On December 16th, the skies above Oslo, Norway, stunned onlookers with a display of ice halos that "looks set to go down in halo history as one of the greatest ever," says atmospheric optics expert Les Cowley.

Oslo resident Johannes Froyen describes the scene: "It was a beautiful day with tiny ice crystals falling from a clear sky. As I looked out my window, I was thrilled to see so many arcs and pillars of light." He took these pictures using a Nikon D70:

©Johannes Froyen
"Looks set to go down in halo history as one of the greatest ever."

The cause of the display was sunlight shining through diamond dust -- that is, tiny crystals of ice in the air near ground level. "Diamond dust makes the very best halos," says Cowley. "The Oslo display was widely seen and had several rare arcs.

The bright V shaped halo touching the 22 degree halo is an upper tangent arc. Outside that, the brightly colored arc is actually two superimposed halos, a supralateral arc made by horizontal pencil-like crystals and a very rare 46 degree halo made by tumbling crystals."

"The season of diamond dust is upon us in the Northern Hemisphere," he says. "Check the sky during the icy dawns and days of the next few weeks!"