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Astronomy/Cloudless disk around the moon

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Moon
Moon  
Hi This is the first time I have ever seen such a thing.  See the attached picture.  Last night it was cold and cloudy, but there was a cloudless disk around the moon almost perfectly symmetrical in form.  It was as if someone had sucked out the clouds around the moon or punched a hole in the atmosphere.  What is this phenomena called?  It can't be a very frequent occurrence.  Sorry the picture is not the greatest, it is done with one of those auto focus automatic cameras.

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Hi Cliff

What you are seeing there is  a result of ice crystals in the air--they reflect the light of the moon at a certain angle of incidence, but inside of that angle they don't reflect the light--in fact, they can block it.

I am not sure what the dark spike at the bottom of the photo is--maybe something closer to the ground that also appears in the frame?

Hope that helps

Paul Wagner  

Astronomy

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Paul Wagner

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Astronomy and telescope making. Have made at least seven telescopes, both refractors and reflectors, and have spent 30 years looking at the nighttime sky.

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