Saturday, May 18, 2019


Last week, Marcella Giulia Pace of Livinallongo Col di Lana, Italy, looked at the bright sun, then turned away, squinting. To her surprise, she saw a luminous X in the sky. Blinking didn't make it go away. "It was a rare Wegener Arc," she says.

In the picture, above, the faint X-shaped Wegener Arc is bisected by a bright parhelic circle. They intersect just above the tip of the tree at a point in the sky directly opposite the sun.

Wegener Arcs are caused by sunbeams passing through pencil-shaped ice crystals in the clouds. For the arc to form, the sunbeam must enter through one face of the crystal, bounce off the inside, then exit through another face tilted 60 degrees with respect to the first. No wonder they're rare.

Above: The formation of the Wegener Arc. 

The bright parhelic circle is formed in a different way when sunlight shines through plate-shaped crystals. It is rare, too, but not as rare as the Wegener Arc. All in all, a lucky catch. "It made my day," says Pace.

Parhelic Circle & Wegener Arc
Taken by Marcella Giulia Pace on February 5, 2015 @ Livinallongo Col di Lana, Belluno, Italy

Rare Wegener Arc and Parhelic Circle in antheliac point

Camera: Nikon D7100; 18mm; 1/250; f22; ISO 100; two shot for panoramic.
Location: Livinallongo Col di Lana (Belluno), Italy

In this link the video:

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