On May 21, Paul Tengesdal boarded a plane at Gardermoen Airport in Oslo, Norway. A few minutes later he saw something unusual in the window. As he said, a bright luminous letter "X", which he captured with his iPhone 7 camera, seemed to hover among the clouds. According to him, it could be observed for less than two minutes, and as soon as the plane left the cloud zone, it disappeared.
Tengesdal witnessed a rare type of halo - arcs around the anti-solar point. To observe the phenomenon, one must look directly from the sun, looking down at the icy clouds, where sub-horizontal reflections from the edges of the ice crystals create these strange arcs.
Tengesdal's seat on the plane was ideal for such an observation within two short minutes. He was just sitting on the side diametrically opposite to the Sun. The plane's shadow was at the diamond-shaped center "X" (at the anti-solar point - the point directly opposite the Sun), and the clouds hovered in a thin layer under the plane.
Antisolar arcs are bright but subtle - observing them requires the passenger to sit in the right place, looking in the right direction, at the very moment the plane rises above the icy clouds. All this makes the observation of such a phenomenon a rarity.