Last night I came across this phenomenon in my native town and went on to research about it. Well, it's actually very common but a mysterious event. The image from my cam will be down at the end of the article.
The 22° halo (both lunar and solar) , is a very common event in the nature occurring about twice a week, which is more frequent than that of a rainbow.
Why does this happen?
Halo in general is a ring of light. This can be observed from the light of the sun (commonly called the solar halo) or the moon (commonly known as the lunar halo).
The 22° halo is due to the refraction of lunar light through thousands and thousands of tiny ice crystals present in the atmosphere. These ice crystals are hexagonal in shape and light enters as it gets refracted and re-emerges from it getting refracted again. This whole refraction process bends the light by about 22° and that's how it got the name. Even the ring's radius around the sun is about 22°. There is also some reflection involved in this phenomenon. The moon ring is also referred to as the winter halo as it occurs generally in the winter.
This is generally white in colour but sometimes it looks something like a rainbow because of the dispersion of light through the crystals.
How the halo got it's exact orientation?
Well the orientation of the ice crystals for giving the halo it's particular shape still remains a mystery. It is almost impossible to recreate this event in lab. The halo actually forms on the high cirrus clouds (thin clouds with wispy strands) as they are moving. It was previously thought that this could be due to the random orientation of the crystals in columns but this was disputed by the fact that they actually appear to be horizontal with respect to each other. Nowadays it is thought to be like a cluster of bullet shaped ice column.
Is it really rare?
Though it occurs quite often, it's difficult to observe. Because the ice crystals need to be oriented perfectly with your eyes. It keeps happening but most of the times we forget to look over our heads. In other words halo is exclusive to each one of you. The halo I'm seeing will be different from the one you are as the crystal refracting the lights for me will be different from that of yours. Well to cut it short the lunar halo occurs quite commonly and most of the times is not properly observable. But as of today the halo that I saw was properly oriented so that we all were able to see it at the same time.
What does it signify?
It is said in folklores that the halo brings rain or storm which actually is scientifically right. The high cirrus clouds actually bring rain. Don't mistake it with corona (not the pandemic one obviously) which is also a similar phenomenon that occurs due to refraction through the droplets of water and not crystals of ice.
Here are the images of lunar halo that I observed yesterday. From cuttack, India.
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