This Halo is not for Saints!

Our friend Marghita got this superb photo of a halo around the full moon. This is of the family "Sun Dog" -- and these come in several forms, including classic 'dogs' that are twin bright phantom suns 'dogging' the sun. 

Not limited to daytime, you'll often see them around the full moon, where they usually take on this full circle halo effect.

It is a sign of high thin cirrus clouds drifting 20,000 feet or more above our heads. These clouds contain millions of tiny ice crystals. The halos you see are caused by both refraction, or splitting of light, and also by reflection, or glints of light from these ice crystals. The crystals have to be oriented and positioned just so with respect to your eye, in order for the halo to appear. 

Because of this, they are highly personal -- the halo YOU see will never be exactly the same as that seen by the person standing beside you with a slightly different viewpoint. But we can all enjoy Marghita's photo!

There is an old folk saying "halo around the moon brings rain soon."  That's because (remember the bit about the high clouds full of icy crystals?) they indicate that there is a lot of moisture up there... and what is up, almost always at some point comes back down.