by Chris Peterson » Fri Apr 02, 2010 3:10 pm
biddie67 wrote:If the cloud cover were consistent all around the area of the moon, could a circle of reflected light be seen at that distance?
I'm not sure what you're asking. If the clouds were more uniform, it is possible that the lunar halo and moondogs would be more uniform as well. But it depends not just on the uniformity of the clouds, but on their composition.
I've seen circles around the moon before but they were a lot closer than the 22 degrees described above - can the ice-crystals vary enough in their positions to cause the different positions of the moondogs or circles?
No. The 22° radius halo is the smallest true ring that can form around the Sun or Moon, and is the only possible radius for sundogs. Water droplets (or ice under the right conditions) can cause a broad glow around the Sun or Moon, a corona. This is always much smaller than a halo. It usually shows a faintly colored fringe that might make you think of a ring, although it is still quite different from a true halo. Perhaps this is what you saw, or perhaps you just misestimated the apparent size of a 22° halo on the sky.
[quote="biddie67"]If the cloud cover were consistent all around the area of the moon, could a circle of reflected light be seen at that distance? [/quote]
I'm not sure what you're asking. If the clouds were more uniform, it is possible that the lunar halo and moondogs would be more uniform as well. But it depends not just on the uniformity of the clouds, but on their composition.
[quote]I've seen circles around the moon before but they were a lot closer than the 22 degrees described above - can the ice-crystals vary enough in their positions to cause the different positions of the moondogs or circles?[/quote]
No. The 22° radius halo is the smallest true ring that can form around the Sun or Moon, and is the only possible radius for sundogs. Water droplets (or ice under the right conditions) can cause a broad glow around the Sun or Moon, a corona. This is always much smaller than a halo. It usually shows a faintly colored fringe that might make you think of a ring, although it is still quite different from a true halo. Perhaps this is what you saw, or perhaps you just misestimated the apparent size of a 22° halo on the sky.