Dubbele halo om de zon
Foto is gemaakt in Fairbanks, Alaska
Earlier this week, a winter storm passed through Fairbanks, Alaska. In its wake, "it left a lot of ice crystals in the air," says resident Bernard Marschner. "We had a beautiful display of sun halos--including this double halo on Jan. 17th."
The inner ring is a common 22 degree sun halo, caused by sunlight shining through ice crystals shaped like hexagonal prisms. The outer ring is something more exotic.
"It is a 46 degree halo," explains atmospheric optics expert Les Cowley. "They are more rare than many text books and websites would have you believe."
Both 22 and 46 degree halos are caused by the same hexagonal prism ice crystals, but the 46 degree halo is almost always too faint to see. When you see an outer ring, it is usually something else: "A supralateral arc," says Cowley. "These are caused by hexagonal column crystals aligned horizontally in the air and can masquerade as a 46 degree halo."
Marschnet's sighting was the real thing. "We might get more tomorrow with the temperatures supposed to fall to -50 F," he says.
Bron: http://spaceweather.com/
