antisolar arc 2018
© Pål Tengesdal
On May 21st, Pål Tengesdal boarded a plane at the Gardermoen Oslo Airport in Norway and took off. Minutes later he saw something strange out the window. "There was a bright luminous «X» in the clouds," he says. "I photographed it using my iPhone 7."

"The phenomenon was visible for less than 2 minutes," says Tengesdal. "As we moved out of the clouds it faded away."

Tengesdal witnessed a rare type of ice halo called "anti-solar region arcs." To see them, you have to stare directly away from the sun, looking down into icy clouds where subhorizon reflections from the faces of ice crystals create these strange arcs.

anti-solar arc 2018
© Pål Tengesdal
Tengesdal's seat in the plane was, for 2 brief minutes, the perfect viewing location. "I was seated on the side of the plane diametrically opposite the sun," he explains. "This put the plane's shadow in the diamond-shaped center of the «X» (e.g., the anti-solar point). Clouds floated in a thin layer below the plane."

Anti-solar region arcs are bright but elusive, requiring a passenger to be seated in just the right spot, looking in just the right direction, at precisely the right moment as the plane ascends above icy clouds. Rare, indeed.