"Halos like this are caused by ice crystals suspended in the air. The crystals are hexagonal, and light entering one face of the hexagon gets slightly bent, and then bent again as it comes out. The total angle of bending is (at least) 22°, and this is what forms the ring 22° in radius.
Different colors are bent by different amounts; red is bent slightly less than blue, so the inner edge of the halo is red (look at the picture carefully and you’ll see that’s true). The inside of the halo is slightly darker than the sky around it, because no light is bent less than 22°. Light coming to you from the Moon inside that 22° limit gets bent away from you, so you don’t see it. Light outside that limit gets bent toward you, making the bright ring. The halo is actually pretty broad, but fades rapidly outside 23 or so degrees from the Moon, so it looks like a halo. In reality it’s more like a disk with a hole in it.
I love how Jupiter is sitting just outside the ring; in a couple of days the Moon will swing past the giant planet in our sky, missing it by just about 4° (roughly 8 times the size of the Moon’s disk itself). That’ll be a lovely sight.
(...)I’ve seen halos many, many times — though this one was really spectacular. Still, the reason I’ve seen so many is quite simple: I look up. Seriously, that’s all it takes. What glories of nature are you missing by not looking around you?"
fonte: http://blogs.discovermagazine.com/badastronomy/2011/11/07/ring-around-the-moon/
Aí...imagina ver isso da sua janela do avião???? não sei o que eu faria....
fonte: http://imgur.com/jPu9a
obrigada pelo presente @emcimadoteto! :)
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