A spectral halo
with an angular radius
of about 46º occasionally seen in a cirrostratus
around the sun
. Like the 22º halo
, it is caused by refraction through randomly-oriented ice crystals
and is sometimes accompanied by sun dogs
- brighter, more colourful patches at or just outside its edge.
The 46º halo is much rarer and fainter than the 22º version: It is only seen when the ice crystals are just right. Either kind of halo is a sign of low pressure coming in, and often means there is rain and other wintry weather on its way.
To more aerial spectra...