Solar Halo and Parhelic Circle Over La Rioja, Argentina

February 06, 2019

Double sun halo (1)

Photographer: Leandro Fernández Pohle
Summary Authors: Leandro Fernández Pohle; Jim Foster

February 2019 Viewer's ChoiceFeatured above are a magnificent 22 degree solar halo and a parhelic circle as observed from La Rioja, Argentina, on January 2, 2019. Both were particularly conspicuous around midday. The parhelic circle is a narrow band of light that encircles the sky at the same elevation as the Sun -- it seemingly passes through the center of the Sun. Rarely are they seen as a nearly complete circle and seldom do they appear as vivid as this one. They form in cirrus clouds when sunlight reflects from the front surface (face) of any hexagonal ice crystal lying in the vertical plane. However, these crystals must be similarly oriented. Note that because ice crystals primarily reflect light rather than refract it, the halo or arc is devoid of color.

22 degree halos (so named because they're found 22 degrees from the Sun) take shape whenever sunlight refracts through pencil-shaped ice crystals (60-degree prisms) that are more or less randomly oriented. Always use extreme care when looking in the direction of the Sun.

Photo Details: Taken with an iPhone 7 Plus camera; in automatic and panoramic modes.