The classical ring around the moon is caused by ice crystals as discussed in the other answers.
Ring around the moon meaning.
What does a halo around the moon mean.
Since the ice crystals typically have the same shape namely a hexagonal shape the moon ring is almost always the same.
Have you ever seen a ring around the moon in the sky and wondered what causes it.
While stargazing have you ever noticed a large circular band of light surrounding the moon.
In meteorology a corona plural coronae is an optical phenomenon produced by the diffraction of sunlight or moonlight or occasionally bright starlight or planetlight by individual small water droplets and sometimes tiny ice crystals of a cloud or on a foggy glass surface.
The ring around the moon is caused by the refraction of moonlight which of course is reflected sunlight from ice crystals in the upper atmosphere.
This is a moon halo and it s caused by light passing through ice particles suspended in the high atmosphere.
However if you see a ring around bright relatively point sources of light easier on a dark background and so at night such as the moon or stree.
From a folkloric standpoint however many traditions of weather magic indicate that a ring around the moon means bad weather rain or other foul atmospheric conditions are on the way.
In its full form a corona consists of several concentric pastel colored rings around the celestial object and a.
What is a lunar halo.
You totally might be able to tell if rain is coming if you see a ring around the moon.
If so you have seen a lunar halo.
These are called halos they are formed by light bending or refracting as it passes through ice crystals from high level cirrus clouds.
Of course the emphasis is on might and not totally and what we re seeing isn t really a function of the moon telling us what the weather will be but a more mundane atmospheric condition that just happens to be caught in the glowing light of the moon.
A lunar halo is caused by the refraction reflection and dispersion of light through ice particles suspended within thin wispy high altitude cirrus or cirrostratus clouds.