Circumhorizon Arc Over La Rioja, Argentina

March 08, 2019

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March 2019 Viewer's ChoicePhotographer: Leandro Fernández Pohle
Summary Authors: Leandro Fernández Pohle; Jim Foster

The exceptionally colorful circumhorizon arc featured above sometimes referred to as a fire rainbow, appeared over the skies of La Rioja, Argentina, near noon on January 2, 2019. This arc forms when sunlight is refracted through the hexagonal ice crystals that compose cirrus clouds. However, the crystals must be similarly oriented so that when light enters a crystal's vertical side face it's then refracted through the lower horizontal basal face. For this to occur, though, the Sun must be more than 58 degrees above the horizon. Therefore these arcs can only be observed in the mid-latitudes near midday and during the late spring and summer. Use utmost caution when looking toward the Sun. See also the Earth Picture of the Day for February 6, 2019.

Photo Details: Taken with an iPhone 7 Plus camera; automatic mode.