocean.
Gemini South Telescope in Chile:
https://noirlab.edu/public/programs/gemini-observatory/gemini-south/
Date: Oct. 22, 2026
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