Scientists say that halos are clear indication of upcoming rains. They used to be bright and and colourful. It is ring of coloured light formed around the sun when lunar or solar light passes through ice crystals.
By broad definition, a halo is a group of optical phenomena, in the form of rings, arcs, pillars, or bright spots around the sun or moon, produced by the refraction or reflection of light by ice crystals suspended in the atmosphere.
These sort of rings are the result of complex reflection and re reflexion of lights.
The fact behind the sun ring is that very often in the cloud decks around a storm system, an extensive band of cirrostratus clouds lies ahead of an approaching warm front. In the majority of cases, when sun or moonlight passes through these ice clouds, a halo forms around it.