[Tig] Moon dogs

Richard Kirk richard at filmlight.ltd.uk
Tue Jul 14 21:09:45 BST 2009


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Dave Pickett sez...

> Last night looking at the moon over southern California there was a
> distinct cyan/blue halo with a point atop the moon.  I second and triple
> glanced and it looked like a triangular color halo.  I know a little about
> the Doppler effect of time shifting light but that sight was a first for
> me.  I don't think it was good ole LA pollution as it was distinctly a
> reflection being diffracted.  Who knew that you could gaze at the moon one
> night and see something new?
>
> Anybody have an idea about what caused that?  Maybe a "Northern Lights"
> type of solar energy bend?

You can get little ticks on either side of the moon due to diffraction by
hexagonal ice crystals very high in the atmosphere. There are called 'Moon
dogs'. There are rarer cases where ice forms in different shapes and can
give you bright spots in other places.

Cheers.
Richard Kirk
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